Quote:
Originally Posted by rusnak
Sorry for the dumb question, but what causes cylinder scoring? Would this be the same for example on a lawnmower or chain saw? Does this occur more often in the water cooled cars? I can't seriously remember cylinder scoring being an issue in the old days.
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I'm no engineer or expert but I've read up on this issue, so I'll chime in as best I can. Those of you who know more can feel free to correct any details I get wrong.
There are a number of factors that contribute to bore/cylinder scoring: the material used to line the cylinder wall, engine internal temperature, and oil viscosity being chief among them. From what I understand, if the engine temp is high and the engine is run at a high RPM (especially before the oil is properly warmed, which can be exacerbated by the inaccuracy of the in-dash gauge), the lack of lubrication between the cylinder and the cylinder wall can create a friction that creates a "scratch" on the side of the cylinder wall that might not in and of itself be a problem, but as time goes on that defect in the cylinder wall grows. Owners of m97-engined cars start noticing that their car is consuming more oil, and they start to notice the engine running a little rougher and more smoke from their left tailpipe (or that their left tailpipe gets dirtier faster than the right).
This appears to be the cancer of the m97 engine, and is far more common than the IMS bearing failures that plagued the m96 cars. It can also be a problem because it often doesn't get diagnosed until it's too late -- these cars burn a little oil anyhow, and a lot of cars have darker left tailpipes even without a bore scoring issue.
What can one do to prevent it? Don't bring the engine into the top of the rev range before it's totally warmed up (significantly later than the gauge in the dash indicates). Build revs gradually. Install a 3rd radiator and a low-temp thermostat. Use better oil than Mobil1; there are m97 experts out there who will attest that Mobil1 is actually contributing to this issue and advise using Motul or Joe Gibbs oil.
It appears that "cylinder failure" (which is different than "cylinder scoring") is a totally different issue that's affecting more and more m96 and m97 engines as time goes on; this is what my car *might* be showing symptoms of. I won't know for sure until my local shop takes a look, though.