Originally Posted by Slowered318
I had it running pretty good last year, the BMW gods shone some light on me. This summer is ticking, rattles and a strange loss of HP. 13 years and a couple thousand dollars has taught me the M42 is relentless with issues.
that is untrue..the M42 is an excellent motor when treated properly. The one theory I have is that oil level must be kept up. because the motor loves to rev high starvation can occur at the top end. And this is where the problems begin. the upper chain guides start to wear and this is where the rattling starts followed by the chain wear and stretching.
I had one that didn't have top end problems but after some 300k the hydrolic timing belt tensioner went and rear crank bearing did also. The only problem with the motor was the front profile gasket which bmw denied is a design flaw.
The rear bearing has a race which through hard down shifting loads up and the crank wears down this race causing slap. the upper side has the race but the lower side doesn't. Bearing companies now make it with both. Again a design flaw. After correcting these issues the motor didn't give me any problems.
Maybe a few hundred bucks in parts and time.
if you compare this to the M20...let the timing belt water pump service lapse and see what happens. in the day....that would have been a 3k job to get the head rebuilt or replaced.
all relative. :-)