1991 420 SEL 130K Miles. Going to do the timing chain and guides thing. I've found several posts on this but no one talks about replacing the lower guide(s). I understand there are one or two chain guides near the crankshaft. How are these replaced? Also, no one ever seems to replace the crank, cam or distributor sprockets. This is standard procedure on any Detroit iron i've ever done. Always replaced as a "set". Why not on a MB?
I was going to remove the timing chain cover to replace the chain and lower guide(s) but I saw in one post where this could damage the head gaskets?
When ever I do something this major I like to replace all the "ya might as wells" when going back together, belts, hoses, etc. I know about the oil rail plastic spargers (thingies) What else would an anal mechanic want to replace?
Does any one know of a thread where all the parts and MB part no.'s are listed. This would be a huge help when planning/ordering.
Thanks in advance.
Dave

Hi, Dave, I changed my timing chain and the two upper plastic guides, the guide for the tensioner and the tensioner. I had about 8 degrees of stretch at 147000 miles and the engine ran fine, but I was afraid it would wreck after reading in this and other Mercedes-Benz forums. The two main danger areas seem to be (1) the upper guide on the driver's side: the end can crack then break off and get between the chain and the cam sprocket, and this wrecks the engine; (2) the chain can break and ball up in the front cover, plus the valves hit the pistons as this is an interference engine. You don't want either of these to happen. Lots of people seemed to be changing only the top parts and leaving the cam sprockets and the crank sprocket and lower guides in place. I barred a new chain through by connecting it to the old one. It restored the timing to the correct figure without the trouble and expense of going into it to replace the lower parts. I figure at a rate of 5000 miles in 4 years, I'll never hurt it anyway, but my cam sprockets all looked almost new, and my engine was very clean inside. I did change the plastic parts on the cam oiler tubes and cleaned the tubes out, and replaced the thermostat and all the associated coolant hoses; there is one short hose back there that would be a b**** if it went bad. Also you might need to replace the injector seals; no biggie as these are put of the way anyway; I bought a valve-spring compressor (special for this engine) and removed the rocker arms which made the barring of the engine easier and safer for the valves in case I got it out of time; you need to put them back where you found them. There is lots of good advice on this and other forums for this job; read and study them and you can do it, don't be afraid just take your time, be careful, and check and check again to be sure it's right; any questions, don't guess, ask. A local independent shop asked me $650 plus parts to do this; I figure it would have been close to $1000 total for them to do it. I only paid $2000 for the car from the original owner, and I had known the car since new.
Remember to use all three parts of the master link for the new chain; I almost didn't and I was scared when I realized how close I came to putting it together this way. When you start it up and the timing is perfect it will be most satisfying. I am only an amateur Mercedes-Benz technician, but it went fine for me.

Check your lifters, and especially the passenger side cam.

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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D

Dave:

Being bathed in oil all the time, the lower chain rails have an "easier" life than the upper rails and are generally considered good for 350,000 miles or even more. Pulling the front timing case cover is a major job that can indeed result in damage to the head gaskets and create leaks if not sealed back up correctly. Don't go there until you really need to.

However, it is worth replacing the cam sprockets when you do the upper rails, for they receive much less protective lubrication at that high elevation and wear out faster than the other sprockets. New cam gears will further improve your valve timing (I see an extra 1-2 degrees at the crank) and should extend the life of your new chain. Some after-market cam gears can become very "pointy" and I personally like to replace them and the chain every 70,000 miles. If you use all M-B parts you can probably extend that interval, but for me the relatively low cost and vital importance of this job militate in favor of early replacement.

Since you will be removing the alternator to access the rail pins, this is the perfect time to replace your voltage regulator and all the belts. Take a look at the back of your power-steering pump and check it for leaks; the rear seal isn't too hard a job.

Whatever you do, make sure you have enough vise grips and/or heavy-duty cable ties to keep the chain attached to the cam gear at all times during the winding-on process.

Thanks to all. Want to use all genuine MB parts. Can anyone recommed the best and cheapest site to order from?

Randy:

The small hose in the back you mentioned. Is it a heater/radiator or vacuum hose?

Thanks, Dave

Hi Randy I have a 420sel and I am up for the timing chain replacement . What is the best tool to remove the pins which hold the plastic guides and at what stage of the timing chain replacement did you carry this out? I have replaced the chain on my wife's 230e (4 banger) but did not look at the guide proposition on her car.Regards to every one from OZ

Do yourself a favor and upgrade to the Meyle aluminum backed timing guides.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Here's a link to my posting on this very subject.

Chain Guides Replaced

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Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.