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answer "long" (archive)

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Posted by Angus on January 13, 2002 at 14:25:19:

In Reply to: stupid question on rod bearing posted by nathan on January 13, 2002 at 04:45:04:

the rod bearing is a two piece multi-layer insert (copper/lead/antimony)which is in the large end of the connecting rod (the piece that connects the pistons to the crankshaft) . it is a softer material than the crankshaft yet still hard enough to take the abuse given to it by the exploding gasses above the piston , the reason it is softer is so that any foriegn particles in the oil will embed into the bearing rather than stay on the surface and scratch the crankshaft.this bearing will not suffer any harm as long as there is a layer of oil between it and the crankshaft (most wear to the bearings occurs at startup when there is no oil pressure but that is another story) so as long as there is pressurised oil things are fine ,but the S-14 has a cronic oil starvation problem on long high G righthanders (the oil pump has no oil as it all sloshes to one end of the oil pan ie the baffle fix)and as the rod bearings are farthest from the oil supply as far as the crankshaft is concerned they are the first to loose oil supply and will be destroyed due to lack of lubrication, the softer layers of the bearing melt away due to the intense heat build up (friction) leaving the harder steel bearing backing material which then leaves two things which will continue the destruction of the motor the steel backing is as hard as the crankshaft and will slowly machine grooves into it and remove material from the journal making it to small and rough to put in a new bearing and the excessive clearance makes it that the oil that is delivered to that rod bearing cannot do its job as it just runs out.the bmw S-14 crankshaft is nitrided which makes the journals harder than most production crankshafts (expensive procedure )so it can take more abuse than most but even it will be destroyed due to lack of oil!


i read a lot of posts saying that the s14 could get destroyed due to low oil pressure in hard cornerings ie spun rod bearing. so my question is what is rod bearing and how the engine could get destroyed.
thanks for your input





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