Engine bearing failure

[dirk589]

Hi guys,
I have a bearing problem that puzzles me for some time.
Engine is a 1900 cc racer based on MGB block.
After 4 races the conrod bearings look like being damaged by detonation(slightly crazed surface,leading to cracks when not replaced). The puzzling thing is that both top and bottom conrod shell look exactly the same.The crazing covers the whole bearing evenly
My local rebuilder said immediately:local overheating
I have always run on 10-60 full synthetic oil.
More puzzling is that my English friend who races the same engine now has the same problem after switching from Castrol B353(a 40 straight racing oil) to 10-60 synthetic!
Bearings are 3- metal;so highest grade.Crank is billet steel plasma-nitraded.
Is it possible that the oil is too thick,causing not enough cooling on the crank taps? There is no sign of any overheating on the shells.Crank is perfect.
Dirk/Antwerp

 

[MikeHalloran]

Now you have two data points that suggest 60W oil might be too thick at racing temperatures.



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

Why run 60 weight.

Do you have large clearance.

What direction is the final linish done. ie, does it lay the grain away from direction of rotation.

You say trimetal, so they are the best. There is a lot more to bearing quality than number of layers.

It may be heat or it may be fatigue.

Have you checked out the clevite site.

http://www.engineparts.com/pubs_detail.asp?c=2&id=55.

They also have some data of bearing design detail and application. i can't find it quickly now.

Regards

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[dicer]

Do you have any photos?
I'd go with the SAE 40 depending on clearances.

 

[dirk589]

Thanks for reaction,Pat.
The engine is a DOHC with a lot of gears and chains. I went to 10-60 oil to save the gears as they are unobtainable being late fifties design.I always thought that clearances were greater in those times as well,hence.
The clearance is about .002".Tap is 2.1" diameter.
I cannot tell about the crank finish,but the manufacturer is Phoenix in GB which is a reputed one.
I chequed the Clevite and other sites but could't find an answer there. You are quite right that there is a lot more involved in bearings,but we have to work with what we can find here. You Americans are spoiled with all the choises!
I have made a picture of the shell but the damage does not show. Under a magnifying glass one can see that it really is confined to the surface layer.You cannot feel it so indentations are smaller than .002"?
I would fully agree that detonation might be the cause(surface starts to flake off) but would't that in the early stages being confined to the upper bearing half?
Thanks guys,
Dirk

 

[MikeHalloran]

Did you ream out the squirt holes that feed the gears? Or do something else that would change the oil distribution?


Mike Halloran
Pembroke Pines, FL, USA

 

[dirk589]

No,nothing has been changed.My engine runs the normal oil pump,whereas the other has an external belt driven pump that gives even more pressure.
I am convinced thanks to Your reactions that the oil flow is being interrupted momentarily somehow. I will reinvestigate clearance and drive with 10-40 or 10-30 oil to see what happens.Maybe the combination tight clearance/thick oil is the reason.
Thanks for Your reaction-will keep You posted on results.
Dirk

 

[bigpaul]

Hi although you state that you are using trimetal bearings,
I suspect as its MGB based that they are infact A material
sinterd ali, which have a much lower load abilty and poor imbedabilty. With lead overlay Bearings hard to find try one of the new matrials like aluglide 810 an aliminum silicon bearing,
which have a substantial load bearing abilty compared to A
matrial,I also suggest Valvoline V oil it was used in Cosworth DFV and was formulated because of the gear drives.