Wildgoose Chase Moto Guzzi

General Category => General Discussion => Topic started by: Philnewbike on June 21, 2021, 06:00:31 AM

Title: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Philnewbike on June 21, 2021, 06:00:31 AM
You love a good oil thread, admit it  :copcar:  This is the mother of all oil explanations for why sticking to the manufacturer oil spec is usually the best bet. [edit: I have a 2005 Breva 1100... known as a CARC or big block]

In case you don't want to read on, this is the message: low W oils like 75W90 or even 80W90 (as replacement for 85W90) could be doing more harm than good in your gearbox... And if you never ride in sub zero temperatures or for lots of short journey then the W bit is largely immaterial anyway - see last paragraph from gearbox engineer

I've checked the temperature of my bike after stopping for about 2 mins after a long gentle ride (in the north of UK in June, sunny, ambient about 20, no wind - unusual!).
The temperatures in deg C were:

Crank ~85
Barrels ~95
Gearbox ~65
Shaft drive ~45

These make sense. When running the barrel temps were about 110 at the top. The gearbox is bolted onto the hot engine so as well as internal friction it receives heat soak and the final shaft drive is relatively insulated from the hot engine and is just getting hot from friction.

Lets look at viscosities at the operating temperature of the unit in question, in this case the engine (shaft drive and gearbox is further down the page).
Viscosity at 100°C engine operating temp:

10W60 Motul             23.5 mm²/s - Guzzi recommend 10W60
15W50 Motul             19.8 mm²/s
20W60 Millers ND      22.7 mm²/s
20W50 Millers           17.6 mm²/s
10W40 Miller             15.5 mm²/s
5W40 Motul              14.1 mm²/s
30 monograde Gulf    11.2 mm²/s
50 monograde Gulf    18.2 mm²/s


The 50 and 60 viscosities are within ~10% of one another at the operating temperature so are probably ok depending on whether you ride around Lake Como in summer or the Lake District in Spring. I listed monograde as this was probably avaialable when the V7 big block was designed. Interestingly (to me  :drool:) the viscosity of 10W60 engine oil is not far off 90 weight gear oil until you go over 80 deg C, then it's significantly thicker (I plotted it). One more thing: when the original big block (i.e. the 1960s V7) was designed it would run rich (like all engines then) and therefore not quite as hot as engines now.

So lets look at the shaft drive and gearbox, for a 80W90 spec'd oil operating at about 45 degrees C in the shaft you need to know what the viscosity is at that temperature. Fortunately most oil manufacturerswill tell you the viscosity at two points: 40 and 100 C. I'll just assume 40 operating temp instead of 45 as it's easier:

Viscosity at 40 C shaft drive operating temp:
Agip 80W90         144 mm²/s - This is what Guzzi want you to use
Redline 75W90     100 mm²/s - THIS IS THIN
Miller ND 75W90    113  mm²/s
Agip 85W90      200 mm²/s  (Guzzi gearbox recommended... bit thick at 40 C)
Redline 75w140    175 mm²/s - looks fairly close to spec but you're paying for the protection of a a wide W oil and not actually using it! [/b]

Note that when a gearbox designer chooses an oil they do this based on what viscosity (and additives, e.g hypoid for shaft drive) are required at the expected operating temperature. I stress this because virtually every oil thread goes along the lines of "the manual says 90 weight so I use 75W90 super-duper $$$ oil because then get all the benefits of 90 and none of the disadvantages when cold". This is reasonable logic if you know nothing about gearbox design or oil but patently incorrect logic if you do as it will give you oil half as viscous at the actual operating temperature[/i]. The correct logic should be along the lines of: "at the expected operating temperature, my alternative oil has a similar viscosity, but is thinner when cold which helps for the first couple of miles". For the shaft that seems to be something like a 75W140. But note you're paying top dollar for a spec that is never used.

For the gearbox, which is what people are usually wanting to improve in terms of noise or feel, the story is slightly more tricky because if the expected operating temperature is ~65 deg C then we have to plot a line between the two temps the oil supplier gives us, i.e. from 40 to 100 C. I have done this because I am an obsessive compulsive!

Viscosity at 65 C gearbox operating temp:
Agip 85W90           74 mm²/s   - This is what Guzzi want you to use
Redline 75W90       47 mm²/s   - THIS IS THIN
Redline 75w140      81 mm²/s   - This seems similar but is expensive
Fuchs bus 90          70 mm²/s   - This seems similar but is dirt cheap
Fuchs BOA LS 90     82 mm²/s    - Similar, cheap and good quality
Eni Agip 80W90       54 mm²/s   - This is what Guzzi recommend for the shaft so if you put it in the gearbox as well it is too thin - is also recommended by several online oil selector tools


So, clear as mud now yeah ??  :thumb:


I'll leave you with this excellent snippet of information from this thread that lists an interview with Getrag (BMW gearbox builder) engineers, Klaus Sommer and Eberhard Schaetzle. SLightly different specs for BMW but I hope you can see the argument is similar, i.e. gearbox designers know what they're doing!  https://www.ukgser.com/forums/showthread.php/346792-R1100gs-clunky-gearbox

SCHAETZLE: Oil should be seen as an integral part of the transmission. When designing the transmission the load bearing capability of the oil is part of the calculation. We fill the BMW transmissions with SAE 90 GL 5 gear oil manufactured by Fuchs, a brand mainly found as an OEM supplier.
SOMMER: SAE 90-Oil should be used throughout the whole year. It istrue that in winter the shifting will suffer at first from the thick oil, but it should improve during a very short ride. For those to whom this is disturbing, because they make many short trips, for example, can use 75w90 GL 5 in winter as an alternative. In summer it must be changed back to SAE 90 GL 5.
Title: Re: Oil explanation for Guzzi (&BMW) owners confused about gear 75/80/90 weight
Post by: Kev m on June 21, 2021, 07:40:21 AM
Great data - though you should probably note the bike you were using for standards and testing as the smallblocks and CARCs differ in certain recommendations and, I'm assuming may therefore differ on internal operating conditions.

Of course, I think smallblock recs vary too by model/year.

EDIT - ok, I pulled up some data that might help clarify.

CARC, 2TB smallblock Breva 750/Nevada,V7C/R, 1TB Smallblock (I, II, and III), V9, V85, Cali 1100 (hydro and flat tappet) and Cali 1400:

Engine Oil: all spec 10/60  (except hydro Cali 1100 which was 5/40, and flat tappet Cali 1100 could also use 20-50)

Transmission Oil (Gearbox in MG speak):

* 80/90 - 2TB smallblock (Breva/Nevada, and presumably V7C/R), and Cali 1100

* 85/90 (GL-5) -  CARC (B11 shop manual and 2006 Tech bulletin), V7 Mk I, and Cali 1400

* 75/90 (GL-5) - V7 III (and presumably II, I don't have a manual), V9

* 75/140 (GL-5) - V85

* 85/140 - CARC (B11 owner's manual) - presumably this is wrong, superseded by 2006 Tech Bulletin


Final Drive Oil (Transmission in MG speak):

* 80/90 (GL-4) - CARC (B11 workshop manual), Cali 1100 and Cali 1400

* 85/140  (GL-4 or GL-5) - CARC (B11 owner's manual but presumably wrong per tech bulletin), 2TB smallblock (Breva 750/Nevada/V7C/R [presumably]), 1TB smallblock (V7 I, II [presumably], and III, V9)

* 75/140 (GL-5) - V85



NOTE: I'm personally too removed from the CARCs now. I haven't had one in more than half a decade and I only have old tech data on the B11 so maybe someone could check/correct what I've posted here for that. I also found a discrepancy in the little information I actually have (Workshop vs Owner's manual contradict each other). Hell both of those publications are old enough that they actually have the engine oil a 5-40 and not the 10-60 to which the tech bulletin later updated the recommendation.

EDIT to EDIT - OK, I added the tech bulletin stuff too.
Title: Re: Oil explanation for Guzzi (&BMW) owners confused about gear 75/80/90 weight
Post by: Philnewbike on June 21, 2021, 08:51:50 AM
Hi Kev. Thanks for the extra info, very interesting (to a madman like me), I have added my model now. Also, see my guesses at what the differences below mean. Cheers

Great data - though you should probably note the bike you were using for standards and testing as the smallblocks and CARCs differ in certain recommendations and, I'm assuming may therefore differ on internal operating conditions.

Of course, I think smallblock recs vary too by model/year.

EDIT - ok, I pulled up some data that might help clarify.

CARC, 2TB smallblock Breva 750/Nevada,V7C/R, 1TB Smallblock (I, II, and III), V9, V85, Cali 1100 (hydro and flat tappet) and Cali 1400:

Engine Oil: all spec 10/60  (except hydro Cali 1100 which was 5/40, and flat tappet Cali 1100 could also use 20-50) 10/60 is the same as my carc but guess they realised the hydraulic tappets only work well with thinner 5/40 oil at least in first few minutes. So they decided to sacrifice some protection for a quiet bike that customers don't take back to the workshop claiming it's noisy!

Transmission Oil (Gearbox in MG speak):

* 80/90 - 2TB smallblock (Breva/Nevada, and presumably V7C/R), and Cali 1100 I can see small blocks not needing quite as heavy oil but not sure why Cali 1100 wouldn't unless they're logic is it's not driven as hard, ie on freeway at 55mph lol...?

* 85/90 (GL-5) -  CARC (B11 shop manual and 2006 Tech bulletin), V7 Mk I, and Cali 1400 I guess for v7 mk1 they just played safe before deciding on 80W90 later??

* 75/90 (GL-5) - V7 III (and presumably II, I don't have a manual), V9  I think lower power, higher internal gear speed => thinner oil is ok

* 75/140 (GL-5) - V85   I would say that this style of bike might be doing anything from pottering to the shops to very high load / high temp off roading. To cover all possibilities without need to suggest multiple specs they just filled it with a modern very wide multigrade for simplicity (it's not as expensive as it once was either)

* 85/140 - CARC (B11 owner's manual) - presumably this is wrong, superseded by 2006 Tech Bulletin  Yep that seems to be the case


Final Drive Oil (Transmission in MG speak):

* 80/90 (GL-4) - CARC (B11 workshop manual), Cali 1100 and Cali 1400

* 85/140  (GL-4 or GL-5) - CARC (B11 owner's manual but presumably wrong per tech bulletin), 2TB smallblock (Breva 750/Nevada/V7C/R [presumably]), 1TB smallblock (V7 I, II [presumably], and III, V9)   This one's more of a puzzle: yes breva spec is wrong, but why would a small block need heavier oil here... are the gears a larger pitch (coarser) perhaps? Whatever it is I would assume they're running a bit hotter than the CARC bikes do.

* 75/140 (GL-5) - V85  See v85 point above: grade for very wide range of expected uses



NOTE: I'm personally too removed from the CARCs now. I haven't had one in more than half a decade and I only have old tech data on the B11 so maybe someone could check/correct what I've posted here for that. I also found a discrepancy in the little information I actually have (Workshop vs Owner's manual contradict each other). Hell both of those publications are old enough that they actually have the engine oil a 5-40 and not the 10-60 to which the tech bulletin later updated the recommendation.

EDIT to EDIT - OK, I added the tech bulletin stuff too.
Title: Re: Oil explanation for Guzzi (&BMW) owners confused about gear 75/80/90 weight
Post by: Kev m on June 21, 2021, 09:08:57 AM
Hi Kev. Thanks for the extra info, very interesting (to a madman like me), I have added my model now. Also, see my guesses at what the differences below mean. Cheers


I'm guessing you're a bit like me and you enjoy getting lost in the minutia.  :thumb:

Some thoughts on your SWAGs below. My new ones in red.


Engine Oil: all spec 10/60  (except hydro Cali 1100 which was 5/40, and flat tappet Cali 1100 could also use 20-50) 10/60 is the same as my carc but guess they realised the hydraulic tappets only work well with thinner 5/40 oil at least in first few minutes. So they decided to sacrifice some protection for a quiet bike that customers don't take back to the workshop claiming it's noisy!

If you're not familiar with the hydro debacle they had multiple recalls as the camshafts and lifters failed. I can't begin to guess at their logic, I just know the last recall seemed to do the trick, but by then the concept had such a black eye they gave up and went back to flat tappets (and eventually experience new failures with them a decade later on the 8Vs before going to roller rockers).



Transmission Oil (Gearbox in MG speak):

* 80/90 - 2TB smallblock (Breva/Nevada, and presumably V7C/R), and Cali 1100 I can see small blocks not needing quite as heavy oil but not sure why Cali 1100 wouldn't unless they're logic is it's not driven as hard, ie on freeway at 55mph lol...?

* 85/90 (GL-5) -  CARC (B11 shop manual and 2006 Tech bulletin), V7 Mk I, and Cali 1400 I guess for v7 mk1 they just played safe before deciding on 80W90 later??

* 75/90 (GL-5) - V7 III (and presumably II, I don't have a manual), V9  I think lower power, higher internal gear speed => thinner oil is ok

Actually with the smallblocks the progression is 80/90 on the older 5-speeds, 85/90 for the Mk I V7, and then the MK II and III changed to 6-speeds (and that's how the V9 debuted) with half the capacity and an oil pump and went with 75/90. But keep in mind that all the hemi-head smallblocks make more power than the previous generations of smallbocks.
 

Final Drive Oil (Transmission in MG speak):

* 80/90 (GL-4) - CARC (B11 workshop manual), Cali 1100 and Cali 1400

* 85/140  (GL-4 or GL-5) - CARC (B11 owner's manual but presumably wrong per tech bulletin), 2TB smallblock (Breva 750/Nevada/V7C/R [presumably]), 1TB smallblock (V7 I, II [presumably], and III, V9)   This one's more of a puzzle: yes breva spec is wrong, but why would a small block need heavier oil here... are the gears a larger pitch (coarser) perhaps? Whatever it is I would assume they're running a bit hotter than the CARC bikes do.

Yeah that's my sway - the rear drive on the smallblocks is that much smaller overall, but aside from lower hp output there are likely similar forces overall. I'm just guessing it's a harsher environment overall than on the larger/beefier CARCs.

 


Title: Re: Oil explanation for Guzzi (&BMW) owners confused about gear 75/80/90 weight
Post by: Philnewbike on June 21, 2021, 09:15:25 AM
Hi Kev
Good discussion. I would guess that the addition of a oil pump meant that 75W was now a necessity on a (potentially) zero degree day when 80W or 85W might be too thick to pump affectively whereas an old model will simply drag oil up due to the dipped gear system of lubrication. Not sure about change from 80W90 to 85W90 unless that was just another a typo!
cheers
phil
Title: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: John Warner on June 21, 2021, 10:02:21 AM
My CARC Oil (2009 Stelvio) has never got any hotter than around 40°C/104°F (I have a Temp Sensor in the Fill/Level Plug).
That was in ambient temps of around 24°C/75°F, and riding fairly 'briskly'.
I'll move the Sensor to the Gearbox at some point soon, just out of curiosity.
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Kev m on June 21, 2021, 10:09:45 AM
My CARC Oil (2009 Stelvio) has never got any hotter than around 40°C/104°F (I have a Temp Sensor in the Fill/Level Plug).
That was in ambient temps of around 24°C/75°F, and riding fairly 'briskly'.
I'll move the Sensor to the Gearbox at some point soon, just out of curiosity.

How accurate is the sensor in your estimation.

And how much does that reflect the peak internal temperature that the oil can reach in the passageways of say the head or when squirted on the pistons?

I ask because I used to take infra-red head temps on a number of my Guzzis and Harleys. IIRC (and it's been a while) I would regularly see head temps in the high 200's (F) on my B11. I would think that oil in the exhaust valve cooling passage and hitting the piston would be getting hotter, even if that heat is shed by the time it gets back to the sump.

I've not had any sump temperature gauges on my Guzzis, but I've had them on a number of Harley Sportsters and peak head temps hitting mid 200's (F) might show up as remote oil sump temps in the 160-180F range while head temps in the low 300's might show as high as 210-230 (F) in the remote sump.
Title: Re: Oil explanation for Guzzi (&BMW) owners confused about gear 75/80/90 weight
Post by: Wayne Orwig on June 21, 2021, 10:22:18 AM
Engine Oil: all spec 10/60  (except hydro Cali 1100 which was 5/40, and flat tappet Cali 1100 could also use 20-50) 10/60 is the same as my carc but guess they realised the hydraulic tappets only work well with thinner 5/40 oil at least in first few minutes. So they decided to sacrifice some protection for a quiet bike that customers don't take back to the workshop claiming it's noisy!

If you're not familiar with the hydro debacle they had multiple recalls as the camshafts and lifters failed. I can't begin to guess at their logic, I just know the last recall seemed to do the trick, but by then the concept had such a black eye they gave up and went back to flat tappets (and eventually experience new failures with them a decade later on the 8Vs before going to roller rockers).



I always like a good oil thread...... (not)
Just to toss in my $0.02 on the hydro thing. My take on the attempts to fix it where that some engineer thought that if a hydro lifter leaked down, the initial pounding as it pumped up, was the entire problem. Thus the 5w40 to get them to pump up fast when cold, and even an attempt at shimming the lifters, to reduce the amount of hammering on cold start. But even after they discovered that it was a valve spring issue, they stayed with the 5w40. I still use 5w40, but have a feeling that a 10w40 is probably a bit better for that motor. I have no proof, and I am dumb, so I stick with the 5w40.

Flame away, just thinking out loud.
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Philnewbike on June 21, 2021, 11:01:52 AM
I really like your scientific bent chaps. Be curious to see what real oil temps you find Wayne, as opposed to my IR temps... assume similar if final drive was similar. As Kev rightly says there is still the point that oil actually gets much much hotter in the engine as it's used to some extent as a coolant. But the main point I wanted to make came about because several online oil retailers and big oil companies 'oil selectors' said 75W90 (or 80W90) for the gearbox and final drive and that is simply wrong. If anything, for most riders, straight 90 weight would be best for gearbox.
Cheers
phil
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Old Jock on June 21, 2021, 02:16:53 PM
Shockproof heavy is popular with a lot of owners and many have used it in the box for many thousands of miles without issue.

From your data the Shockproof Heavy seems to be pretty close to what Guzzi quote viscosity wise at your running temperature, for the CARCs

I'm running it at the moment, in an older 5 speed box which quotes 80W-90 but as long as the oil is changed regularly and there's enough of it, I'm fine

I agree a wide multigrade is a bit pointless as the gear and bevel box don't run very hot in comparison to ambient, in the UK its definately not an issue.

As far as the engine is concerned, the older bikes quote a 20/50 I'm running a 15/50 full synth in an LM 1000, Sport 1100 and a HiCam engine. The difference in oil temp and pressures in these bikes is markedly different. The HiCam is the problem child and runs in clear air 20C ambient, around 110C, sump temp and overheats in traffic PDQ, pressure also starts to drop through the floor. When I say overheat sump temps 120-130C. I'm upping to a 10/60, as many who run HiCams do and overfill the sump by around 10-15 mm above the max level, but that's another story. IMHO factory specs are to be used where no data exists to prove otherwise, but shouldn't be regarded as set in stone, if you've got data that suggests a possibly better alternate

The QC at least on my old bikes were variable to say the least, and one bike out the factory might run hot another cold, or one may have good oil pressure another not.

Unless you gather the data to know what you're pressures and temperatures are, you're could be whistling in the wind, at least for the older models (up to early into the 2000s)

Guzzi used straight cut gears in some 5 speeders then went to helical. I'm no tribologist but I would have thought that these might require different oils, not according to Guzzi anyway. Perhaps I'm unduly hard on Guzzi but I do sometimes wonder how much engineering really went on at certain times.

Thanks for the information though it's nice to see somebody take a step by step logical approach to the issue and narrow down alternatives in a logical manner, appreciate the data  :bow:
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Two Checks on June 21, 2021, 04:50:19 PM
What ever happened to good old yak fat?
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: berniebee on June 21, 2021, 05:23:42 PM
I've got a point to make, so bear with me while I go over some things. Oil varies in viscosity with temperature- the hotter the oil, the lower the viscosity. But it's important to note that this change is not linear with temperature.
The red curve below shows viscosity vs temperature for 10W60 engine oil, and gear oil has the same hyperbolic curve.
   
(https://i.ibb.co/2F4NRTg/Graph-Oil-Cast-RS-10-W60-1024.png) (https://ibb.co/2F4NRTg)


The second point I want to make is that the operating temperature of the engine, transmission and rear wheel drive varies directly with the daily ambient temperature. In other words, if your engine's operating temperature is 90C today at an ambient 20C, the engine temperature will be 95C when the temperature hits 25C tomorrow . Same story for the transmission and rear wheel drive.
 
Now, let's look at the right portion of the red curve. This part of the curve looks almost flat, doesn't it? This shows that the viscosity at about 100C doesn't vary much with a change in temperature.  So for an engine at operating temperature, a change in ambient temperature is not going to affect the viscosity much. (Yes, the oil will breakdown more quickly at higher temperatures, but that's another discussion.)

But it's a different story for the left side of the graph.  Viscosity varies wildly at cooler temps. Note how the graph shows a viscosity of 450 at 20C (room temperature.),  275 at 30C, 175 at 40C, about 100 at 50C, and 75 at 60C! These are all "operating temperatures " of the rear wheel drive, depending on the climate and season you are riding in. Even with the owners using the same brand of oil, the rear wheel drive of a Florida Guzzi consistently sees an oil that has a fraction of the viscosity of a rear wheel drive in rainy, cool England.
 
Conclusion: For the rear wheel drive, oil type is not that critical folks. These rear drives are designed to tolerate a huge variation in oil viscosity. Add moly* and you can use any of the oils mentioned in the OP's list.

* Or ensure your choice of oil has moly.


Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: moto-uno on June 21, 2021, 06:49:29 PM
  The only part that's unfortunate here is that other than Motul ( short for bring cash ) is none of the other oils listed are
available here in B.C ( and probably the rest of Canada ). It'd be nice to see Pennzoil , Amsoil , Quakerstate or Castrol
checked for a future in depth check :) . Thanks for the read , Peter


Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: jcctx on June 21, 2021, 07:13:23 PM
Gear oil good~ use some!!!
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: ozarquebus on June 21, 2021, 09:29:34 PM
What I do not understand is how Redline MT-90 fully synthetic gear oil can be substituted for motor oil, but I read that somewhere...
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Philnewbike on June 22, 2021, 03:36:51 AM

As far as the engine is concerned, the older bikes quote a 20/50 I'm running a 15/50 full synth in an LM 1000, Sport 1100 and a HiCam engine. The difference in oil temp and pressures in these bikes is markedly different. The HiCam is the problem child and runs in clear air 20C ambient, around 110C, sump temp and overheats in traffic PDQ, pressure also starts to drop through the floor. When I say overheat sump temps 120-130C. I'm upping to a 10/60, as many who run HiCams do and overfill the sump by around 10-15 mm above the max level, but that's another story. IMHO factory specs are to be used where no data exists to prove otherwise, but shouldn't be regarded as set in stone, if you've got data that suggests a possibly better alternate

Thanks for the information though it's nice to see somebody take a step by step logical approach to the issue and narrow down alternatives in a logical manner, appreciate the data  :bow:

Thanks for that.
BTW you might want to consider an oil designed to run hot ?  https://www.opieoils.co.uk/p-1006-red-line-high-performance-synthetic-motor-oil-20w-50.aspx  (no data sheet though so no idea on viscosity)
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Stretch on June 22, 2021, 05:13:44 AM
Interesting thread with input from some very knowledgeable people.

But we're pretty deep into the weeds here! :grin:

I can remember reading some spirited discussions about how the oil
in UJMs was SO inadequate for the transmissions, and how they'd
wear out in no time, yet there are plenty of unit construction bikes
tooling around quite happily with 100K-plus on the clock.

Use your favorite flavor of hypoid gear oil, and enjoy the ride. The
mechanicals will probably outlast you.

I'd bet you could get a surprising amount of miles out of a rear end
lubed with ATF. Some body ought to try that.......
 
                                                            -Stretch
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Philnewbike on June 22, 2021, 08:11:44 AM
Hiya. My replies below in purple in good faith (Oh no: oil thread descends into typical oil thread thread... play nicely children lol.)

I've got a point to make, so bear with me while I go over some things. Oil varies in viscosity with temperature- the hotter the oil, the lower the viscosity. But it's important to note that this change is not linear with temperature.
The red curve below shows viscosity vs temperature for 10W60 engine oil, and gear oil has the same hyperbolic curve.

It isn't hyperbolic but exponential gives a reasonable fit. So what I did was plot a straight line between data points on a *log plot*, hence my interpolations are on an exponential plot- so no, they are not linear. See here for log-linear viscosity plot and how it is fairly straight (i.e. exponential) from 40 to 100 C  https://www.engineeringtoolbox.com/dynamic-viscosity-motor-oils-d_1759.html    :popcorn: 

The second point I want to make is that the operating temperature of the engine, transmission and rear wheel drive varies directly with the daily ambient temperature. In other words, if your engine's operating temperature is 90C today at an ambient 20C, the engine temperature will be 95C when the temperature hits 25C tomorrow . Same story for the transmission and rear wheel drive.

Hmmmm, I need to do a bit of thermodynamics on that 😊 I think you’re right according to convective heat formula (heat energy proportional to change in temp of object and air flow) but I think it may be more complex than that… will have a think! But yes on first though it seems my 45 deg C shaft in ambient temp of 20 may run at 65 deg C in ambient temp of 40 deg C... not 100% sure tbh
 

Now, let's look at the right portion of the red curve. This part of the curve looks almost flat, doesn't it? This shows that the viscosity at about 100C doesn't vary much with a change in temperature.  So for an engine at operating temperature, a change in ambient temperature is not going to affect the viscosity much. (Yes, the oil will breakdown more quickly at higher temperatures, but that's another discussion.)

I've plotted *real* data as an exponential function - it does change viscosity. It looks like it doesn't because you're looking at a linear-linear plot and it's hard to see. As an example, from 90 to 100 C the viscosity of high quality Motul fully synth 10W60 changes from about 30 to 20 mm/s^2 (this will be more for mineral). That's not bad or wrong or something to worry about, it's just interesting... You think 10 mm/s^2 change in viscosity is a smaller value compared to the change at the cooler end. And you're right. But as a percentage change in viscosity it is quite large, i.e. decrease of 33% from 90 to 90100 deg C. If you sit at the lights on tickover for a long time on a hot day and your engine oil gets hotter and hotter with no air flow to take the heat away and the oil light comes on: that's why, lower and lower viscosity


But it's a different story for the left side of the graph.  Viscosity varies wildly at cooler temps. Note how the graph shows a viscosity of 450 at 20C (room temperature.),  275 at 30C, 175 at 40C, about 100 at 50C, and 75 at 60C! These are all "operating temperatures " of the rear wheel drive, depending on the climate and season you are riding in. Even with the owners using the same brand of oil, the rear wheel drive of a Florida Guzzi consistently sees an oil that has a fraction of the viscosity of a rear wheel drive in rainy, cool England.

I beg to differ (not done full calculations though so happy to be persuaded!). I reckon the oil operating temp after say 20 miles of riding will be similar whether ambient temp of 5 deg or 40 deg C (typical extremes of riding temps). Yes hotter in Florida, cooler in England. But I bet my house a bike ridden at 40 C and one ridden at 0 C will not have 40 C difference in shaft or engine temperature as your logic has it above - that's instinctively wrong but according to simple convection theory it is right... surely is more complicated than that no? BTW, the change only *looks* larger at lower temperature. Do the maths and you'll see it is just a trick of the exponential (approx.) curve - plot it as log-linear and it's much clearer!
 
Conclusion: For the rear wheel drive, oil type is not that critical folks. These rear drives are designed to tolerate a huge variation in oil viscosity. Add moly* and you can use any of the oils mentioned in the OP's list.

Remember folks, see the passage I posted from BMW Getrag engineers in the last paragraph of my post regarding their view of replacing 90 with 75W90... if you always ride in cold climate, yes can use 75W if you want, if you usually ride in mild climate just stick to the spec. And if you thrash it is hot climate maybe go more viscous...... i think :boozing:

* Or ensure your choice of oil has moly.



 Good to have the brain cells stretched, cheers 😊
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: kballowe on June 22, 2021, 08:39:27 AM
This five gallon bucket says "multi-purpose" on the label, so it must be good stuff.
It would be a lifetime supply.

(https://live.staticflickr.com/65535/51263777016_1f5069ef61.jpg)
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: wymple on June 22, 2021, 09:18:16 AM
I've spent my entire riding life with drive boxes filled with any weight I found on sale. Because I'm an old fart, I was always a fan of STP. It was the go to solution to keeping old worn out junk on the road back in the day. To this day I still put an ounce or two in my final drives. I have never lost a gearbox nor come close. I doubt I'm about to start worrying now.
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Philnewbike on June 22, 2021, 09:31:06 AM
Yep maybe true, unless you're racing in Riyadh.
I think for gearbox protection and change quality it's probably important though.
Cheers
p
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: SmithSwede on June 22, 2021, 03:25:40 PM
Interesting thread.   And yes, I follow the Owner’s Manual and run the recommended 85-90 oil in the gear box of my V7 smallblock (which is a lot harder to find than 80-90).

Here’s my concern with this analysis.  The starting premise is that Guzzi makes recommendations in the manual which are the conclusions of deep technical analysis and thus the Baseline Platonic Truth.  What possible reason do we have to believe this is some profound truth, given we know that the spec can vary over time, that Guzzi has botched the spec with the hydro debacle, and given that oil companies pay off manufacturers to recommend their products?

What evidence do we have that if you ride normally and change the oil somewhat regularly, that these viscosity variations make a practical difference?

For most people, there is no practical difference between a gearbox that can last “only” 150,000 miles on the “wrong” oil but 300,000 miles on the “right” oil.   Why?  Because they junk the bike well before 20,000 miles. 

I suspect the biggest factor for longevity is probably regular oil changes to remove water contamination and metal shards.  And I bet it matters a lot that some people shift smoothly and accelerate smoothly and thus keep their gears happy, whereas other bang on the box and otherwise torture it. 

I’d certainly be interested in data from, say, a bike rental fleet that showed a real world difference just based on gear oil viscosity differences. 

Maybe the old moly recommendation is part of that data?  But my understanding is that the GL5 spec obviated the need for moly.   What would happen to gears that didn’t get the moly treatment?  And did any of that have anything to do with viscosity?
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Stretch on June 22, 2021, 04:28:24 PM
Quote
What evidence do we have that if you ride normally and change the oil somewhat regularly, that these viscosity variations make a practical difference?

Exactly!

During WWII, they did all kinds of analysis on engines, metallurgy, etc..  Before the common use of oil filters,
they found that a magnetic drain plug made a HUGE difference to the longevity of internal engine components.

Change your oil and filter on a regular basis, your air filter on a regular basis, (or use a K&N - another K&N thread
coming on!  :shocked: ), use magnetic drain plugs, and use whatever oil floats your boat that's close to original spec or better.

Then, RIDE AND HAVE FUN!   :-)

                                                         -Stretch :grin: :cool: :thumb:
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Tom H on June 22, 2021, 04:56:54 PM
Since were are on gear oil.

GL4 or 5. Did I read right that a rear drive is specifying GL4? I thought that went away with the Loop 4 speed gearbox?

EP (Extreme Pressure) additives? I was reading the manual for my '62 F100 about what oil to use in the gearbox, rear drive and steering box. I had read/heard somewhere that it was 20wt motor oil in the gearbox. I wanted to make sure what it needed. It said to use 90wt gear oil NO EP ADDITIVES or 50wt motor oil in the gearbox and I think rear drive as well. I looked at my jugs of 85/90 GL4 and GL5. GL4 has the EP, the GL5 did not say it on the label. Maybe GL5 has EP additives built into the formula, not an additive?

Why would Ford specify NO EP in a 4 speed granny 1st gearbox??

Tom
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: RinkRat II on June 22, 2021, 05:51:03 PM

     EP additives and Brass synchros don't play well with each other.

       Paul B :boozing:
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Philnewbike on June 23, 2021, 11:17:38 AM
Interesting thread.   And yes, I follow the Owner’s Manual and run the recommended 85-90 oil in the gear box of my V7 smallblock (which is a lot harder to find than 80-90).

Here’s my concern with this analysis.  The starting premise is that Guzzi makes recommendations in the manual which are the conclusions of deep technical analysis and thus the Baseline Platonic Truth.  What possible reason do we have to believe this is some profound truth, given we know that the spec can vary over time, that Guzzi has botched the spec with the hydro debacle, and given that oil companies pay off manufacturers to recommend their products?

What evidence do we have that if you ride normally and change the oil somewhat regularly, that these viscosity variations make a practical difference?

For most people, there is no practical difference between a gearbox that can last “only” 150,000 miles on the “wrong” oil but 300,000 miles on the “right” oil.   Why?  Because they junk the bike well before 20,000 miles. 

I suspect the biggest factor for longevity is probably regular oil changes to remove water contamination and metal shards.  And I bet it matters a lot that some people shift smoothly and accelerate smoothly and thus keep their gears happy, whereas other bang on the box and otherwise torture it. 

I’d certainly be interested in data from, say, a bike rental fleet that showed a real world difference just based on gear oil viscosity differences. 

Maybe the old moly recommendation is part of that data?  But my understanding is that the GL5 spec obviated the need for moly.   What would happen to gears that didn’t get the moly treatment?  And did any of that have anything to do with viscosity?

Yes I agree regarding MG. Basically I just do this for kicks as I'm interested in the science. Although I am an engineer I am not a gearbox designer or oil tribologist but I do work with some people who are. They use alll sorts of (largely empirical) charts to spec oils for gearboxes... there's plenty of research been done. As an example I was told that a too thick oil can actually give a smaller film protection because the high viscosity heats up the oil (in the contact point) and it momentarily becomes very hot and thinner than a lower viscosity oil would for that application... so 140 weight may not necessarily be better (I don't know, it would need a proper experiment to prove in this application... maybe it is).
I suppose the reason I've started this thread with it's pseudo scientific bent is because so many oil threads are along the lines of "I've always used gravy granules in my shaft drive and my bikes have never let me down, QED", or "I've always used 75W90 and my bike's never gone wrong, QED", or some such highly subjective opinion based usually (not always) on doing a few 1000 miles on a bike before it is passed onto the new owner. I just wanted to inject some engineering. But I am no expert but from what I've been told and read about I would suggest the process MG went through is simply asking Agip what they thought would be best based on: speed, load, expected normal ambient temperature range, gear teeth pitch, clearance and finish [edit: and cost].
I think the past paragraph of my original post from the Getrag engineers sums things up best when they explain why 75W90 is not an acceptable alternative for 90 weight in their box*
* most 85W90 oils are also classified as 90 weights

Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Philnewbike on June 23, 2021, 11:21:48 AM
Since were are on gear oil.

GL4 or 5. Did I read right that a rear drive is specifying GL4? I thought that went away with the Loop 4 speed gearbox?

EP (Extreme Pressure) additives? I was reading the manual for my '62 F100 about what oil to use in the gearbox, rear drive and steering box. I had read/heard somewhere that it was 20wt motor oil in the gearbox. I wanted to make sure what it needed. It said to use 90wt gear oil NO EP ADDITIVES or 50wt motor oil in the gearbox and I think rear drive as well. I looked at my jugs of 85/90 GL4 and GL5. GL4 has the EP, the GL5 did not say it on the label. Maybe GL5 has EP additives built into the formula, not an additive?

Why would Ford specify NO EP in a 4 speed granny 1st gearbox??

Tom


Some additives will attack yellow metals used n old boxes. Also, low friction modifiers will kill synchromesh gears because they rely on friction to work properly. So for that box and good protective film + not super slippery +no additives bad for the metals used will probably be best.
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Philnewbike on June 23, 2021, 11:23:06 AM
What I do not understand is how Redline MT-90 fully synthetic gear oil can be substituted for motor oil, but I read that somewhere...

90 weight gear oil is actually a similar weight to 40/50 engine oil (different scale used) so yes, would probably work fine if you need to top up and had no 20w50... as long as that gear oil doesn't react with any yellow metals (is there in an engine??) in your engine and destroy it  :boozing:
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: moto-uno on June 23, 2021, 01:45:14 PM
  I'd like to add , if any of these "gear oils" are thought to be usable in an engine , make sure they don't have sulfur as an extreme pressure agent .
Why not , well sulfur and water can be acidic and tend to attack shell bearings . How long ? Don't know and don't care to find out :) . Peter
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Tom H on June 23, 2021, 10:28:02 PM
Thanks for the replies for my F100 gear oil. This makes sense. Loop 4 speed gear box has bushings that GL5 can hurt. IIRR specs say GL4. My F100 gear box probably has the same and synchros. BUT... the Sta Lube GL4 has EP additives per the label, maybe I shouldn't use that in a Loop 4 speed or my F100 gear box??? Maybe I need to find a NON-EP GL4 grade gear oil?

Maybe for the F100, use 50wt motor oil as a substitute like it says? Maybe even the 4 speed if the EP is bad for bushing?

Geez, this used to be simple. Grab a jug of 90wt and pour it in the gear box and rear drive of any vehicle you have. Done!

Thank you.
Tom
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Bazil on June 23, 2021, 11:14:13 PM
The manual for my 1961 Royal Enfield says to use engine oil "but on no account should heavy yellow grease be used in the gearbox".

It wouldn't have even occurred to me to use grease in a  gearbox ! Was this a thing for older low powered machines?
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: berniebee on June 24, 2021, 09:15:01 AM
Hiya. My replies below in purple in good faith (Oh no: oil thread descends into typical oil thread thread... play nicely children lol.)

 Good to have the brain cells stretched, cheers 😊

 I finally looked it up and the empirical formula for liquid viscosity is indeed a two parameter exponential. I admit some laziness here, as I saw the curve and knowing that oil will freeze into a solid given low enough temperatures (Ie: infinite viscosity) I assumed it was asymptotic - a hyperbola. The point is that it's a non linear curve. ( I will not go into arguing that an exponential decline curve is a simply a special case of a hyperbolic curve.  :grin:)

As for engine temperature being linearly dependant on ambient temperature, yes, it is somewhat more complicated than that. For example, a water cooled engine with a thermostat and switchable cooling fan will not necessarily get as hot as ambient plus a fixed number.

But for something like a rear drive (Or an air cooled engine) , I believe it's essentially correct that it's operating temperature will be ambient plus X. Here's why:
I come from an electronics background where device junction temperature is calculated as : Tj = Ta + Pd x Rja
 (Pretend the lower case letters are subscripts.)
Tj is junction (ie; device) temperature
Ta is ambient temperature
Pd is power dissipated
Rja is thermal resistance

The formula tells us that the device temperature is equal to the amount of power (times a factor) PLUS the ambient temperature. In other words,  with everything else being equal, the device temperature is ambient temperature plus X. My reasoning is that it matters not whether the heat is generated electrically or mechanically nor whether we are talking about a chunk of silicon vs a chunk of steel.

The rear drive is going to see huge variations in operating temperatures (And therefore viscosity)  with different climates and for that matter different riding styles. I agree that putting sewing machine oil or grease in the rear drive is a bad idea. But otherwise, put something labelled as gear oil in there and be done with it.

There is a far more important factor for rear drive longevity.  EP oils have support additives that get depleted over time. That can lead to gear pitting and worse. To extend the life of your rear drive, do regular oil changes. If you live in a hot climate or ride like (Insert favorite Moto GP racer here) , replace it more often!

BTW, some may be surprised to read that SAE 90 gear oil has the same viscosity as SAE  50 motor oil. It's all about the additives.





   






Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Old Jock on June 24, 2021, 09:45:22 AM
I will not go into arguing that an exponential decline curve is a simply a special case of a hyperbolic curve.  :grin:

I thought that too bernie, but not clever enough to go into the mathematics that have long since been erased from my aging brain

I did some Googling around the relationship and the easiest of the formulas I found was the Walter Equation, it uses base 10 not e and is really limited to Newtonian fluids, whereas most multigrades are non Newtonian, but I reckon might give a decent enough interpolation as just a rough guide

Formula is

log log(V+0.7)=b1+b2*logT

There is a paper I stumbled across that's pretty good on this, it's a pdf download so if you click on the link it will download it (it also give formulas for the constants and how to use the formula)

https://www.doria.fi/bitstream/handle/10024/177814/rautelin_wolter.pdf?sequence=2&isAllowed=y (https://www.doria.fi/bitstream/handle/10024/177814/rautelin_wolter.pdf?sequence=2&isAllowed=y)

Going to make up a program for my calculator (remember them?) so as I can estimate some viscosities for different grades as I'm going to change the grade on my HiCam so it would be nice to calculate some predictive percentages
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: berniebee on June 24, 2021, 10:51:07 AM
I thought that too bernie, but not clever enough to go into the mathematics that have long since been erased from my aging brain


 I remembered that factoid about trig hyperbolic curves being able to be expressed as exponential equations, but the reason I didn't want to go into it is.... because it's been far too long for me too!  :grin:
Sigh, all those advanced calculus, linear equations and probabilities classes and last week I had to Google something to help tutor a high schooler.  I even had to look up the relatively simple thermal equation for device junction temperature, just to make sure.  And I used that one frequently at times in my career. 

Yep, I'm getting old. Calculators?  Why, I was in the last year of class at my school that was forced to buy and learn how to use a slide rule, though by then every student in the class had a calculator. We all whined about it while the teacher sheepishly defended the outdated school policy.  From then on it was a class wide arms race to buy the newest, greatest Texas Instruments calculator ("It's programmable? Ooooh!").  Or an HP calculator, if you were of the weirdo Reverse Polish Notation persuasion.   Remember RPN? My youngest son (a computer science grad) tells me that RPN is still used in some programming languages and he says it's more efficient. I'd threaten him with expulsion from my will if he mentions RPN again, but he's already earning far more that I ever did. I still have an almost new slide rule somewhere in the bottom of my desk, because you know, if the entire world is destroyed by nuclear hellfire and overrun with zombies, but I need to calculate an efficient trajectory to Mars...

Thanks, I'll check out that formula - but I'll still buy whatever gear oil is on sale! 
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Old Jock on June 24, 2021, 12:11:58 PM
Yup RPN fanboy here (sorry) HPs were always my favourate but expensive here in the UK.

Used a sliderule in school too and then later went through various calculators at college, the ultimate being the HP41C. I've gone back to using an HP48GX that I had, I've just found there's a whole subculture out there extolling, using, collecting and modifying/repairing calculators. Google up HP41C prices, amazing!!

Suppose it's like owning that LM I that I lusted for as a boy but could never afford. I still don't have one but love the Magni based on the LM 1000 and it's pretty dammed close.

Just old men with too much money and time on their hands  :wink:

As far as the oils go, I agree with you, the HiCam is a bit of a special case and its engine oil grade I'm considering changing in a desperate attempt to keep oil pressure up as the dammed thing runs super hot

Anyway enough "Off Topic"  :copcar:

Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Don G on June 24, 2021, 01:05:51 PM
Royal Enfield gear box's had steel gears running on steel shafts, no bronze bushings at all. What Enfield did was pack the gear box's recesses with heavy yellow grease and then added oil until it was full, at least all of the ones I owned were like that.  DonG
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Philnewbike on June 25, 2021, 04:09:11 AM
I finally looked it up and the empirical formula for liquid viscosity is indeed a two parameter exponential. I admit some laziness here, as I saw the curve and knowing that oil will freeze into a solid given low enough temperatures (Ie: infinite viscosity) I assumed it was asymptotic - a hyperbola. The point is that it's a non linear curve. ( I will not go into arguing that an exponential decline curve is a simply a special case of a hyperbolic curve.  :grin:)

As for engine temperature being linearly dependant on ambient temperature, yes, it is somewhat more complicated than that. For example, a water cooled engine with a thermostat and switchable cooling fan will not necessarily get as hot as ambient plus a fixed number.

But for something like a rear drive (Or an air cooled engine) , I believe it's essentially correct that it's operating temperature will be ambient plus X. Here's why:
I come from an electronics background where device junction temperature is calculated as : Tj = Ta + Pd x Rja
 (Pretend the lower case letters are subscripts.)
Tj is junction (ie; device) temperature
Ta is ambient temperature
Pd is power dissipated
Rja is thermal resistance

The formula tells us that the device temperature is equal to the amount of power (times a factor) PLUS the ambient temperature. In other words,  with everything else being equal, the device temperature is ambient temperature plus X. My reasoning is that it matters not whether the heat is generated electrically or mechanically nor whether we are talking about a chunk of silicon vs a chunk of steel.

The rear drive is going to see huge variations in operating temperatures (And therefore viscosity)  with different climates and for that matter different riding styles. I agree that putting sewing machine oil or grease in the rear drive is a bad idea. But otherwise, put something labelled as gear oil in there and be done with it.

There is a far more important factor for rear drive longevity.  EP oils have support additives that get depleted over time. That can lead to gear pitting and worse. To extend the life of your rear drive, do regular oil changes. If you live in a hot climate or ride like (Insert favorite Moto GP racer here) , replace it more often!

BTW, some may be surprised to read that SAE 90 gear oil has the same viscosity as SAE  50 motor oil. It's all about the additives.





 


Hi. Very interesting. I agree with you. I've since had to remind myself about forced convective cooling and it is highly dependent on ambient temp. In summary any engine (air/oil/water cooled) that has a way to control it's running temperature by limiting the max cooling available via a thermostat will have an oil operating temperature relatively independent of ambient. And as you say, for one that doesn't (and for the final drive) the oil operating temperature is going to be very dependent on ambient temperature (I never ride in anything other than 15-25 degrees so might be hard for me to detect!). Would be interesting to see what the fellas with temp sensors find... So maybe final drive is one case where very cold/hot running riders may want to adjust their choice...

Gearbox (and engine) still slightly different case though:
I am under the (incorrect?) assumption that because the oil operating temperature in Guzzis is, lets say, ~80-90 deg C (?) and the heads are at ~110 C then because this is quite high a change in ambient temperature is only ever likely to be 10 to 20% ballpark, meaning the change is relatively small (i.e. 40 C shaft + 20 C change in ambient is 50% increase whereas 100 C engine + 20 C change in ambient is 20% change). And therefore because the gearbox is directly heated by the engine this too will have a steadier temp like the engine unlike the shaft drive. Hence I am going to stick to me guns and say 90 weight (as the Getrag people stated in the OP) is best for most conditions in gearbox unless you're planning to cross Antarctica or something. [edit: or possibly 75w140 looking at the graph at the end?]

Very good discussion, cheers all
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: kingoffleece on June 25, 2021, 04:39:52 AM
BEST THREAD EVER.  Well done, gents, well done indeed.
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Philnewbike on June 25, 2021, 08:36:54 AM
Thanks.

Here's the chart I plotted based on exponential curve (log-linear) from two data points (not every one is plotted). Obviously not ideal but the data sheets generally only give 40 and 100 C. Guzzi spec of 80w90 and 85w90 is dashed line

(NB I have tried this before in another thread and I think got the numbers a bit muddled. this one should be ok)

(https://i.ibb.co/31CG3qc/oils.png) (https://ibb.co/31CG3qc)

buy flip coin (https://freeonlinedice.com/)
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: berniebee on June 25, 2021, 09:44:41 AM
Yup RPN fanboy here (sorry) HPs were always my favourate but expensive here in the UK.


You do realize I can never speak to you again.  :cool:
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: berniebee on June 25, 2021, 10:10:23 AM



Gearbox (and engine) still slightly different case though:


Agreed, the gearbox and transmission are a different and more complicated case.   The info you posted at the start and the oil viscosity curves are much appreciated and obviously, a great thread starter!
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: SmithSwede on June 25, 2021, 08:59:32 PM
This is an interesting topic, even though I suspect it ultimately makes no practical difference. 

I’m assuming there is some kind of engineer’s formula that is used to spec things like gear oil grade and viscosity.   You plug in important parameters like the size of gears, type of gear, type of bearings, rotational speed, load, expected heat, etc.   Then the formula gives you a recommended range of outputs. 

Does anyone know that formula?  Tried to apply it to a Guzzi?

My hunch is the output of that standard formula probably translates to “75 to 90 weight is fine.   80 is optimal absent special circumstances.”
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: SmithSwede on June 25, 2021, 09:02:46 PM
Forgot to add.  I’m under the impression that gear oil differs from engine oil in that gear oil does not have viscosity improvers.    So a motor oil may act like a 10W when cold, but the VI makes it act like a 40 weight when hot. 

In contrast, gear oil has to fall within the viscosity specs “naturally.”   

I think that is because VI additives are easily sheared, and gear boxes are shear machines. 
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Mr Revhead on June 26, 2021, 02:54:42 AM
Shall we get into the importance of shear strength? Viscosity is only part of it!
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Old Jock on June 26, 2021, 03:42:13 AM
Forgot to add.  I’m under the impression that gear oil differs from engine oil in that gear oil does not have viscosity improvers.    So a motor oil may act like a 10W when cold, but the VI makes it act like a 40 weight when hot. 

In contrast, gear oil has to fall within the viscosity specs “naturally.”   

I think that is because VI additives are easily sheared, and gear boxes are shear machines.

That's interesting Smithswede, I always laboured under the (mis?)apprehension that it was viscosity improvers that gave you multigrades in the first place, however I've never been done any research into them in any detail as I'm still trying to get my head around engine oil.

Shall we get into the importance of shear strength? Viscosity is only part of it!


Would that topic not be better discussed in a separate thread, this one is complex enough for my dimm brain without inserting yet another variable?

I'm going to do some comparisons of the Walther (I miss-spelled it earlier) equation vs an exponential function just to see how they compare.

I'm thinking about engine oil, as it'd be interesting to be able to have a comparison (albeit rough) of oils of different grades at different temperatures. That way I might be able to get some sort of handle on the effect changing an oil grade might make on the pressure at running temps on my toasty HiCam, all other things being equal.

Another science experiment......... ................... :rolleyes:

You do realize I can never speak to you again.  :cool:

 :laugh: :laugh: :laugh:

John
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Old Jock on June 27, 2021, 03:52:33 AM
Question to Philnewbike

Did you use an expression like this to draw your graphs?

V=e^(b1+b2T)

Where
V is dynamic viscosity (mm^2/s or Cst)
T is temperature (K)
b1 & b2 are constants
e is Euler's constant (aka Napier's constant or base of natural logarithm)

Just wondering as I wrote a short program for my calculator for both the above and the Walther formula I posted earlier so as I can compare results
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: SIR REAL ED on June 27, 2021, 07:18:13 AM

It wouldn't have even occurred to me to use grease in a  gearbox ! Was this a thing for older low powered machines?

A not unheard of practice in the olden days.  I know a couple old timer types who had gearbox problems in vehicles using gear oil and solved them (so they claim) by switching to grease.

I would not recommend however switching to genuine Moto Guzzi Invisiable Bearing Grease (tm).  "Forgive me Father for I have sinned.  It been many years since my last confession....."
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: SIR REAL ED on June 27, 2021, 07:31:16 AM
This is an interesting topic, even though I suspect it ultimately makes no practical difference. 


As a mechanical engineer, and former mechanic on all sorts of old junk...... I'd be very comfortable betting the farm that you are right SmithSwede.

The two concerns that are probably much more a factor than actual gear face wear are 1.  Noise.  and 2.  Specifying a viscosity that makes the differential work properly (N/A for Guzzi's).

Until someone wants to perform two ride till gear failure, or ride 100k miles on two identical bikes with different oils and measure wear, it's all just fun campfire banter.

Also it is fun to spoil our babies with special oil treats.

Don't run it dry, don't fill it with cheap vegetable oil from Piggly Wiggly, don't use genuine Moto Guzzi Invisiable Bearing Grease (tm), and enjoy the ride.
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Philnewbike on June 27, 2021, 09:04:51 AM
This is an interesting topic, even though I suspect it ultimately makes no practical difference.  I disagree lol  :violent1:

I’m assuming there is some kind of engineer’s formula that is used to spec things like gear oil grade and viscosity.   You plug in important parameters like the size of gears, type of gear, type of bearings, rotational speed, load, expected heat, etc.   Then the formula gives you a recommended range of outputs.  Yes there are various charts used that deal with gear surface finish, clearance, load, speed, etc

Does anyone know that formula?  Tried to apply it to a Guzzi? Impossible without engineering drawings

My hunch is the output of that standard formula probably translates to “75 to 90 weight is fine.   80 is optimal absent special circumstances.”  As Margate Thatcher would say: no, no, no ! Please see my first post as to why  :thumb:
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Philnewbike on June 27, 2021, 09:06:56 AM
Forgot to add.  I’m under the impression that gear oil differs from engine oil in that gear oil does not have viscosity improvers.    So a motor oil may act like a 10W when cold, but the VI makes it act like a 40 weight when hot. 

In contrast, gear oil has to fall within the viscosity specs “naturally.”   

I think that is because VI additives are easily sheared, and gear boxes are shear machines.

Yes VI modifiers shear over time and the oil tends towards it's W weight. Wide viscosity gear oils do have VI improvers, but some others of high quality synthetic type naturally fulfil some W ratings, e.g. 85W90
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Philnewbike on June 27, 2021, 09:09:09 AM
Question to Philnewbike

Did you use an expression like this to draw your graphs?

V=e^(b1+b2T)

Where
V is dynamic viscosity (mm^2/s or Cst)
T is temperature (K)
b1 & b2 are constants
e is Euler's constant (aka Napier's constant or base of natural logarithm)

Just wondering as I wrote a short program for my calculator for both the above and the Walther formula I posted earlier so as I can compare results


No nothing that complicated. I had two data points and know that the function of viscosity they follow is fairly exponential. I therefore plotted the variable as a log base 10 so I could read off in-between readings. Your way sounds better
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Philnewbike on June 27, 2021, 09:12:15 AM
As a mechanical engineer, and former mechanic on all sorts of old junk...... I'd be very comfortable betting the farm that you are right SmithSwede.

The two concerns that are probably much more a factor than actual gear face wear are 1.  Noise.  and 2.  Specifying a viscosity that makes the differential work properly (N/A for Guzzi's).

Until someone wants to perform two ride till gear failure, or ride 100k miles on two identical bikes with different oils and measure wear, it's all just fun campfire banter.  Yes and no. It is objectively fact that using 75W90 instead of 85W90 or 90 will mean you're running on an oil much thinner than the oil engineers at Agip (and BMW/Getrag in my example) recommended. As for using 75W140 etc expensive stuff then yes, more subjective

Also it is fun to spoil our babies with special oil treats.

Don't run it dry, don't fill it with cheap vegetable oil from Piggly Wiggly, don't use genuine Moto Guzzi Invisiable Bearing Grease (tm), and enjoy the ride.
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Old Jock on June 27, 2021, 10:28:23 AM

No nothing that complicated. I had two data points and know that the function of viscosity they follow is fairly exponential. I therefore plotted the variable as a log base 10 so I could read off in-between readings. Your way sounds better

Now I'm just confused, although that doesn't take much.

Are you saying you used log10^x and not e^x to plot the viscosity, I thought earlier you stated that you used the exponential function, which I understand as "e", if I'm labouring under a misapprehension please tell me

I don't know if it's a better solution or not given Walther's equation uses log10, albeit twice.

Pretty easy to do as a little bit of high school algebra will give you 2 equations with 2 unknowns.

So
b1=lnV1-T1*(lnV2-lnV1)/(T2-T1)
b2=(lnV2-lnV1)/(T2-T1)
Where
T (K)
V (mm^2/s or CSt)

I reckon overall Walther's equation will probably be the more accurate of the 2 methods (see my earlier post), but even then it will be ballpark (at best).

I'm a bit off topic here as what I'm looking at is a method to calulate engine oil viscosity at different temps

What I'm trying to do is calculate what the change in viscosity will be for a given grade and manufacturer at a specific temp, percentage and absolute.

Using that I can determine the equivalent temp of the new calculated viscosity would be with my existing oil.

I already know what the pressures will be with my existing oil at various temps so I can determine if changing the oil weight would make any difference and what that the pressure difference might be

As an example I currently run 15/50 and I know that when the sump temp gets above 110C the pressure starts to nose dive and by 120C the pressure is around or a little below 10psi at idle (oil light on and confirmed with a gauge). So if I go to a 10/60 for example I could get an idea if at 120C the additional viscosity would be as high as my exisitng 15/50 at 110C (I'm just throwing out numbers here).

I know the 10 part is irrelevant but there's another reason that a thinner grade would help when cold, which I can also now roughly calculate

However theoretical and experimental are 2 quite different animals
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Philnewbike on June 28, 2021, 03:54:32 AM
Now I'm just confused, although that doesn't take much.

Disclaimer: I an an engineer but not an oil or gearbox expert (but I know a couple and have a read a lot), so though I do think I know more than the average oil threader (the reason I posted) I am by no means 'gospel' !

Are you saying you used log10^x and not e^x to plot the viscosity, I thought earlier you stated that you used the exponential function, which I understand as "e", if I'm labouring under a misapprehension please tell me

Yes. See here:https://www.engineeringtoolbox.com/dynamic-viscosity-motor-oils-d_1759.html
The plot of viscosity is approximately a straight line when done on a log10-linear graph. OK not perfect but not far off. So, given I have 2 data points (visc at 40 and 100 C is always given in data sheets) and the knowledge that log10-linear is approx straight, I fitted a line of best fit through those data points using a log10 function in Excel. I then read off the in-between numbers at eg 65 C (gearbox temp)


I don't know if it's a better solution or not given Walther's equation uses log10, albeit twice.

Pretty easy to do as a little bit of high school algebra will give you 2 equations with 2 unknowns.

So
b1=lnV1-T1*(lnV2-lnV1)/(T2-T1)
b2=(lnV2-lnV1)/(T2-T1)
Where
T (K)
V (mm^2/s or CSt)

I'm not familiar with the Walther's equation sorry

I reckon overall Walther's equation will probably be the more accurate of the 2 methods (see my earlier post), but even then it will be ballpark (at best).

I'm a bit off topic here as what I'm looking at is a method to calulate engine oil viscosity at different temps

What I'm trying to do is calculate what the change in viscosity will be for a given grade and manufacturer at a specific temp, percentage and absolute.

Good idea. I think the main thing missing from my estimate is the viscosity index (VI) variable - i.e. each oil will have it's own VI number and so will actually need a slightly different line of best fit. This goes back to what the chap above, Smithswede, was saying about gear oils and VI polymers. Actually some gear oils of wide range do use VI polymers (like 10W60 engine oil does) but in the gearbox are in a environment perfect for chopping up polymer chains and thinning the oil towards its 'W' base viscosity. E.g., if you use an 75W140 then this (according to my rough plotting) will be OK as the viscosity at the operating temp is approx same as 85W90. But, after a period of time the polymers might be chopped up and you slowly end up with a 75 weight. It is hard to say which gear oils have VI improvers and which don;t though...

Using that I can determine the equivalent temp of the new calculated viscosity would be with my existing oil.

I already know what the pressures will be with my existing oil at various temps so I can determine if changing the oil weight would make any difference and what that the pressure difference might be

As an example I currently run 15/50 and I know that when the sump temp gets above 110C the pressure starts to nose dive and by 120C the pressure is around or a little below 10psi at idle (oil light on and confirmed with a gauge). So if I go to a 10/60 for example I could get an idea if at 120C the additional viscosity would be as high as my exisitng 15/50 at 110C (I'm just throwing out numbers here).

I'd suggest 20W60

I know the 10 part is irrelevant but there's another reason that a thinner grade would help when cold, which I can also now roughly calculate

However theoretical and experimental are 2 quite different animals
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Philnewbike on June 28, 2021, 03:58:27 AM
Just to throw another cat amongst the pigeons: The original CARC Agip gearbox spec was for 85W90 and in the data sheet it says it's suitable for LS differentials. Now was that done on purpose or was it just an additional but unneeded spec of that particular oil they wanted to sell?

I am wondering if the engagement of dog gears in the gearbox are actually kept better engaged under load if the oil is not as slippery... I am guessing now!  You may or may not know but oil can have high film protection AND high or low slipperiness depending on it's design. (E.g. gear oil with high slipperiness is bad for synchromesh boxes because the syncro rings then don't work as designed - they need friction.)

If your gearbox has any false neutrals or jumps out of gear then maybe (??) 1) a return to spec and 2) use a gear oil that says it's suitable for LS differentials

Food for thought !
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Ncdan on June 28, 2021, 08:02:22 AM
Lots of very good technical information here in regards to gear oils. I changed the gear weight in my Stone when I first got it because I thought a had a minor seepage, to a heavier weight oil.
A question I have is has anyone actually experienced a rear end or transmission failure that the cause can actually be traced back to the oil that’s was in it at the time. The lack of oil is not a factor in the question.
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Old Jock on June 28, 2021, 10:56:06 AM
Thank you for the reply Phil please don't think I'm picking at your method I'm not, I'm just trying to pick up as much data as I can.

I was an egineer before I retired although competent on a good day was about my best effort.

If you are interested go to the 3rd post down on this page from the top where I listed Walther's Equation, but more to the point is a link to what (IMHO) is a pretty good paper on testing and gives a breakdown of the various calculations that can be used to interpolate (or extrapolate) oil viscosity at given temp

Many thanks for your efforts and your replies it's appreciated

John
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: krglorioso on June 28, 2021, 08:36:50 PM
     EP additives and Brass synchros don't play well with each other.

       Paul B :boozing:

I recently corresponded with RedLine oil and was told that their gear oils are completely safe to use in gearboxes that have brass or copper components.

Ralph
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: slowmover on June 29, 2021, 03:56:37 PM
What a heavy duty oil thread. Is this stuff ok?
(https://i.ibb.co/Phmvz6T/82-F6-D8-AC-D4-B0-4-A79-B79-A-06-E2-EA9-E15-DE.jpg) (https://ibb.co/Phmvz6T)
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: SmithSwede on June 29, 2021, 09:24:52 PM
Two other comments.   First, I find it amusing that we are supposed to take as received wisdom the comments of some engineers at Getrag.   But if you read the cited article, they are being interviewed in the context of explaining why BMW gearboxes suck today, and have always sucked.  Phrases spring up like “who is guilty for creating this miserable transmission?”  Why am I supposed to treat their recommendation of 90 weight as gospel?

Second, what are we to make of Guzzi specifying in their owner’s manual the use of 85W-140 oil in the gear box (and final drive) for the 1987 V75?  I bet that’s basically the same gear box as on any splash drive small block. 

Again, I think we are probably reading way to much into a spec in the manual.   But I could be wrong about that and am happy to learn. 


(https://i.ibb.co/g3Wq3sJ/418-CDE3-F-2-CC4-4-B4-E-9-C57-D4-E717-C0980-A.png) (https://ibb.co/g3Wq3sJ)
Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Philnewbike on July 06, 2021, 08:31:40 AM
Two other comments.   First, I find it amusing that we are supposed to take as received wisdom the comments of some engineers at Getrag  Fair do's, you go your way and I'll go with the gearbox engineers :thumb:.   But if you read the cited article, they are being interviewed in the context of explaining why BMW gearboxes suck today, and have always sucked.  Phrases spring up like “who is guilty for creating this miserable transmission?”  Why am I supposed to treat their recommendation of 90 weight as gospel? No one said gospel, but in a choice between using X because you think it'll be better and the gearbox/oil engineers saying use Y, I'd personally go with Y, but you can do as you wish :thumb:

Second, what are we to make of Guzzi specifying in their owner’s manual the use of 85W-140 oil in the gear box (and final drive) for the 1987 V75?  I bet that’s basically the same gear box as on any splash drive small block. I already explained the possible reasons for this earlier and also explained that this grade is fairly close to 90 anyway...

Again, I think we are probably reading way to much into a spec in the manual.   But I could be wrong about that and am happy to learn.  Yep, I think you're wrong lol but this is just for interest so as long as the box is wet I'm sure it's a lot better than dry  :thumb:


(https://i.ibb.co/g3Wq3sJ/418-CDE3-F-2-CC4-4-B4-E-9-C57-D4-E717-C0980-A.png) (https://ibb.co/g3Wq3sJ)

Title: Re: Oil explanation for Guzzi (&BMW) owners: 75W90 is not an alternative for 85W90!
Post by: Philnewbike on July 06, 2021, 08:34:15 AM
Thank you for the reply Phil please don't think I'm picking at your method I'm not, I'm just trying to pick up as much data as I can.

I was an egineer before I retired although competent on a good day was about my best effort.

If you are interested go to the 3rd post down on this page from the top where I listed Walther's Equation, but more to the point is a link to what (IMHO) is a pretty good paper on testing and gives a breakdown of the various calculations that can be used to interpolate (or extrapolate) oil viscosity at given temp

Many thanks for your efforts and your replies it's appreciated

John

Hi Old Jock

Not at all, your thoughts are very interesting, I just haven't got the patience to learn a new formula (not yet anyway)!

best wishes
Phil