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  #1  
Old 04-09-2009, 09:02 PM
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Join Date: Mar 2008
Posts: 98
420SEL: replacing timing chain guides

I have an '87 420SEL, and it's about time to replace the timing chain and guides. I have read all the threads about this job that I could find, and unfortunately I'm still confused about the chain guides.

How many chain guides are there, all together, and where are they located? Which of them actually need to be replaced? Only the top ones on the cylinder head? Which guides do you need to remove the timing cover to replace?

Thanks for your help.

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  #2  
Old 04-09-2009, 10:08 PM
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Join Date: Aug 2003
Location: Phoenix
Posts: 3,726
The MB service CD for the 126 body is only $20 + shipping. It's part # P-2700-126-099.
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  #3  
Old 04-09-2009, 10:16 PM
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I already have the CD, but it just doesn't explain, in a cogent or understandable fashion, the questions I asked. I also have an AllDataDIY subscription, but neither does it explain guide replacement in detail.

And, as I said, I've read all the threads on the subject, but my questions remain unanswered.

Therefore, I'd appreciate it if somebody would answer my questions. Thank you.
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  #4  
Old 04-09-2009, 10:49 PM
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Join Date: May 2006
Location: Birmingham, Michigan
Posts: 58
Timing chain and guide replacement

Here's a very good step-by-step explanation from Benzworld.
I can't really comment on how accurate it is because I have never done it, however other members have said it was great. Good luck!

The new timing chain, upper chain rails and tensioner are finally in the 1989 420sel with 98Kmi. This report summarizes some thoughts that might be useful to a first-time DIY'er.
A. This job took at least twice as long as I thought it would, and that didn't include time studying the manual and other sources. If you are in a hurry or do not enjoy the work, this may not be a job for for a DIY'er.
B. Information--Search the List archives for useful information. Especially useful threads were "timing chain and rail replacement questions for a 117 engine" (Nov. 28-30, 2004) and "420sel timing chain" (October 29-30, 2003). I also bought an illustrated booklet ("preventing catastrophic V-8 engine failure") from **************.com (no connection) and this explained most of what the manual does not. There are photos of the "3 vice-grip method" of chain replacement at Mercedesshop.com ("M116/117 timing chain replacement"). Also, the recent book "Mercedes Benz Technical Companion" has several useful articles on timing chains and chain replacement.
C. The manual is essential reading of course, but I found several possible discrepancies. First, the camshaft sprockets should (must?) be removed to replace the upper chain rails. Second, it appears possible to wind in a new chain without removing the right side rockers. I did remove them, as recommended, to eliminate the problems of the right cam possibly jumping time. Third, I used a bit less than the manual's 25nm of torque on the 8mm bolts that attach various parts to the heads. The 1991 Technical Data Manual seems to indicate 21nm of torque for most of these. Also, I left the old tensioner partially inserted in the right head (held with a long 8mm bolt and nut arrangement) while winding in the new chain, so most of the slack on that side of the chain would be taken up.
D. Unanticipated problems--the 4 left-side chain rail pins were more or less rusted inside. A 6mm bottom tap cleaned them up. All 6 pins came out relatively easily after soaking in Kroil. I also "chilled" them with Radio Shack component cooler, and that might have helped. I bought 4 new pins. An old pin is the perfect drift for replacing the pins recessed in the heads. One of the cap screws holding the alternator mount on the right head was corroded and I bought a new one. The distributor retaining bolt was hard to get out. That bolt goes down through a 2-inch long spacer under the distributor and you need to get the Kroil down in there. Remember to counter-hold the fuel line fittings at the fuel distributor when disconnecting the fuel lines. Be prepared for a minor fuel spill. Relieving the gas tank pressure at the gas cap may alleviate this.
E. Other jobs--While the front of the engine is clear, it is easy to replace the thermostat, the radiator hoses and the voltage regulator. (Mine were original and due for replacement.) Also, with the top radiator hose off, the fan shroud can come out making it a little easier to work on the front of the engine.
F. Parts--I used genuine Mercedes parts (chain, rails, tensioner, oil tube kits, valve cover gaskets and bolt washers). There are reports of aftermarket rails (and chains) failing relatively quickly. The new chain came with the "fish head" clip on the connecting link favored by Stu. (The clip must be installed so that the "head" points in the direction of chain travel.) I replaced the tension rail lining (available from MB as a separate part) and re-used the tension rail itself. I did not replace the cam sprockets, which looked fine.
G. Tools--Nothing truly exotic is required. A special valve spring compressor if the rockers are to be removed, a good 6mm hex bit socket, and a tool for pulling the chain rail pins. For the latter I ordered online a few long, fully-threaded 8.8 strength 6mm bolts, nuts and fender washers from the Bolt Depot (again, no connection), and used them with various sockets, large nuts, shim washers, etc. to replicate the official pin puller tool. The websites of Assenmacher, Zdmak, etc. illustrate the factory tools.
H. Although there may be some short-cuts, my order of battle was as follows (refer to the manual and/or the ************** booklet for the job procedure details):
1. Disconnect battery. Remove air cleaner. Remove fan together with visco fan clutch (store in upright position), leaving 1 bolt in the fan pulley. I used a strap wrench on the pulley hub to keep it from turning. A long 10mm box wrench is helpful.
2. Unbolt the cruise control actuator and put to one side. Remove alternator and then alternator mount from right head.
3. Remove spark plug wires from plugs. Remove distributor cap together with plug wires. Set engine to TDC. On the engine, mark orientation of the distributor mark/rotor so the distributor can be replaced in the same position. Remove distributor.
4, Unbolt P/S pump and tie off to the side (the hoses remain connected). Unbolt P/S pump mounting plate from left head.
5. Disconnect fuel lines at fuel distributor and tie up out of the way. Remove valve covers. Gently pry off oil tubes and clean any plastic bits out of the cam bearing towers with picks and tweezers. If you are going to remove the right side rockers, now is a good time.
6. Check 3 upper chain rails for damage. Assuming no broken rails, pull all 6 chain rail pins 1/4 of the way out (about 3/8 of an inch). if you are going to have a problem with these, now is the time to know.
7. Slightly loosen both cam sprocket bolts. Reset engine to TDC and confirm/evaluate camshaft timing.
8. Mark and remove left camshaft sprocket, keeping tension on the chain (I used 2 bungee cords with hooks suspended from the garage overhead). Pull pins and fit new left side chain rails, one at a time. Refit left sprocket, observing marks, and the bolt.
9. Remove old chain tensioner. Mark and remove right camshaft sprocket, keeping tension on the chain. Pull the 2 rail pins and remove the old right side chain rail. Remove tension rail, replace lining, and refit the tension rail. Fit new right side chain rail. Replace right side cam sprocket, observing marks, and the bolt. (I deferred retorquing the cam sprocket bolts in case the timing needed to be adjusted after the new chain is in.) Reconfirm camshaft timing.
10. Wind in the new chain using the 3 vice-grip method or, with an assistant, using the method in the manual. It is easier if the spark plugs are out, but I would remove them only if new plugs are going in.
11. Fit new chain tensioner. Double check camshaft timing. Torque cam sprocket bolts to 100nm.
12. Put everything back together in reverse order. Use new oil tube kits and valve cover gaskets. Remember to set the distributor timing precisely according to the manual (before installing valve covers to make TDC identification easy). Do oil and filter change.
The main thing is to work patiently and carefully, and always use shop rags, etc. to prevent anything from falling into the engine. Be especially careful with the timing chains, as it would be a disaster if a chain fell into the engine.
All in all, the job was challenging and fun (and successful), but time-consuming as constant vigilance is necessary to avoid an expensive mistake.
At 98Kmi and 15 years, the old chain and rails were in OK shape (right cam retarded about 5 degrees), and didn't yet make noise on start-up. They probably would have gone a few more years. The plastic oiler tube clips were very brittle and definitely needed to be renewed.
I hope this report is of some help to other W126 DIY'ers. Thanks to Stu, Bob and others for their helpful advice. Charlie Wagner, 1989 420sel 98Kmi.
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  #5  
Old 08-01-2012, 08:11 PM
macdoe
 
Join Date: Sep 2007
Location: Canada
Posts: 759
Hello, I can't seem to get the timing chain tensioner rail bearing pin out. I have tried hooking it with a nail...a bent coat hanger...a cant bolt like the manual says. I think it is turning but will not pull out. Is there a trick to it? I have tried pulling while moving the rail around. I sure am not pulling the timing cover. I have a new rail with new lining and the top guides to go in and am stuck here. Thanks
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  #6  
Old 08-01-2012, 08:44 PM
macdoe
 
Join Date: Sep 2007
Location: Canada
Posts: 759
why would they not thread the inside of this pin for a bolt like the rest of the pins we took out, which were in a dumb spot as well. A cant bolt is actually described in the service manual....but if it is in an aluminum block it won't take much and the threads for the plug will be buggered. I do not like this car.
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  #7  
Old 08-01-2012, 08:49 PM
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Join Date: Jun 2011
Location: Las Vegas, NV
Posts: 348
Heat the timing cover around the pin with a heat gun, then try to pull it out.
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  #8  
Old 08-01-2012, 09:05 PM
macdoe
 
Join Date: Sep 2007
Location: Canada
Posts: 759
o.k I will try that. Thanks
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  #9  
Old 08-01-2012, 10:11 PM
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Join Date: Feb 2007
Location: los angeles
Posts: 814
Another thing that works is an instrument cluster tool , wedge it in at an angle and pull it straight out or find a bolt and grind it TO A TAPER angle and try to pull pin out
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  #10  
Old 08-02-2012, 12:08 AM
macdoe
 
Join Date: Sep 2007
Location: Canada
Posts: 759
I tried something similar...a piece of the wire handle off an oil filter. The spiral easy out is tapered and has teeth on it. I tried heating the boss on the timing cover with a propane torch. Nothing is working. I am afraid that now that I have turned it, the pin may be getting hung up on something. Do I have the only pin to be stuck on one of these?
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  #11  
Old 08-02-2012, 05:40 AM
macdoe
 
Join Date: Sep 2007
Location: Canada
Posts: 759
Got it out by an eighth of an inch with a spiral easy out....and then used a nail head with small needle nose vise grips and a 3/8 drive extension to pry against on the block. I guess after getting it out far enough to get the lip on the nail head in behind it
The pin that came out had a number of lines scored into it....I guess from the hole in the old tensioner rail. I think that the scored surface of the pin was preventing it from sliding out easier. I used a pin from a spare motor that was much shinier.
Easy instructions on this thread . Thanks for the help.
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  #12  
Old 08-03-2012, 05:36 PM
macdoe
 
Join Date: Sep 2007
Location: Canada
Posts: 759
Hello, we now have three new slide rails and 1 new tensioner rail and lining. I have reinstalled the old tensioner loosely. I am ready to roll in a new iwis timing chain.

I was wondering if the new chain could be rolled in with the old tensioner in place or does the tensioner have to come out? I do have a new Febi Tensioner in a the bag of oil they shipped it in along with a quality assurance claimer. I was going to put that in after the new timing chain is rolled in....but will put it in now before the new timing chain goes in if that is better.

I had one of the pins on the drivers side very stuck as well....but it finally let go and came out.....but not before breaking off a bolt inside the pin, luckily it just threaded back out. I think the bolt I used to draw the pin out was too long and that is why it broke. I used a spare pin from the parts motor. (top inside guide pin). I put a small dab of silicone around the heads of the pins before completely driving them in.

I found the outer guide to be broken just below the boss that the pin slides through. The broken piece was just sitting on the chain....ready to jam things up at any moment. It was far enough down that I had to use 14 inch tweezers to get it out. I am very lucky to have done this when we did. I think we probably saved this motor.
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  #13  
Old 08-03-2012, 11:51 PM
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Join Date: Jul 2003
Location: Tennessee
Posts: 430
very nice! i'm not 100% sure but i think i left the old tensioner in when i rolled in my chain (it was few years ago). i did it by myself and used the vise grips method. i also put a high quality string on the end of the chain as i was feeding it in just in case the vice grips let loose (don't wanna drop that chain in the engine) hopefully someone can chime in about the tensioner to make sure
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  #14  
Old 08-04-2012, 12:27 AM
macdoe
 
Join Date: Sep 2007
Location: Canada
Posts: 759
Also found the distributor cap cracked up to the #3 cylinder contact and had severe corrosion on the inside of the cap on the contact. My son asked me why it was all mouldy.The rotor was all buggered. The #3 spark plug was all wet. I am not sure I was running on all 8 cylinders.

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