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

The engine number is on the block surface behind the left/US driver side cylinder head. Quite a job to peak down there and read it.

Sixto'
95 S420
91 300SE
87 300SDL
83 300SD

The easy way is to look at the air cleaner mounts on the valve covers. On the older 450,500,560 engins, the rubber mount is screwed directly into the valve cover. On the 380,420 the mount is fastened to a bracket which is then bolted to the valve cover.
The reason for the extra bracket on the 380/420 is the 450/500/560 is about 2 inches wider.

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84 500 SEL (307,xxx miles)