I've just had all the cam followers ('lifters' to you in the US?), timing chain, chain guides, chain tensioner, and rockers replaced but even after 700 miles there is a very diesel-like solid knocking noise on starting from cold that only disappears if I hold the revs at 2000rpm for 20-30 secs. Once warm the engine is totally quiet. Mechanic says the noise is the cam followers and some of the new cam followers must be faulty. Is this likely? Is there some trick to fitting Mercedes cam followers that my mechanic might not know? He says he soaked them in oil for 30 mins to 'prime' them. How do I tell the difference between cam follower noise and chain noise? Oh yes - it's a 1989 W126 (500SEL) with 117 engine. Hope someone can help!