Quote:
Originally Posted by Brandoch
This is what I believe is a large factor in #1 main bearing failure. After #1 main you have 2 double row timing chains (BMW usually only does single row chains), then the oil pump gear, then that portion that you pointed out, then the harmonic balancer, then the crank pulley driving 2 belts. That is a long distance without being supported with the load of the timing system and the ancillary systems.
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Very good points and I'll add on top of all of those challenges that IMO the main bearing shells are narrow and somewhat small in terms of bearing surface area - especially for an engine capable of such high RPM and high compression. Then there's the start/stop theory mentioned above where the chain tensioners hold the timing chains in tension for about 2 mins before residual oil pressure bleeds down possible causing #1 main bearing wear in start/stop situations shorter than about 2 minutes.
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