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  #1  
Old 12-23-2003, 11:00 PM
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Location: Outside Indianapolis, IN
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E420 M119 Timing Chain- Here's my story

I recently finished changing the timing chain in my 94 E420 and would like to share some of my experience and thoughts about this job. It's a long post!

First of all, my car has almost 150,000 miles on it, so I was beginning to worry about the possibility of the chain or guides failing, and the subsequent disastrous engine damage. I had no bad sounds on startup. I do maintain the car fairly meticulously, and change the oil at 1/2 the recommended change intervals (about every 3750 miles) with Mobil 1, and have done so since I purchased the car with 62,000 miles on it. The end result of all this work was that I was amazed that the guides were all in excellent shape, with only very shallow grooves- visible, but could only be felt with my fingernail. And, though I did not test the chain stretch with angle indicators, I had no difficulty slipping the camshaft locks in place, which says to me there couldn't have been too much stretch. I'm glad the job is done, but I'll bet it could have waited another 50,000 miles or more!

In my mind, there are 3 "stages" of this type of repair. One could change the timing chain, tensioner and top rails with very little engine disassembly. I believe, though, that three tools would be necessary- available from Sir Tools. One would be the clamp on guide to keep the chain on the camshaft gears as the new one is thread in, a timing chain press tool (I used one available for motorcycle chains,) and the holding pins for the camshafts (for installation of the tensioner.)

The disadvantage to this is that this leaves all the guides that might be prone to fail in place. From what I've read on this message board, failure of these guides is what frequently leads to failure of the chain, or the oil pump. (This is not unique to Mercedes engines- I've personally rebuilt an old buick engine that had plastic teeth on its timing gears that broke off and caused the oil pump to fail resulting in spun rod bearings- something else plastic in a Honda engine, too.)

The second "level" of this repair is to also replace the tensioner guide rail and the inner and outer guide rails in the heads. I would consider this the minimum level of this repair that I would feel okay about. It adds a significant amount of work, and the need for another tool- also available from Sir tools. This is a small pin extractor tool that allows the pins that hold the guides in place to be pulled out of the head though small holes on it's front side. I also was able to borrow from the local dealer a tool to help reassemble the camshaft adjusters which have to be put back together under spring pressure. You'll also need a very high quality torx driver in the T27 size to remove the camshaft gears.

This level of repair requires that the poly belt, its tensioner, power steering pump, distributor caps, rotors, front head covers, camshaft adjusters, maybe also the air pump be removed, roughly doubling the time involved.

The third level is to also include the final guide rail in the timing cover on the driver's side. This is what I did, and it involves an almost insane amount of work. This requires that the front timing cover be removed. I believe that I must have printed out about 20 separate repair operations from the CD repair manual (maybe more.) I'm sure that I put in about 40 hours of work over 6 days- not much sleep that week!

This level requires that the radiator, fan, fan clutch, alternator, air pump, power steering pump, air conditioner (these two can be unbolted, but their hoses still connected,) poly belt, its tensioner, water pump and it's reservoir (anybody know what that thing is for?,) fan bearing bracket, harmonic balancer, oil pan (which can just be lowered- be careful with the gasket,) and maybe something else that I've forgotten also be removed. I would hate to imagine what it would cost to pay someone to do this. To any of the techs reading this- is this ever done?

Here are some tips:

The rear bolts on the head valve covers are REALLY hard to get at. Find a friend with small hands and use a 1/4 inch universal joint socket (Sears has them in 1/4 inch drive) with an allen driver bit. This will bend in just the right place- use a little grease to hold the bit in the socket.

Might as well grab some new spark plugs, dist caps and rotors- might also consider new spark plug wires if it's been a while- definitely change the water pump and thermostat, and consider the poly belt tensioner- update it if necessary, poly belt and radiator hoses at the front, as well as the voltage regulator in the alternator. At this mileage, all this stuff should probably be replaced. It all has to come off, and the labor to do it later is significant for some of it. It does all add quite a bit to the cost of the parts. I replaced the chain, tensioner, all of the guides including the one on the oil pump, the oil filter housing check valve, the water pump, thermostat, hoses, poly belt tensioner, and pan gasket, but not the ignition stuff as it had been recently done. This amounted to almost $700 all at least 20% off list price. I spent another few hundred on tools.

The threaded (about $40) pin extractor works great- so I wouldn't bother with the slide hammer type that Mercedes shows in the manual.

I used a flywheel locking device purchased from Performance. It didn't fit quite right, and was expensive at $150, but did work when wired in place. My 1/2" impact wrench running at 140 psi removed the crank bolt on the harmonic balancer fairly easily. This bolt is usually a you know what to remove, so the tool was worth it to me. A loaner puller is available from Autozone to remove the hub after the bolt is out.

The locking pins for the camshaft gears are fairly cheap, and worth it. It would also be handy to have a fairly thin, but large (can't remember for sure, but I think about 24 or 26 mm) open ended wrench to twist the camshaft slightly to get the timing chain to fit exactly right on the gears.

Where any other manufacturer would use 2 bolts, Mercedes uses 6, and at different angles, lengths, head type, etc. They seem to take pride at engineering the crap out of every part. You'll find the most outboard timing chain cover bolt on the driver's side coming down on the outside of the head itself. There are two bolts holding the power steering pump that come in from behind it. Feel around up there from under the car up behind the air conditioner compressor, and over it. An allen headed 3/8 inch drive socket on a short extension with a ratchet will get them. MANY bolts on the air conditioner compressor and it's bracket. Just keep looking. And try to mark clearly where each bolt came from. I thought I could trust my memory- oh boy.

You might get a replacement water pump reservoir as it's plastic pipe snapped right off on me when I tried to remove it.

It is possible, but difficult to replace the oil pan gasket without lifting the engine, by removing all the bolts, and reaching your hand in from the front and sides to tease the old one out and slip the new one in- with the appropriate sealer in the rear (here I used the Mercedes recommended stuff.)

I really can't imagine trying to do this job without the CD manual, but don't use the sealer recommended there. Get the newer stuff recommended by the WIS- it's been posted on these boards by the techs- Loctite 5900, I believe, but Permatex Ultra Black is probably similar.

Enough for now, I'll add more if I remember. Feel free to ask questions.
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  #2  
Old 12-23-2003, 11:08 PM
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Thumbs up

Great info for the archives! Thanks for sharing.
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  #3  
Old 12-24-2003, 02:12 AM
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Good job! I saved it

Any pictures of your E420 with 225/50/16 tires on 16" wheels?
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  #4  
Old 12-24-2003, 07:27 AM
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Look for the post entitled "E420 Euro Sport pics" for pictures of my car.
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(Oh man, this car is sooooo fast.)
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  #5  
Old 12-24-2003, 07:55 AM
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Very good write up Bob.
I have just gone through this same procedure on a 300SE with the addition of the valve guides/seals job too. That crank locking tool is worth every bit of the $$ isn't it. The oil pump chain tensioning slide rail was the MOST worn one in the the car I did (155k miles).
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Old 12-24-2003, 06:18 PM
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Great posting, thanks!
Almost sounds like it would have been easier to pull the motor and put it on a stand where access would be easy...
Comments?
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  #7  
Old 12-25-2003, 01:30 PM
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I have changed the timing chain, most rails (except the one low on the driver's side), and chain tensioner on my 119 5.0L V8. I have spoken to many techs about this and none of them really recommended removing the front cover. That lower rail doesn't have much tension on it and is mostly in oil. Also, the heads rest on the front cover per se and can cause future leaks unless properly sealed up in place. Quite frankly, for the amount of labor involved, there is very diminishing return for pulling the front cover, et al. I would ignore that lower rail.
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Old 12-25-2003, 11:54 PM
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That's good that even at 150k the guides still were in very good condition. I'm never going to change my timing chain and since my car is at 150k I don't think I'll be having any issues with that until 200k. When that breaks I'll buy a new car!
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Old 12-26-2003, 03:31 AM
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I recall a discussion on someone's thought process on the issue of running a 400E until the chain breaks. Are you the fellow in Thousand Oaks or thereabouts?

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  #10  
Old 12-27-2003, 02:40 AM
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Quote:
Originally posted by sixto
I recall a discussion on someone's thought process on the issue of running a 400E until the chain breaks. Are you the fellow in Thousand Oaks or thereabouts?
Yes that is me. Don't get me wrong, I do take car of my car but by the time the chain breaks I will be due for a new car, so the timing will be perfect. LOL
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Old 12-27-2003, 04:04 AM
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That seems like a waste of a car. (IMHO)
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Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

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

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  #12  
Old 12-27-2003, 02:16 PM
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It does seem like a waste of car but I get tried of cars rather quickly, I usually buy a car once a year on average. This car was also rear ended and has not been properly fixed. It will need about 4k in body work to fix it back to spec. Everything works fine and the damage is very minimal so it's not so bad. But if I was to do the body work and the timing chain that would be 6K right there which is a good chunk of change that can be saved for another car.
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Old 12-27-2003, 02:38 PM
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The prosecution grilled zeronero on this matter sometime back and the jury acquitted him. Case closed

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83 300SD
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Old 12-27-2003, 11:08 PM
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Quote:
Originally posted by sixto
The prosecution grilled zeronero on this matter sometime back and the jury acquitted him. Case closed

Sixto
95 S420
87 300SDL
83 300SD
Sorry, I must have missed that case.
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Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

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

ENTER > = (HP RPN)

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  #15  
Old 12-28-2003, 01:03 AM
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Quote:
Originally posted by sixto
The prosecution grilled zeronero on this matter sometime back and the jury acquitted him. Case closed

I pleaded insanity
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