[W126 Coupe] Timing chain and lubrication maintenance note...

[Carl Hansen]

The valve train starving from oil will fly apart as in this case once that happens pistons will start slapping at the valves and big trouble. That engine is history.
I recall in my early days of mechanickering leaning over the engine of an American V8 revving the engine. Boss comes running over; hey Carl be careful that heap's got 120,000 plus miles on it don't rev it like that or you'll jump the timing chain. My old beat up Pontiac station wagon died one morning in the driveway just as I started it up. Just like Bellamy said. I have never seen an engine jumping a timing sprocket on the run.
On the other end of the scale my winter beater a 1989 Volvo 240 is just 15,000 km shy of 400,000 that's about 242,000 miles. just a little 4 cyl 2.3 L engine still goes like stink and never uses a drop of oil. To the best of my knowledge the engine's never been touched.

Carl  
  ----- Original Message ----- 
  From: Mister McGoo 
  To: Mercedes Coupes Mailing Lists 
  Sent: Friday, January 25, 2008 4:49 PM
  Subject: Re: [W126 Coupe] Timing chain and lubrication maintenance note...


  My 2¢...
   
  -Carl is right... that was not likely a simple case of a chain jumping.  That would have wrecked the valves, the cam, and possibly the piston, but there has been tremendous heat there!  I'd question what also may have been damaged by that kind of heat.  It would be alarming indeed to find debris in the other valve cover!  This engine may not be a candidate for rebuilding at all.
   
  - The chain can jump when driving at highway speed.  That, however, is unusual, it more often happens at start-up.
   
  - Attached below is a picture of a worn sprocket.  (I pulled it from my scrap metal pile as an example)  The "valleys" in the sprocket should be almost 180° fitting the chain roller, and the tip of the points slightly rounded.  The shape of the valleys is critical.  These valleys have worn far wider and the tips are worn almost to sharp points.  That why this one is in the scrapheap.  Generally speaking, most often it is wise to replace the sprockets with the new chain unless they really look in good shape. 
   
  -Bellamy






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    Date: Thu, 24 Jan 2008 22:08:42 -0500
    From: plustech at optonline.net
    To: mbcoupes at mbcoupes.com
    Subject: Re: [W126 Coupe] Timing chain and lubrication maintenance note...


    That looks easier than I thought. I was picturing taking half the front of the motor apart. Looks like some patience makes this a pretty low cost/risk job to prevent a lot of damage. Hmmm, better add a few $ for a beer budget on this one.



    OK, so that is the deal with the chain, but what about the sprockets? Whenever I did American cars, I replaced them with the chain, but they did not have tensioners, so make sense. 



    Anyone have history/opinions on the necessity of replacing the sprockets or how to check for wear?



    Thanks for the info. 



    Thank You,



    Alexander Hochhausl, PE

    Tel: 516-909-3794



    1



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