M117 Lower Chain Rails
 

Does any one have any info on the expected life of the lower chain rails and oil pump chain on the later alloy block M117 engines. I have 150,000 miles on my 1988 560SL. I'm considering pulling the engine this winter and doing a freshen up. Clean, reseal etc. I'm wondering how far to go.

The lower chain rails get a lot of oil so wear really isn't a problem. The upper guides have more wear and the drivers side inner guide gets brittle and breaks when the chain flops around. Then the real problems begin. So, take your cam covers off, rotate the engine to TDC 1 so the cam marks are aligned with the notches on the cam tower and read the offset on the harmonic balancer.

Read it here:

http://www.peachparts.com/shopforum/showthread.php?t=185820

new or used parts
 

The bottom rails are a bear to get to. Even if you install a new hydraulic tensioner the chain will wack it occassionally. How'd you like to be slapped by that chain if you were made of plastic? I build oil pressure before I fire off the motor.