Never did get a straight answer, but our assumption was VANOS, as that was replaced along with the engine, and they couldn't give us any other explanation.bluestreak56 said:What was the reason for the replacement engine?
Engine strip-down only showed a small chip in the top of 1 piston, but they couldn't explain why that would cause the 'slight misfire' that they couldn't rectify, and they ended up asking BMW for a new engine instead of spending days & days stripping it down to investigate properly.
I know one wasn't due to abuse, as I've always maintained & cared for my ///Ms. Always warmed up before going beyond 3000rpm, then a little hotter before going above 5000rpm, and up to normal temps before going any where near 7000rpm.
The new engine even had a self-induced 5000 mile running in period, after it's 2nd running in service 1000 miles post-engine change..

