Author Topic: Replacement Rod Bolts  (Read 526 times)

Offline arbezc

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Replacement Rod Bolts
« on: April 21, 2021, 03:21:01 PM »
Greetings,
I'm in the process of rebuilding a 1980 LeMans engine. The connecting rod bolts looked so good I contemplated reusing them, now I'm not so sure. Here's an image of the bolts:



After reading some of your posts I decided to take some measurements. This is what I have found:
ē   The bolts appear to be forgings, I don't any signs of damage as in void or cracks
ē   Center, fattest sections are within 0.0004Ē of each other & parallel
ē   The 2 narrow sections range about 0.002-.003Ē & tapered in the middle by about 0.001"
ē   Each nut looks to be deformed (a slight flare) at the face that contacts the rode, here's an image:



I'm not familiar with Guzzi rod bolts, does it look like they have been stretched? If so, are the current bolts supplied by MG Cycle a good replacement? I've tried to contact them over the last few days but get no response.
Any comments or suggestions are appreciated,
Thanks Charles

Offline lucky phil

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Re: Replacement Rod Bolts
« Reply #1 on: April 21, 2021, 03:40:32 PM »
The only way to tell if a rod bolt (or any bolt really) is re useable is a before and after stretch comparison between the SAME bolt. I keep that bolt information for the engines I build so when I pull them down again I can measure the removed bolt and compare it to its new relaxed limit. Carrillo SPS bolts are pretty much infinitely re useable but I still keep the new record.
How much are new rod bolts?

Ciao   
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Offline LesP

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Re: Replacement Rod Bolts
« Reply #2 on: April 21, 2021, 04:26:14 PM »
It was posted somewhere new bolts (that style) are being made again, the quality who knows.

Most shops stopped listing bolts as they were junk, even the shanks I measured were all over the place (bought from SD ) in dimension and even found one thread where someone in the UK linished them to fit the rod bores.





Maybe things have changed but OEM from the day is higher quality and actually fit the rods, I elected to reuse the (1993 spec) bolts with new nuts, the SD bolts went in the rubbish.




Donor 16/17/18/19/20 maybe more.

Offline lucky phil

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Re: Replacement Rod Bolts
« Reply #3 on: April 21, 2021, 05:34:17 PM »
You could always torque the aftermarket bolts and measure the stretch and then loosen and remeasure and see if they return to the original length. The amount they stretch for a given torque will also give you a rough idea of their quality.

Ciao
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Re: Replacement Rod Bolts
« Reply #3 on: April 21, 2021, 05:34:17 PM »

Offline arbezc

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Re: Replacement Rod Bolts
« Reply #4 on: April 21, 2021, 05:53:49 PM »
Phil, LesP,
I've read both your posts regarding deformation & poor quality. The old bolts do look to be good quality, I was hoping to reuse them.
I only saw the slight taper in them when I tried to use a micrometer. My measurements were very inconsistent due to the contact points being flat & the shank being curved. They made it easier to see a gap of about 1 thou when held up to a light. Measuring with the thin edge of a vernier back this up. If I buy new bolts I'll try the test that Phil suggested & post the results.
I would think, since the straight sections are machined, the reduced sections should be concentric (straight). Have you noticed any taper in the narrow sections of new rod bolts?
Thanks,
Charles

Offline moto-uno

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Re: Replacement Rod Bolts
« Reply #5 on: April 21, 2021, 10:35:47 PM »
 I know I'm not supposed to suggest this , but , I now have over 1/4 million kilometers on my Le Mans 2 , the rods have been
off twice to check the big end . Over 2/3's of that mileage has been with it kitted ( 70 Rear wheel horsepower ) and shown no
mercy . They are the original bolts and nuts on the rods . I believe they are up to the task :) . Peter

Online SIR REAL ED

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Re: Replacement Rod Bolts
« Reply #6 on: April 22, 2021, 04:56:58 AM »
I know I'm not supposed to suggest this , but , I now have over 1/4 million kilometers on my Le Mans 2 , the rods have been
off twice to check the big end . Over 2/3's of that mileage has been with it kitted ( 70 Rear wheel horsepower ) and shown no
mercy . They are the original bolts and nuts on the rods . I believe they are up to the task :) . Peter

Agree 110%!

Worrying about stock rod bolts as a weak link should probably be priority number 10,001 in terms of MG quality and reliability.

In the absence of obvious damage, use the stock rod bolts.  Attempting to measure bolt stretch without sophisticated ultrasonic equipment is very questionable.
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Offline Don G

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Re: Replacement Rod Bolts
« Reply #7 on: April 22, 2021, 04:57:00 PM »
Bolt stretch is easily measured with a micrometer. measure from the head to the end of the bolt, torque the sucker up and then measure overall length again, subtract one from the other and that is the stretch. One question though, do you have a spec. for stretch? Been doing this for years with ARP fasteners, but they give you the spec. In this case compare one to the others, they should all be about the same, if not replace the fastener and try again.  DonG

Offline lucky phil

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Re: Replacement Rod Bolts
« Reply #8 on: April 22, 2021, 05:16:37 PM »
Agree 110%!

Worrying about stock rod bolts as a weak link should probably be priority number 10,001 in terms of MG quality and reliability.

In the absence of obvious damage, use the stock rod bolts.  Attempting to measure bolt stretch without sophisticated ultrasonic equipment is very questionable.

Bolt stretch is measured with a Micrometer or if your really fancy a dedicated stretch tool which in essence a specialised mike. As pointed out you torque them to a pre determined stretch range and if they come back to the original length then they are good.

This is my Daytona engine getting done. I had to use the Mike as my dedicated tool wouldn't get in there.





Ciao
« Last Edit: April 22, 2021, 05:21:51 PM by lucky phil »
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Offline arbezc

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Re: Replacement Rod Bolts
« Reply #9 on: April 22, 2021, 10:14:47 PM »
Thanks for the feedback guys,
Moto, Sir - I agree with you, Guzzi rod bolts are likely ok to reuse, especially since the bike won't be ridden hard. I wasn't inferring that there's anything wrong with Guzzi parts, I'm more concerned about inconsistent aftermarket stuff.
There are many ways of working on motorcycles. There's always expediting the job to get back on the road but some of us also like to tinker & test ideas. The knowledge gained by taking an indirect route can be applied to other more difficult or costly projects. Also thereís something compelling about perfecting these funky engines.
Don, Phil - No, I don't have any specifications for stretch on Guzzi con rod bolts. Tonight I tried measuring their length with a calibrated micrometer. Itís not hard to do but measuring to less than .001" may be tricky. The stretch came to about .006-.007" which was more than I expected for only 34 ft lbs. Both the threads & bolt base were lubricated with light oil. Unfortunately my results were inconsistent; the bolt ends have some raised edges. Also the head appears to have a slight crown. I'll remove the high spots, measure again & publish my results tomorrow.
Charles

Offline Moparnut72

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Re: Replacement Rod Bolts
« Reply #10 on: April 23, 2021, 11:20:44 AM »
Some aircraft bolts have a dimple on each end. Place a ball bearing in each dimple and then measure. Ensures and accurace repeatable measurement. Pinch bolts on radial cranks have this feature.
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Offline arbezc

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Re: Replacement Rod Bolts
« Reply #11 on: April 23, 2021, 11:41:20 AM »
Greetings,
To improve measuring accuracy I put a slight dome on the bolt ends & buffed them. The connecting rod bolt lengths were measured with a micrometer before & after torqueing. Measurements were more repeatable than my first attempt but still not great. Slight changes in location can produce results that vary by several thousants. It appears that the fasteners need to have the ends ground parallel to produce accurate measurements. In any case here are my results:



Accuracy is likely +/- .001. I'd say the fasteners returned to their original length. Also the force needed for torqueing was very consistent & progressive.
Charles

Online Rough Edge racing

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Re: Replacement Rod Bolts
« Reply #12 on: April 23, 2021, 12:46:30 PM »
Typical bolt stretch is around 5 to 6 thousands inch for a 8-10 mm rod bolt. No matter what, if you care about the engine have the rods resized by a competent machine shop. And have it done after replacing the bolts.
 ARP may have a bolt that will fit with or without a bit of machine work....Most of the time ARP is helpful on the phone...
« Last Edit: April 23, 2021, 12:47:08 PM by Rough Edge racing »
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Offline arbezc

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Re: Replacement Rod Bolts
« Reply #13 on: April 23, 2021, 08:55:15 PM »
Mopartnut,
Effective & simple, bearings would make measuring much more accurate. I didnít realize dimples on both ends for that purpose; I figured it was more for lightening. The replacements sold by MG & HMB look to have a dimple on the threaded end.

Rough Edge,
Youíre spot on, the measures for the 9mm Guzzi bolts fell right in that zone. Iíve heard of resizing connecting rods but donít know much about it. New bolts should be installed beforehand - are the bearing shells chosen after the resizing process is completed?
I see you have a couple of land speed bikes. Bonneville? Those events must be one of the ultimate tests of design & fabrication skills. What would you say is the 2 valve Guzziís weakest link at high speed? Valve train?

Thanks,
Charles

Offline lucky phil

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Re: Replacement Rod Bolts
« Reply #14 on: April 23, 2021, 11:59:42 PM »
Mopartnut,
Effective & simple, bearings would make measuring much more accurate. I didnít realize dimples on both ends for that purpose; I figured it was more for lightening. The replacements sold by MG & HMB look to have a dimple on the threaded end.

Rough Edge,
Youíre spot on, the measures for the 9mm Guzzi bolts fell right in that zone. Iíve heard of resizing connecting rods but donít know much about it. New bolts should be installed beforehand - are the bearing shells chosen after the resizing process is completed?
I see you have a couple of land speed bikes. Bonneville? Those events must be one of the ultimate tests of design & fabrication skills. What would you say is the 2 valve Guzziís weakest link at high speed? Valve train?

Thanks,
Charles

It's called closed and honed when the rod big end is resized. A very small amount is machined off the cap and rod mating faces creating a slightly smaller rod bore then the cap is installed and resized back to original dimensions. The shell size is determined by the crank pin size not the rod size as it will be std. I had my Carrillos done by Carrillo themselves as they offer a refurbishment service for their rods. I have another set of Carrillos that some other complete muppet in a machine shop has done and fucked it up along with the crank pin which the idiot machined with a taper on it and the wrong pin radius. There are some seriously incompetent idiots out there. I like the ARP stretch gauge which uses a pointed anvil on one end and ball on the other.
Ciao 
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Offline jacksonracingcomau

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Re: Replacement Rod Bolts
« Reply #15 on: April 24, 2021, 12:54:34 AM »
Slightly ot but might be relevant when searched

Chucking a leg out of bed was not unusual back in the day, why I and everyone I know used Carillos on high rev Guzzis and , of course , why Daytona got them standard.

BUT it was never the bolts that let go AFAIK, everyone I saw broke the rod itself, big end intact on crankshaft.

Makes me think of my Lario, happy at 9000rpm but rods are just production line v65, amazing they take it, seriously ugly looking things. One day"............

Offline arbezc

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Re: Replacement Rod Bolts
« Reply #16 on: April 25, 2021, 09:43:41 PM »
Thanks for all your feedback,
Thereís a consensus that the original Guzzi rod bolts are pretty good. My original bolts don't appear to be stretched & they fit nice & snug into the caps. Since I won't be pushing high RPM, I think reused them & just replace the nuts. They are flared slightly where they meet the rod cap which could reduce torque values.

While searching connecting rod resizing I came across an interesting test comparing stock vs ARP bolts. The author demonstrates the need for resizing by measuring big end. Here's a link if you're interested:
https://www.youtube.com/watch?v=7Lv0jAD9PtE
Charles


 

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