[W126 Coupe] Timing Chain?

[Mike R.]

The concern is NOT the timing chain, they will stretch but very rarely break.  The timing chain guides go bad with age and heat cycling, WILL break, and the pieces generally will be carried by the chain to the camshaft gears, which will result in the cam jumping timing, which will result in all the valves on that side hitting all the pistons on that side, which will pull a minimum of $3500 from your wallet. Yep, it's that bad.

The plastic guides start life a milky white color and end up a maroon color at the end of their life. It's the four upper guides that are the concern. If you know what you're looking for, the tip of one can be seen via the oil fill hole in the passenger's side valve cover. Otherwise pull either valve cover and see what they look like. The passenger side cover is the easiest to remove (no fuel lines in the way).

If your '91 hasn't had them replaced, they they should be done. This is one of those jobs that once you head toward the timing chain guides, the timing chain and chain tensioner should be done then as well. Also, the plastic bits on the oiler tubes above the camshafts are easily accessed and should be done at the same time (they're brittle by now as well). This is a DIY job, with some guidance. 

When I did my SEC chain/guides/tensioner/oiler bits, I did the valve stem seals as well, which were also too hard to function properly. 

While you're doing that much, realize that all the rubber vacuum fittings/hoses on the engine are now hard and create vacuum leaks. Buy yourself a couple of feet of vacuum hose, "Y" & 4-way vacuum fittings, and replace everything you can reach. This is a bit of preventative maintenance that will pay dividends later. Also verify that the upper radiator hose is very soft and supple, otherwise replace it before the upper radiator neck breaks from being shaken by the engine. Check your motor mounts too.

Later,
Mike Ramay

  ----- Original Message ----- 
  From: Peter Weiss 
  To: mbcoupes at mbcoupes.com 
  Sent: Sunday, June 08, 2008 6:02 AM
  Subject: [W126 Coupe] Timing Chain?


  I have a 1991 560 SEC.  It has 48K miles.  Perfect mechanical condition, books and records since new.  All original.  (Paint 7 Interior 9.5)   I have heard rumblings that despite the mileage,  replacing the timing chain on cars of this age is advisable.  Thought somebody out there might have some similar experience.  Thank you, Peter   pdweiss62 at aol.com  


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