1986 420 SEL with dubious history and mileage...but runs fantastic....until yesterday when I started the car and got a slight rev and then a chain grind type noise and the engine shut down.
Upon careful restarting, I seem to have a missfire and a selection of noise from the left side front valve cover.
I am assuming the worst, until I get this valve cover off.
An MB mechanic friend stopped by and remarked on the 560 engine in the car...is there a way to positively identify a M117 engine from a M116?
Where are the serial #'s located et all? Other visual cues?

Thanks in advance