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Wednesday 18th April 2012

Since Monday, when bearing material was found in the sump plug when changing the oil, the engine has been pulled from Big Red and disassembled. On discovering the bearing material, at first, only the sump was pulled to ascertain the extent of any damage. But, after taking off #7, #6, #8 then #1 big end caps and all showed various degrees of damage, the engine had to come out. The big end bearings which failed came from M... and were semi-finished shells which were then machined to fit. Wade isn't happy because the same thing happened previously following the original engine rebuild. Why is it happening? Is it the bearings? Most probably. Is it the machining, balancing and other work? A possibility. Is it the assembly? Not very likely. What other factors could be at play? Thoughts? Opinions? Insights? Anything? Wade is weighing up his options and has been talking to Barry Smith and his engine rebuilder in Tamworth, who rebuilt Barry's V12 with excellent results.

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Yikes!! Sorry to hear.

shorthand notes of some thoughts

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Bearing shells consist of different materials that become softer, going from inside to outside, often starting with bronze as a base up to the babbitt (alloy) as the bedding-in layer. The babbitt surface is paper-thin. When disambled after reaching the end of lifecycle the coppercolored bronze of the base often gleams through. Who machined the shells?

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In the knowledge that Wade is a master of his trade and Mal a partner extraordinaire it isn't easy to speculate. How about the axial clearance of the crankshaft and your way of accurat determination? As you know the gauge must be solidly connected to the cylinder crankcase and its tracer should touch the crankshaft edge, the pulley or the flywheel (sorry for making a virtue of the obvious). When moving the crankshaft with some power in axial direction even minor deviations are visible unless the dial gauge is inaccurate. Once I tried to challenge a sprint record with the use of an inaccurate stop watch.

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The play of the crankshaft sliding bearings influences the oil pressure. The smaller the play, the higher is the pressure. Therefore the oil pressure is useable as an indicator for the play of the crankshaft bearings. Did you observed particular divergences in recent months or even right after engine rebuild?

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Last but not least the oil quality comes to my mind.

The oil temperature should not be forgotten to mention which may causes a discontinuity or even break down of the film of oil on the inner surface of the shells. To open the attached list of mugshots takes some few seconds.

Wade & Mal, chin up, chest out.

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Gerd,

Thanks for your thoughts and the reference material supplied. I'm sure Wade will find them useful in his search for the cause of the bearing failure.

Mal,
Not sure of the exact url addy but Clevite bearing has a number of pics of failed bearings with explanations. Search for Clevite bearing failure and you will find it. Pass the info on to Wade and make a conclusion. Such a shame labor wise...
Jim

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Mal, --> this way please.
Thanks Jim!

Thank you both Jim and Gerd, I'll make sure Wade is aware of this resource.

Jim, to literally "read" bearing shells seems to be a great work method. I hope that BigKev will agree to include this article in the How-To's & Tech Tips. Future generations will call us the bearing shell whisperers.

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Posted in the How To section.