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ChrisBennet ChrisBennet is offline
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Join Date: Aug 2001
Location: Nashua, NH USA
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Originally posted by Nitrometano
I split the crankcase yesterday and found that the first main bearing (at the flywheel) and the nose #8 bearing are worn. The other main and rod bearings looks tired. The drive shaft bearings are totally worn, you can see the cooper. The layshaft it self don't look good at all. The wrist pin bushings at the rods are worn too. I will replace all that parts wit new parts. The next wheek I will take the crankshaft to the machine shop to make a micropolish (or grind it to use oversize bearings), a knif-edge modification and balancing (include flywheel, rods and pulley) When I found the pistons I will balance it and make the half mooning to the cylinders.
Try to avoid grinding the crank if you can. Unlike a "normal" crank, it's hardened and getting it rehardened is a bit of a pain.

The layshaft bearings and the thrust surface of 1st main bearing seem to wear a lot faster than the other bearings for some reason. The ones I have seen usually have copper on those bearings even when the other bearings have plenty of life left.

#8 bearing can often be reused. I don't reuse them but it is so common that main bearings sets don't include #8 usually (unless you buy them from the Porsche dealer). It sounds like your motor either had a hard life or has a lot of miles.

I also think (and I'm no expert) that knife edging the crank and doing the airflow mods is a bit overkill on a (relatively) low RPM dry sump motor but life is too short to try to make everyone else happy. Build your motor the way that makes you happy.

Good luck with your project.
'80 911 Nogaro blue Phoenix!
'07 BMW 328i Coupe
Old 06-01-2005, 02:17 PM
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