Author Topic: Helical-cut timing gears  (Read 9982 times)

Offline Late to the party

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Helical-cut timing gears
« on: July 16, 2014, 11:18:10 AM »
Will somebody please explain to me why otherwise respectable people are making these things from aluminum alloy?

Talk about planned obsolescence.

Lateness.

Offline rocker59

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Re: Helical-cut timing gears
« Reply #1 on: July 16, 2014, 11:34:46 AM »
Too quiet.

I want my gears straight-cut.

 ~;
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Offline Late to the party

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Re: Helical-cut timing gears
« Reply #2 on: July 16, 2014, 11:35:34 AM »
Too quiet.

I want my gears straight-cut.

 ~;

Saves lives, y'know.

Offline twhitaker

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Re: Helical-cut timing gears
« Reply #3 on: July 16, 2014, 11:53:10 AM »
Since aluminum (aluminium, ergal) is one third the weight of an equivalent amount of steel its inertia would be much lower. If you want a heavy flywheel, ergal gears would be a waste of money.
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Re: Helical-cut timing gears
« Reply #3 on: July 16, 2014, 11:53:10 AM »

Offline Late to the party

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Re: Helical-cut timing gears
« Reply #4 on: July 16, 2014, 12:18:26 PM »
No dispute concerning inertia. Aluminum is light, rigid and relatively strong, certainly under compression. The problem lies in the shear strength (or lack thereof) so characteristic of aluminum alloys. Assuming the presence of some lubricating substance, the faces of hardened steel gears can slide across each other many millions of times without showing appreciable wear. However, under load, each time aluminum gear faces pass each other material is removed. There is simply not enough strength at the molecular level to prevent this.

Once aluminum alloy timing gears are installed, the fuse is lit. Sure, you can say that about any mechanical device. They ALL fail in the end. However, with aluminum wear surfaces, the fuse is short and the rate of material loss is constant and rapid.

I know there are experienced machinists on this forum. Turning out serviceable 3-gear steel timing gear sets for Guzzis would require a two-step CNC process (first lathe, then mill). Why can't we do this?

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Offline Antietam Classic Cycle

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Re: Helical-cut timing gears
« Reply #5 on: July 16, 2014, 12:35:57 PM »
There are steel sets made. Big $$$. The guy that bought my Centauro just put a set in it.

My Guzzi came from the factory with helical cut steel timing gears.
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Offline rocker59

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Re: Helical-cut timing gears
« Reply #6 on: July 16, 2014, 12:40:02 PM »
My guess is the aluminum gears are for those who want lightweight, and accept a shorter life expectancy as a trade-out.

There are steel gears for those who want to make the opposite choice.  Heavier weight with longer life.

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guzzimike

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Re: Helical-cut timing gears
« Reply #7 on: July 16, 2014, 06:55:16 PM »
My Agostini Straight Cut Aluminum Timing Gears are still working silently since they were installed back in 2002 (* IIRC the year ).

We used Mobil 28 Grease as initial lubrication. The Gears emitted a barely audible, "supercharger-like" tone upon initial engine Start-Up; a sound which lasted maybe two seconds; then it was gone. The sound has never returned.

We opened up the engine not too long ago and the gear faces still look almost pristine.

FWIW, this engine lives 80% - 90% of its life at or above 4800 RPM. It also has a Lightened Flywheel , done by Ed Milich.

IMHO, as based on my personal experience with this particular Retrofit; the Aluminum Straight Cut Timing Gears by Agostini work well and offer long term service life.


YMMV, and  all that ...
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Offline rodekyll

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Re: Helical-cut timing gears
« Reply #8 on: July 16, 2014, 07:07:31 PM »
~30k on my ago's now and a recent inspection shows them looking good.  I'm not making a recommendation -- just sayin'.

Offline NCAmother

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Re: Helical-cut timing gears
« Reply #9 on: July 16, 2014, 08:37:15 PM »
There good for drag racing with cars.  Some people though just put in timing gears so their 83 GMC sierra's sound like they have a blower in it.  Seriously.  I'd love to have a set of solid timing gears, but I don't race so I don't need them.  From what I've heard, a set of straight cut gears gives accurate timing, but you lose a very tiny amount of horsepower.

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Re: Helical-cut timing gears
« Reply #10 on: July 16, 2014, 08:47:52 PM »
The Norton uses age hardened aluminum connecting rods.

Offline cruzziguzzi

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Re: Helical-cut timing gears
« Reply #11 on: July 16, 2014, 09:15:21 PM »
There good for drag racing with cars.  Some people though just put in timing gears so their 83 GMC sierra's sound like they have a blower in it.  Seriously.  I'd love to have a set of solid timing gears, but I don't race so I don't need them.  From what I've heard, a set of straight cut gears gives accurate timing, but you lose a very tiny amount of horsepower.

Isn't that ironic in that the newer factory "blowers" are nearly undetectable by ear. I've know of several fellas to gear their small Ford and Chevy V-8s for just that purpose.
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Offline rodekyll

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Re: Helical-cut timing gears
« Reply #12 on: July 16, 2014, 09:19:10 PM »
I'll bet they could buy and install a ringtone with the same noise for less $$ and hassle.  Hook it to a loudspeaker and pose away!

Offline cruzziguzzi

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Re: Helical-cut timing gears
« Reply #13 on: July 16, 2014, 09:22:18 PM »
I'll bet they could buy and install a ringtone with the same noise for less $$ and hassle.  Hook it to a loudspeaker and pose away!

My nephew has an ap for that (wrong thread? ;D) that picks up interference from a running engine then loops a selected sound through the cars stereo to respond to throttle fluctuations. His little Honda can sound like a Ferrari, B-17, Top Fuel dragster... whatever.


Way cheaper than gears and no swarf!
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Offline Waterbottle

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Re: Helical-cut timing gears
« Reply #14 on: July 16, 2014, 09:40:52 PM »
Question : Do the Aluminium timing gears come with some form of surface hardening ?
I know if I cut a piece of Anodized Ally the surface is quite a bit harder the the core material . ???
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Offline Aaron D.

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Re: Helical-cut timing gears
« Reply #15 on: July 17, 2014, 06:37:17 AM »
No hardcoat, but not a pure aluminum alloy either, so not soft.

Some cars used to use fiber timing gears..

Offline Rough Edge racing

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Re: Helical-cut timing gears
« Reply #16 on: July 17, 2014, 07:22:44 AM »
  Aluminum timing gears ?  Remember all those inline 6 cylinder engines in older Chevy and GMC big trucks ? They have an aluminum helical cut cam gear and steel crank gear. The aluminum cam gears never wear out. Now it's not necessarily a fair comparison between a 3000 rpm truck engine and a 8000 rpm bike engine but aluminum gears can be fine in certain situations. Heavy duty gas truck V-8's often had cast iron gears instead of a typical V8 timing chain.The cast iron gears more more durable than a chain in heavy duty use but would wear and get quite noisy (Rocker would love it  ;D)
  However it appears high speed racing or expensive street OHC  engines generally have hardened steel gears  instead of long timing chains.
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Offline Late to the party

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Re: Helical-cut timing gears
« Reply #17 on: July 17, 2014, 10:35:59 AM »
Thanks to all for your feedback and anecdotal advice/evidence.

Definitely learned a couple of things and now have an idea of what I'm going to do.

For those so interested, I have been made privy to a private gallery of images, taken by a single individual, depicting what can and frequently does go wrong with aluminum timing gears. I'll share the URL with anyone who PMs me and requests it.

Lateness.
« Last Edit: July 18, 2014, 07:42:53 AM by Late to the party »

Offline pressureangle

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Re: Helical-cut timing gears
« Reply #18 on: January 04, 2015, 12:46:03 PM »
One critical consideration in wear, particularly in sliding wear such as gear teeth, is hardness; certain materials don't play well together. Aluminum in particular doesn't like to slide on aluminum. That's why steel/aluminum combinations work ok. All aluminum gear trains like the Ago gears probably have different alloys or hardening processes amongst the gears of the set. Just a guess.
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Offline krglorioso

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Re: Helical-cut timing gears
« Reply #19 on: January 04, 2015, 07:44:26 PM »
The Norton uses age hardened aluminum connecting rods.

Yes, and the 1974 Commandos' (I have one, too) "D" marked rods are not good for more than 25K miles in most cases, from service notes I have read.

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Offline jabberwocky

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Re: Helical-cut timing gears
« Reply #20 on: January 04, 2015, 08:05:18 PM »
I just recently got a set of square cut aluminum gears from a member here on a trade. They look very good, though not totally virgin. I am planning to put them in this winter, but you all have me worrying. I don't have them in front of me at the moment, but I don't recall seeing any makers marks on them. Does anyone here have a story of them failing in their bike, or are the horror stories just speculative? Yes, it does seem like they'd be somewhat short lived compared to steel, but will they just get noisy, or will they strip and jump time?

Offline Aaron D.

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Re: Helical-cut timing gears
« Reply #21 on: January 05, 2015, 06:45:47 AM »
Just make sure they have lash, they should slip on easily.

Offline mtiberio

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Re: Helical-cut timing gears
« Reply #22 on: January 05, 2015, 07:23:02 AM »
From what I've heard, a set of straight cut gears gives accurate timing, but you lose a very tiny amount of horsepower.

straight cut gears have less HP loss than helical.

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Re: Helical-cut timing gears
« Reply #23 on: January 05, 2015, 10:07:05 AM »
straight cut gears have less HP loss than helical.

Clear ! But does anyone here know,- or have an idea about HP loss on chain drive vs. helical gears ?

Not knowing myself, but I remember a fellow motorcyclist once laughed at me (hard to forget that :D) when I expressed the idea that gears (and those were even straight cut ones) had a lesser HP loss than chain drive.

So , according to him, chain drive is the right choice in that regard. I just find that hard to believe. Especially with the kinky chain run on the Guzzi.
Not that I ever would give up on my straight cut gears though.

     Anyone ?




Offline kevdog3019

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Re: Helical-cut timing gears
« Reply #24 on: January 05, 2015, 11:24:58 AM »
I'm all for getting that little extra, but your imagination probably accounts for more than the reality of the matter.
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Offline Aaron D.

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Re: Helical-cut timing gears
« Reply #25 on: January 05, 2015, 12:51:41 PM »
I would expect the chain to be more efficient in power transmission. The point of gears is accuracy.

Offline twhitaker

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Re: Helical-cut timing gears
« Reply #26 on: January 05, 2015, 12:58:05 PM »
The big difference between a chain drive and the gear drive is inertia and it is lower inertia that allows the motor to accelerate quicker.

I replaced the gear drive system on my beast with a chain drive since I was paranoid about the exploding gear. I still have the old set available for a reasonable offer.
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Offline Alfetta

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Re: Helical-cut timing gears
« Reply #27 on: April 12, 2021, 01:59:33 PM »
Clear ! But does anyone here know,- or have an idea about HP loss on chain drive vs. helical gears ?

Not knowing myself, but I remember a fellow motorcyclist once laughed at me (hard to forget that :D) when I expressed the idea that gears (and those were even straight cut ones) had a lesser HP loss than chain drive.

So , according to him, chain drive is the right choice in that regard. I just find that hard to believe. Especially with the kinky chain run on the Guzzi.
Not that I ever would give up on my straight cut gears though.

     Anyone ?

gears, or chains them-selves should not cause any HP gain or loss (if they are not changing the original timing). both systems have a very high efficiency factor.
However the effect of the cam drive inertia will effect the engines throttle response.
each gear (or sprocket in the case of the chain system) will have it's own inertia. the sum of this inertia will consume HP only during acceleration.
note that the chain drive system, the chain needs to be included in the summation. typically a chain drive system will have a slightly higher overall inertia.

Advantages for the chain drive system:
the manufacture does not need to hold shaft centers to super precision tolerances.
chain tensioner will compensate for center distance issues in the "slack" side of the installation.

Diss-advantages for the chain drive system:
when a chain fails, there is normally large amounts of colleterial damage. not just in valves and pistons, but chains going through cases.

Advantages for the gear drive system:
typically higher valve timing control can be maintained.
failure of gear in very unlikely to cause case damage (and should be detected long before valve / piston contact occurs )

Diss-advantages for the gear drive system:
higher case bore tolerances need to be held.
high gear lash tolerances required on spur gear vs chain sprocket (they cost more)

IMHO: chains are fine esp. if the engine is operating under 8K RPM. If you are building a 12K RPM monster, then gears ( and a lot of effort to control valve float...)
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Offline n3303j

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Re: Helical-cut timing gears
« Reply #28 on: April 12, 2021, 08:27:19 PM »




BMW /2 series ran an aluminum cam gear against a steel crank gear (helical). My /2 ran that combination for 100K  miles before I sold it. Gears were fine at sale.

Seems to me some really old Clockworks ran wooden gears against metal pinions and the metal elements wore more quickly. Wooden bearings work well on metal boat propeller shafts. Running bearing surfaces don't have to be the same hardness to provide a good service life.
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