timing CHAIN STRETCH...M123/M110
 

hey there-
wondering about timing chain stretch specs for both the M123 motor in my '82 euro 250 and the M110 in my 280e.
attaching photos of the M123...i think it's showing 5º of stretch at TDC?
is there a way to adjust the tensioner, or it it automatic?
also, is there a good test for the guides and tensioner?

The timing indicator at the cam is not accurate enough to use in this fashion, but I'd replace that single row chain if it had 100k on it. Those motors didn't have ratcheting tentioners and the chains take an extra beating in such a case. The single row chains do come apart.

The m110 double row chains on the other hand have a ratcheting tentioner and a double row and do not come apart.

I agree with the previous post. The cam timing mark should only be used to rebuild the engine after an overhaul. If the car runs with the 5 degrees slack, then I'd check the timing with a strobe light and see if it lines up. I just recently rebuilt the m110 out of a 77 280e. If I'm not mistaken the m123 distributor drive is also linked by the chain.

Even then, my m110 had at least a degree of free rotation from chain slack with a new chain, tensioner, and rails.

I wasn't aware that it was possible to do a doublerow chain swap on the w123 body engines. I've heard of it on the w126 bodies for the early model m116 engines of the 380 sedans.