Cranks and rods. you need to know this!!!!

[The Ring-In]

I recently pulled down a motor with a mild cramk failure with the intention of repairing it.

the engine had just started to make noises and was shut down and set aside for repair.

here are the pictures of the crank. you can see how one big end has started to wear down.




the matching rod has wear too where the bearing shell has been moving around.



The backs of the bearings from the rod that didnt let go.




this is the repaired crank and rods.









I regularly tell anyone who has had a problem to have their rods "resized".

this is a reconditioning process where the rod mating faces are ground down and the hole remachined. this restores the size, the roundness and the surface finish. they are also crack tested and checked for straightness and alignment.

All these factors are critical to the operation and longevity of the engine.

when I took these rods to the reconditioner he informed me that the good rod was 2.5thou oversize. that is the tolerences set for the hole were not met and the hole was too big, even tho the rod had no wear on it. the bearing shells had started to fret on the back surface and would soon pound out too.

so they resized them correctly.

This set me thinking so I pulled out some other rods that I have from engines that were running well and in good condition.

guess what they all measure too big. but not by quite such a large margin.

the point to be made here is that with out careful measurement you cannot assume the rod is good even tho it may look perfect.

how do this affect you?

Simply put the bearings rely on the hole being the correct size to ensure it is properly supported in operation. if it is too tight then the bearing distorts and will fail from rubbing on the crank. too loose and the bearing can fret on the rod and will wear itself loose.

The rods I tested were not going to supprt the bearings to the margin set by the manufacturers and this may well be why the have failed. Or may fail in the future.

So ladies and gentlemen I repeat again . If you pull the engine down get the rods resized as a matter of course. its great insurance.

BTW this crank has been ground down .25mm and will be fitted with Honda car bearings.

[Oholiab]

I have not had that problem, but if I have to do a crank in the future I will resize the rods as well, thanks for the info and I am glad you got to it before you spat a rod, Bob.

[zippytlsr]

now ya tell me!!

thanks for the info...

so who/what shop reconditions rods?

[pd]

2.5though is a hell of a lot , there would be very little crush on the shell.
Ill measure sum TL & SV rods when I get home

[Jeff]

Originally Posted by zippytlsr

so who/what shop reconditions rods?

Any shop that remanufactures engines or that does machine work for folks who do should be able to do it. I'm even more inflexible on this than Stu. I've rebuilt many an engine since the first one 37 years ago and every one of them has had the rods reconditioned. I would not consider putting a new engine together without reconditioning the rods.

[zippytlsr]

Well.. that is good to know... i will have to call some machine shops locally... dunno if any of them actually do that kind of work here... ya know.. i live in the sticks and all.

Just wish i had known about it before i had put it all back together...

[cyclecamper]

So though this measuring and resize is normal during engine rebuild and we expect elongation and of course enlargement of the big end hole after the pounding of a big end failure...it sounds like some of the TL big end failures may be due to elongation and enlargement of the rod big end?

Upgrade to SV1000 rods. Stronger at the big end and squared corners at the big end bearing hole. Only $115 US each from RonAyers.com. Then use SV1000 bearing shells (wider but fit TL crank).

I put in Carillo, but that's more expensive and still has the TL-style chamfered edges at the big end hole.

cryo treat if you have the time and money.