Here is a link to some data on the M30 engine used in your car. This engine
uses a timing chain to drive the camshaft. The question of valve
interference is usually only pertinent to engines that use a life limited
timing belt which requires regular replacement in order to avoid engine
Timing chains rarely fail catastrophically and always give a very noticeable
audible warning if they are worn to the point where failure is imminent.
Unlike the timing belts timing chains get longer as they wear and when worn
appreciably they get so long that the chain tensioning mechanism can no
longer keep the chain tight. When this happens the engine will emit a very
noticeable BRRRRRRRR sound as the chains links bang into the chain guides.
This noise first becomes noticeable with the engine idling because the chain
tensioner is driven by oil pressure and the oil pressure is lowest at idle.
An absolutely excellent answer. Shopping a car based on whether it's
an interference engine because the last one you 'grenaded' was one is
beside the point until you determine whether said interference is a
realistic possibility. With the M30 (535i/is), it is not. With the
M20 (528e), it is.
(Been there; done that)
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