Timing chain

[Russell.Nile@nileassociat]

I broke the cardinal rule and rotated the engine backwards during a valve adjustment.  I am replacing the timing chain because I noticed it was worn and discovered that at TDC on the cam the crank is about 1 degree after TDC.  This could be because of the wear on the chain, but I am concerned that I skipped a tooth during the backwards rotation.

Not a big deal to reset the crank and cam if they are off....but if I knocked the fuel injection/distributor off a tooth how can I detect that?

Russell

[Benz Dr.]

Why do you think it's out of time? 1 degree isn't enough to worry about.

[ja17]

Hello Russel,

Dan is correct, one degree is well within specs.  One link equals 18 degrees of timing. So if you jumped a tooth you would be nearly 18 degrees off.

[Russell.Nile@nileassociat]

Benz Dr.; I have no reason to believe it is out of time yet...just fear. 
Ja17: I wasn't so concerned with jumping a tooth on the crank, but jumping a tooth on the fuel injection.  I understood the sprocket after the cam/before the crank operated the fuel injection and distributor and was concerned that I skipped one there (although the distributor still appears to be pointing squarely at piston 1 firing position). 

I'm not even sure how likely that scenario is though.  When I did turn it backwards the chain did not exhibit the kind of looseness that would indicate it could skip a tooth (I had the tensioner installed still).  The only reason I am changing it is because with a little bit of the unload that I had I was able to fairly freely rock the chain links laterally and that struck me as worn.

While the motor could probably use a rebuild a removal/rebuild was not in the budget just yet.  It smokes a bit after resting (maybe guide seals)...some of the cam accessories appear to be worn a bit...lower end hasn't been touched in over 130K of driving (245K total)...but it runs pretty well overall. 

BTW: New chain tensioner = very expensive.  All pieces to re-build the existing tensioner = very reasonable.

[ja17]

Hello Russel,

The special bolt holding  the power steering pump resevoir onto the block (underneath), keeps the chain close to the timing sprocket for the injection pump and distributor. It will prevent the crankshaft and timing from getting out of sink.
Youre timing should be just fine.

Servkice your engine well and you will most likely get many more miles before major repairs.

[Benz Dr.]

Joe is right of course. Contary to popular belief the timing chain on these cars won't jump a tooth every eassily if ever. You would need to have a of of wear on all the moving parts before that would happen.
 
 I had a 280 once with the M110 engine. This engine is a twin cam with a lot of moving parts. The chain is longer on this engine and is prone to wearing out. Rather than a tensioner gear it has a slide rail that can wear making the chain go loose.
As luck would have it, I was going to the Grand Prix in Detroit and the engine suddenly died on the way there. Turned out the chain was so loose it slipped a tooth on the distributor drive gear. I was able to reset it and it ran fine until my ex wife had the same problem. It was towed to MB ( her idea ) and $1,200.00 later I had my car back. This was in 1984 so that was a lot for a fairly simple job.

 One of the many reasns she's the  '' Ex ''  now...........

[Russell.Nile@nileassociat]

Thank you both for the confidence.  I didn't see that there was enough slack for it to jump...but I created that fear when I saw the crank off just that little bit.  It will be interesting to see if it is closer when the new chain goes in though.

Thanks again.