Timing chain guide/tensioner lifetime - PeachParts Mercedes-Benz Forum

JHZR2 · #1 02-25-2004, 04:11 PM

Hi,

My 83 300D has ~218k. It hgas about 3.5 degrees of elongation using the less acurate 'line up the marks on the cam' method. Car runs great, gets great mpg.

One of the indys I take it to said that after 200k, he has seen the chains break, particularly at startup. Since my chain hsnt elongated significantly, I dont forsee it breaking in the forseeable future. maybe at 250-300k if it still is within spec, ill get it changed for the heck of it, just to be safe. I dont see why it wouldnt still be within spec though; I use synthetic oil and drive smoothly on the highway for 99% of my miles.

I am more concerned with the timing chain tensioner/guides. What is their lifetime? I understand that these parts are designed to fail in a safe way, i.e. the chain wont bee overslacked, etc and jump the sprocket or crash valves. But how long do they typically last? Should I consider changing them, even if I keep the chain, or just keep them until I do the chain, as I said, at 250-300k, as general maintenance (I figure $500 at the dealer is a worthwhile investment after the chain has gone 300k, plus if they screw it up, I can blame them for needing a new engine :p).

Any help/info/advice would be really great.

thanks,

JMH

engatwork · #2 02-25-2004, 05:00 PM

is this dejavu or not

If anyone says anything about oil I will remove their post

.

If it were my car at that mileage and I did not know if it had ever been changed I would change it.

I am fixing to tear one apart to go through the cylinder head, seals and gaskets. The car is showing 175k miles which may be a bit optimistic. I have already made up my mind to replace all the chain and rails while it is torn down. This particular car had a real bad cold idle at start up so I am kinda interested in seeing what was up with it.

JHZR2 · #3 02-25-2004, 06:38 PM

My indy said more or less the same thing about the chain. I think he made the comment about breaking at startup because he told me he has seen a few that didnt have damage from valves crashing, just the chain breaking from the torque of the startyer or whatnot... one was apparently his car, so i guess thats why he told me. Plus he has a machine shop, so he redoes heads, etc as a main part of his business.

Im less concerned about the chain than about the plastic guides and tensioner... Ill keep the chain, maybe have a dealer put in an offset key at 5 degrees or so, but not much else. Its just the fact that I have 21yo plastic parts doing an important job inside the engine.

JMH

psfred · #4 02-25-2004, 06:48 PM

The pastic guides get brittle, but this is much more a problem of the V8s, not the diesels.

If you can feel a distinct slot were the outer links of the chain run over the guide, it's time for replacement. This is particularly true of the tensioner rail, since it gets the most wear.

Those slots will allow the chain to vibrate, and the flexing will increase the wear, plus pound on the guides.

Peter

engatwork · #5 02-25-2004, 08:19 PM

Talking about the guide rails - here is a picture of a rail that came out of a 103 engine on a car that was showing around 165k miles. While I had it apart there was no way I was not going to replace this rail. I feel pretty certain that it could have run awhile longer. This is the oil pump chain tensioner rail.

Joe offers a good rule of thumb (in my opinion) about changing at 6 degrees of stretch if you don't want to spend the $$ right now. The furtherest I have ever seen one stretched was at around 7 degrees and it was still running good.