E24 635CSi timing chain rattle on cold start,how worried should I be?
The M30 engine in my 635CSi has developed a slight rattle for the first 10 seconds after a cold start. It goes away completely once the oil pressure builds. I've been told it's the timing chain tensioner not holding pressure overnight. Is this urgent or can I live with it? The engine runs perfectly once warm.
The M30 timing chain tensioner is hydraulic and they can bleed down overnight as the seals age. A 10-second rattle on cold start is early-stage failure. You've got some time but don't ignore it. The tensioner replacement is about $200 in parts and 3-4 hours labour. If you leave it until the chain skips a tooth, you're looking at a top-end rebuild. Budget for the job in the next few months.
same issue on the m50 in my e36. the chain tensioner is a wear item on all bmw straight sixes. get it done before it gets worse. the rattle duration increases as the tensioner deteriorates and eventually the chain will jump. its not worth the risk on a nice car like a 635.