Hello,

Seven degrees of chain stretch is not enough to cause this type of severe pinging in my opinion. I have seen engines set up one chain link off (18 degrees) and not have pinging issues. However offset keys are cheap!

This is a fairly low compression engine (8.7 : 1) compared to the later M130 engines (9.5 :1).

Without actually hearing the noise itself I am not sure it is even engine pre-ignition. The cold engine pinging situation really has me thinking it may be something else. Possibly a broken ring and damaged piston?

__________________
Joe Alexander
Blacklick, Ohio
1964 220SE Rally (La Carrera Panamericana someday)
1966 Unimog 404s (Swedish Army)
1969 300SEL 6.3 (sold)
1969 280SL Pagoda
1973 280SEL 4.5
1974 450SLC FIA Rally car (standard trans)
1982 300D turbo (winter driver)
1986 560SEC
1989 Unimog FLU419 (US Army)
1991 300TE (wife)
2002 SLK 32 AMG (350 hp)