Hello all - Our patient today is a 1972 (not an 1971) 300SEL 4.5, U.S spec car.



Here she is:



Usually I'm monkeying around with American "hot rods" but I got it into my head to buy a '71 300SEL and even though it really doesn't fit the mold (Quiet, four doors, no fins) there's something about this car that defies logic, and I find myself pulling it out for a drive, instead of aforementioned "hot rods" but my 300SEL needs a little help and so I come to you for some assistance. The car seems to run "ok" but has a miss and runs rich...and by rich I mean the richest running car ever - I have enough black soot on the shop floor to draw in...not even kidding. I could write "please fix me" in the black dust. It seemed to be doing ok, but then it started to stumble and the idle was terrible - bad enough that I very much doubt it was firing properly on all cylinders.


I decided to give it a tune up, and I figured it was good sense to check and change the timing chain. Upon inspection however, the chain seemed in very good shape - tight, clean, no wear marks on the guides or tensioner, and it had been replaced at least once with a currently available chain (brand stamped into the chain matched my new one) I almost left it alone, but I noted that with the balancer indicator at Zero (0) and the passenger-side cam timing mark aligned, the driver's side looked like this...



Now, not being accustomed to Mercedes, I didn't know if that was 1 tooth off, a stretched chain, or 14 teeth off. So I decided to just try adjust it, given that the chain really did look good...perhaps someone just installed it wrong and jumped a tooth. I took the sprocket off, adjusted the cam (that was fun) put the chain back on the sprocket and then put the sprocket back on the cam (even more fun). everything lined up perfectly. Then I spun the engine around a few times by hand, and ......everything had gone right back to where we started....see picture above. SO...I said, perhaps the chain is stretched after all. I had my wife help with changing the chain - all went well and we got everything back together. I again turned the engine over by hand, and for all our hard work we achieved......(see picture below)



YEP....we achieved absolutely nothing. Its exactly the same, and remember I already reset the cam, so technically everything should have been right on the money.

So here is my question..... does this actually matter? Aside from being less than factory prefect, is this going to be an issue? I'm looking to have the car run well, but I'm not looking for every ounce of perfection...it is almost 50 years old. For the sake of completeness, here is a picture of the passenger side at the same moment - note the alignment. ...Also note that someone appears to have scribed their own timing mark?...wasn't me. I know ideally both cam timing marks should align, but its not that far out - perhaps half the width of the timing mark - not sure what that means in degrees.




Valves need adjusting, and I have tools coming for that. I'm also going to replace all the injectors and the fuel pressure regulator - fuel pump and filter already replaced.



Thanks,