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Originally Posted by rjdnyy224
Very informative and interesting (and mildly scary)! I'm glad you came on here to share your experience rebuilding this engine.
This goes to show again how important it is on these engines to get everything up to temp before revving it out at all, and doing oil changes every 5k consistently. Kind of surprising BMW built this engine with such low tolerances/clearances too, it's not like this is an S series engine...
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This also makes me wonder if atleast some of the failing timing chains are caused by this. When scored cam is harder to turn the chain will eventually fail. A new chain would still be capable of turning the cam but for how long?
This theory requires that mild scoring in cam would only cause mild increase in needed force, I mean kind of linear response. So if the scoring is not bad enough for actually preventing cam from turning but is bad enough to cause additional stress on the chain then we might finally got some insight on what causes the timing chain to fail in some of the N20's.
I will atleast keep changing my engine oils more often than what BMW suggest. In Finland the oil change interval is actually 30000km (~19000miles) or 2 years. That is quite a lot and I have followed the 15000km/1 year interval. Maybe that is too much as well, I don't know?
What comes to tight tolerances, I guess one reason is to keep fuel consumption as low as possible. So it's easier for oil pump to pump oil in small volumes for small diameter oil channels. In the other hand, it's harder to get oil to flow in narrow channels, so I don't know if my theory actually flies.