• Ciao Guest - You’ve landed at the ultimate Guzzi site. NEW FORUM REGISTRATIONS REQUIRE EMAIL ACTIVATION - CHECK YOUR SPAM FOLDER - Use the CONTACT above if you need help. New to the forum? For all new members, we require ONE post in the Introductions section at the bottom, in order to post in most of the other sections. ALWAYS TRY A SEARCH BEFORE STARTING A NEW TOPIC - Most questions you may have, have likely been already answered. DON'T BE A DRIVE-BY POSTER: As a common courtesy, check back in and reply within 24 hours, or your post will be deleted. Note there's decades of heavily experienced Guzzi professionals on this site, all whom happily give endless amounts of their VALUABLE time for free; BE COURTEOUS AND RESPECTFUL!
  • There is ZERO tolerance on personal attacks and ANY HYPERLINKS to PRODUCT(S) or other competing website(s), including personal pages, social media or other Forums. This ALSO INCLUDES ECU DIAGnostic software, questions and mapping. We work very hard to offer commercially supported products and to keep info relevant here. First offense is a note, second is a warning, third time will get you banned from the site. We don't have the time to chase repeat (and ignorant) offenders. This is NOT a social media platform; It's an ad-free, privately funded website, in small help with user donations. Be sure to see the GTM STORE link above; ALL product purchases help support the site, or you can upgrade your Forum profile or DONATE via the link above.
  • Be sure to see the GTM STORE link also above for our 700+ product inventory, including OEM parts and many of our 100% Made-in-SoCal-USA GTM products and engine kits. In SoCal? Click the SERVICE tab above for the best in service, tires, tuning and installation of our products or custom work, and don't miss our GT MotoCycles® (not) art on the BUILDS tab above. WE'RE HERE ONLINE ONLY - NO PHONE CALLS MADE OR RECEIVED - DO NOT EMAIL AND ASK QUESTIONS OR ASK TO CALL YOU.
  • Like the new V100, GuzziTech is full throttle into the future! We're now running on an all-new server and we've updated our Forum software. The visual differences are obvious, but hopefully you'll notice the super-fast speed. If you notice any glitches or have any issues, please post on the Site Support section at the bottom. If you haven't yet, please upgrade your account which is covered in the Site Support section or via the DONATE tab above, which gives you full site access including the DOWNLOADS section. We really appreciate every $ and your support to keep this site ad-free. Create an account, sign in, upgrade your account, and enjoy. See you on the road in 2024.

con rod bolts: replace or reuse?

jbu

Tuned and Synch'ed
Joined
Oct 25, 2010
Messages
30
OK folks, what do you all think, do I have to replace the con rod bolts each time or can I reuse them. Those bolts are pricey and the ones that came off the bike visually look OK.

Joël
 
I do not know about Moto Guzzi bolts but in general I would buy new ones - too critical part to spare costs.
I think they are supposed to be extended a bit when properly torqued and they do not go back to their original length after they are disassembled. If reused they will be extended a little more loosing in rigidity which may be an issue on the long run.
 
While plenty of people do re-use them I strongly advise against it. They are one of the most highly stressed components in a motor and while not a 'Torque to yield' item the Guzzi bolt are difficult to measure accurately for stretch and are actually torque specified. Nuts are fine. I always replace bolts though. The consequences of a bolt failure are not pretty or cheap. I'd also suggest getting the rods re-sized if the motor is apart.

Pete
 
Aw come on! these are not the responses I want to hear. Replace bolts, rods resized? really? what exactly does that mean? I respect what the experts have to say, so I will listen, even when it hurts.
keep it coming I'm a glutton for punishment.
Joël
 
Because of the stresses imposed on the connecting rods the eyes will have a tendency to ovalize, especially if the motor is used hard. A hydrodynamic, 'Slipper' type bearing relies on there being a very close and even difference in size between the journal on which it runs and the bearing/bearing material (In this case the shells in the rod.). The 'Rule of thumb' is 1 thou of clearance for every inch of journal diameter.

What allows a plain bearing to work is not that the oil is 'Slippery', it's the fact that as the bearing spins on the journal a hydro-dynamic wedge is created in the film of oil within the bearing. The closer the clearance, the greater the strength of the wedge and it is this that prevents boundary lubrication, (Bits rubbing together!). As with most things in the engineering business the exact clearance required is a trade-off. Too small a clearance and insufficient throughput of oil means the bearing will overheat. Also as the clearance is decreased the internal friction of the oil may overcome the friction betwixt the back of the shell and the rod forcing the bearing to spin. If that happens the clearances all go to hell in a handbasket and it makes the 'Dogga-Dogga' noise. If the clearance is too big though the oilwill not be able to form the hydrodynamic wedge needed to prevent boundary lubrication and once again the bottom end will make the 'Dogga-dogga' noise.

On any high mileage engine, even if it hasn't suffered a catastrophic failure, it is a good idea to get the rods re-sized as this will ensure not only that the bearings will be accurately circular when installed but also that the contact between the back of the shell and the rod and cap that they are installed in is good. Remember, it's only that 'Back Contact' of the shell established by the nip of the rod, (Yes, that is the correct term!) that prevents the bearings from spinning.

Yes. This may not be what you want to hear. But knowing it is cheaper than blowing up your motor because you don't! It might also be worth remembering that knowing this sort of shit is why you pay a good mechanic/tradesman skilled wages when you take your bike to a shop.

Pete
 
Wow, that's one hell of an answer. I am far from being an engineer so things like hydrodynamic wedges hurt my head. But I thing I understand the gist of what you are saying.
My next step is to have a friend who owns a bore gauge and micrometer measure my rod eyes. micrometers and me go together like whores and priests.
Now, if things end up going my way and the rods are not oval, what about the 2 half shells in the eyes of the connecting rods, do they need to be replaced each time too? I think I know the answer but I need confirmation.

Joël
 
Series4 said:
Replace bolts every time

Exceptions to the truth...?

Carillo offer two types of bolts, namely:
1. "The expensive Carillo bolt" and
2. "The unbelievably expensive Carillo bolt". :roll:

Apparently the latter can be reused. Have I got the information right? (at least I was made to believe that - and went for it).

One more point regarding conrod bolts, there are bolts being sold now by "a big and renown after-market dealer" in Europe, that have caused catastrophic failure in a newly overhauled racing engine for a friend of mine. Bolts were fitted brand new by a competent mechanic. One start to wonder where they get their stuff from some times. There are many statements like "never from there again" being heard among the classic racing folks around here....
 
Far out eh Jbu?

I recently had a regrind done to a racing engine crank. New rod bearings of course, AND new Carrillo bolts ($161 US for 4 bolts!!!).

I ran the bike at Bonneville in August and it ran well. Maybe 10 runs ... so 35 miles or so WOT. I then took the rods out and inspected the bearings. New bearings (advise from Bill Ross) and I inspected the bolts.
The bolts would stretch to proper length within torque maxes. So I reused them.

The bike ran fine in October. 2 runs ... about 7 miles or so WOT.

I have yet to dissasemble the engine but feel I must before I run it again. If the engine had failed, and not killed me, I would have chalked it up to experience.

What I am getting at here is you are in a GREAT position to make your bike more reliable. If you can't take blowing the engine and the huge cost, both dollar and physical, do the right thing.

It may just be that you could get away with reusing those parts... I did. However, would you be able to accept catastrophic failure while riding through the desert?

Also, it sure is a drag to have to remove the engine, rebuild it ($$$) , reinstall it. When you could have avoided the whole exersize.

On my daily rider I try to do everything I can to prevent a bad situation.

You mileage may vary.

Alex
 
Thanks for all the help everyone, it's greatly appreciated. I am learning quite a bit. If you haven't realized it yet this is my first true engine strip.
My buddie came by today with his gauge bore and mic. My con rod are good, nice and round.

the journals on the crank came to 1.7333 which makes it fall into the standard class B category. (don't know what that means exactly)

I placed the new gugeon pin in the bush end and there was a bit of slope, so it looks like I have on my grocery list:
new bushings, new bolts and new standard bearing sleeves.

Joël
 
jbu said:
If you haven't realized it yet this is my first true engine strip.

Then I strongly suggest you take a tour of Pete Ropers series of illustrated instructions on how to dismantle and assembe the big-block Guzzi engine. The files are compilations of a long series of postages that Pete did on the US forum a few years ago. You'll find lot of good tips in the picture texts plus a few words on valves and cylinder heads at the end. More practical than most illustrated books and more fun to read to read the comments!

http://www.thisoldtractor.com/guzzitech ... ctures.htm

rolf j
 
I've never seen a single rod bolt failure on a Guzzi. Guzzi's stock bolts are so ridiculously overengineered, I'm not surprised. Take for example Guzzi's Carrillo application in the Centauro and Daytona- guzzi specifies a bigger ( and heavier...) 3/8" rod bolt instead of the typical 5/16" that come with the Guzzi Carrillo rods I use all the time.

Assuming that they have not been overtorqued or otherwise damaged, I reuse bolts on race motors and street motors regularly.

Ed
 
I guess a good question is, how do you know if they have ever been over torqued, if you don't know the history of the bike? Can you measure the length of the bolt?

For piece of mind I can see shelling the $$$ and putting in new bolts.

Joël
 
Carilos you torque by stretch. The stock Guzzi bolts are tightened simply by torqueing them to 36ft/lbs. Yes, I'm sure that especially on road motors it is probably fine to re-use them. Thing is a failure will result in catastrophic damage and with any T3/early Lemans type motor we are talking about re-using a nearly 40 year old component that has to take some of the most extreme loadings in the engine.

Choose wisely.

pete
 
already chosen. After hearing and reading opposing opinions from people I respect on both sides, I placed an order today for end bushings, bearing sleeves and NEW con rod bolts. I just couldn't handle the stress anymore. It's done and now I can breath easily.

Thanks to all for all the help,
Joël
 
Have we established that these are "stretch" bolts?

All bolts are potentially 'stretch' bolts as long as you can put a micrometer across the length of the bolt unless you mean one time use bolts that know seem the rage in the era of throwaway junk. You may have to finish the bolt ends so you have a nice true length to measure.

Setting the bolt stretch by measuring the bolt length is always the preferred method for pre-stressing the bolt as you don't have to worry about burrs or thread friction causing an inaccurate reading - which can produce a significant error.

The stretch required is (from memory) typically the torque required to give you 90% of UTS.

If you do use a torque wrench always lubricate the bolt with the same lubricant used by whoever determined the torque setting originally. So in the case of Guzzi rods it is probably good old engine oil, with Carillos, oil and moly.

Standard industry practice (at least with Cat where I was trained) is to re-torque the bolts three times to take into account any bedding in. This may be overkill but I have never had a conrod failure resulting from improper torque in 200+ engine rebuilds.

And if it makes you feel better, the last two people I know who didn't replace their conrod bolts against my advice had catastrophic failures (albeit on british iron -Ed is right that the Guzzi bolts are well engineered). In the end it is very cheap insurance - especially if you don't know where they came from and who wrenched on them.

My feeling is the same for valves except for the valves on the falcone that are have stems so oversized they could come from a Cat D9.

Ta,

Chris R
 
Back
Top