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supergirl 05-16-2000 03:48 PM

1986 300SDL turbo, 6 cylinder, 126.125, 603.961

My local Mercedes dealer told me it would cost upwards of $1200 dollars to change the timng chain. I don't know if I need a new one or not; I had called to make an appt. to get it checked out--the car is idling slightly roughly.

I can't really afford that much for a fix I don't know I need (the tech said there is no way to check unless you pull the engine part, and once in you might as well do it anyway).

So, my darling boyfriend who maintains the car gets to do this. He has all the service manuals, but I do need to know the exact tools necessary. I found a great site that sells MB tools:, but they use different names than posts here.
So: is a "Locking Nut - Injection Pump Cam Shaft" necessary? Is the "Adaptor bit" the same as a master chain link pressing tool? And what is the tool necessary to get the old chain off?

I appreciate any help.



ncarter 05-16-2000 05:49 PM

$1200 sounds like a ton of money for this job.

I did the timing chain replacement myself over the course of a weekend, including most of the guide rails, plus the all the belts and hoses while I was in there. Granted, that was on a '83 W123 240D, which isn't the same as your car, but I would expect the timing chain replacement procedure to be approximately the same.

The new timing chain will come with an extra link that is not attached to the rest of the chain. You use the crimp tool to attach this extra link to the end of the chain. The crimp tool is like a little vise that presses the link together with the rest of the chain.
That "Adaptor bit" looks like the right thing, although I thought the price was more like $350.00 instead of $35.00. I borrowed one from a local independent shop.

You'll need some way to keep the cam sprocket from turning while you're working on the chain, which *may* be the "Locking nut" deal that you refer to below. Since the sprocket has holes through it, you can just stick something in it to keep it from turning. I used the tire iron, which worked just fine.

To get the old chain off, I don't believe there is a special tool. My service manual just says to "grind open a link of the old chain" - so that's what I did, with a hand-held rotary tool such as a Dremel tool. If/when you do this, make sure you cover up the open engine to keep any bits of ground-off metal from falling down in there. An old bedsheet or a couple pieces of newspaper will work for this.

To put the new chain on, you use the open link that came with the new chain to connect the (opened) old chain and one end of the new chain, then just use a huge socket wrench to crank the engine around to pull the new chain through the engine. Make sure to keep the new chain taut while you're doing this, and make **100% SURE** that you crank the engine in the correct direction. When the new chain is all the way threaded through, you use the chain press tool to connect the two ends of the chain. !voila!

The service manual will have information on changing out the chain slide rails.. I distinctly remember sitting down and figuring out the best order to change out all the rails, chain, and tensioner.. but I don't remember that order any more; it likely wouldn't apply directly to your engine anyway. I also had to take off the radiator, fan shroud, and fan, which makes it extremely easy and convienient to change all the belts and hoses while you're in there.

My total cost for parts was about $250, if I recall correctly, and that included all the sprockets, guide rails, belts, and hoses, plus a few bucks for an icy cold refreshment to keep me going. I got the parts from an OEM supplier, but I'm sure the Parts Shop can hook you up with what you need. Total labor time was about .. uhh, about a weekend.

Now, with all that said, I'm not certain that a rough idle is reason enough to change the timing chain. It's probably worth it to have the chain stretch checked (which should be a minimal expense) to see if you need a new timing chain, before going through the trouble of changing it - or the expense of having it changed.

Good luck.

- Nathan
'83 240D, 250k miles

Harpman 05-17-2000 05:24 AM

My Dearest Rachel,
Imagine you are my wife.........I know, patronize me on this one!
You leaving work (your a nurse, by the way!)and you attempt to start your '86 420SEL/84K in the parking lot, when all of a sudden WHAM !!!!! You call your darling husband whom gave to you and maintains for you (that's me!) your lovely 420 and tell him, "Honey, (that's me!) there was a loud noise when I started the car! I looked under the hood and didn't see anything wrong?" God Bless the innocent! (That's you! - LOL!)
End result...........cheesey, no-nothin' plastic guide rail breaks, lodges between the timing chain and sprocket and takes out two valves! I point out to my gorgeous wife (that's you!) that the hole in the valve cover that's the size of Chicago came from the trashed valves! You laugh, kiss me on the cheek and then sashay off into the sunset!
I, however, am stuck with close to $2200 worth of work! Ahhhhh, the price of love! ROTFLMAO!
Mind you, the total costs did include new injectors and various other mickey mouse items.....since we had to open her up, might as well fix a few others things while we're in there!
The 420SEL's have a history of throwing timing chains, thus the standard recommendation to replace with a double-roller chain!
I was a pleasure role-playing with you! Was it good for you too?
God Bless the boyfriends and husbands of the girlfriends and wives that drive MB's !!!!

akry 05-17-2000 03:16 PM


When the car is running, do you hear any strange noise from the engine?? Such as valve tapping sound or any noise that is not normal??? Usually if the car has some mileage on it, and still on first timing chain, the best bet is have the chain changed whenever possible. You wouldn't want the chain to slip or break when you are cruising at 60mph.....

$1200 might be a bit too much, go around to different dealers, sometimes, different dealer charges different price.... :)

Good luck
Andy Kuo

<LI>1992 Mercedes-Benz 400SE
<LI>Pearl Grey/Black Leather
Mercedes Owners ICQ ActiveList ID#61730549
Mercedes S-Class Page

LarryBible 05-17-2000 06:03 PM


You can't be an idiot, you're smart enough to log onto this great website for information.

I don't recall ever seeing how many miles this car has logged. If it is low mileage with regular and frequent oil changes, you probably have nothing to worry about.

Let us know your mileage and service history on the car.

Good luck,

LarryBible 05-17-2000 06:06 PM


You can't be an idiot, you're smart enough to log onto this great website for information.

I don't recall ever seeing how many miles this car has logged. If it is low mileage with regular and frequent oil changes, you probably have nothing to worry about.

Let us know your mileage and service history on the car.

Good luck,

supergirl 05-17-2000 06:30 PM

It has 250K on it. I bought it a year ago from its one and only owner through a third party. He appears to have kept it in excellent condition. I don't know its repair history, but I cannot imagine that it's on its original chain.

I don't know if it needs to be changed. The Mercedes dealer here (who has been very nice to me in the past) told me that there is no easy way to check this without pulling the radiator and whatnot out. If they are trying to take advantage of me a little bit, hey, it's only to be expected--I'm a short blond girl. No hard feelings. But I'd prefer to have someone else check and save the twelve hundred dollars.

I need to know the exact tools needed to change the chain. And what's all this about putting a double chain on? :confused:

so confused-the most mechanical I get is changing the oil. :D



darius 05-18-2000 11:49 AM

Re: supergirl...your SDL probably has a double-row timing chain, which is something MB vascillates between using (and I wish they had on my 102.985).

On a related note:
Can one of the faithful techs or DIY techs tell me how to check timing chain stretch on my W201.024 (102.985 engine)... OR ... point me to the right section of the shop manuals for this. I have the CD and can't seem to find any reference on how to check the stretch and what is or is not acceptable.

John Meadows
Augusta, GA
'85 190E 2.3

LarryBible 05-18-2000 01:24 PM

The basic procedure for checking the timing chain is to remove the valve cover, and turn the engine CLOCKWISE as you are looking at the engine, standing in front of the car. Turn the crankshaft, which is probably a 27MM bolt carefully until the timing mark lines up on top dead center on the crankshaft balancer. Observe the camshaft timing mark and ensure that it lines up. If the mark is not in sight, turn the engine one more full turn back to top dead center, and the mark should be visible. The mark will be on the camshaft sprocket and will align with another mark on one of the camshaft bearing caps. If while the balancer is aligned at TDC, the camshaft marks lag by more than a degree or maybe two, the chain is stretched and should be replaced.

supergirl, it's possible that on your particular car, you can't get to the crankshaft bolt without removing the radiator, but I will be surprised. Hopefully one of the techs who have dealt with your particular engine/chassis combination can comment on this. I will be surprised if you can't somehow turn the engine without removing the radiator.

Good luck to both of you,

Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

Dingo 05-18-2000 02:42 PM

You're not stupid. Change the chain IMMEDIATELY! Most good techs recommend every 100k. The double row chains rarely break, but the stretch can be enough to allow slack to the point that the engine can literally throw the chain off causing massive damage. In addition, the cain rails are not the most durable in the world and as someone told you earlier they can break off and get wedged in between the chain and the cam sprocket causing disaster ($4000to 6000 worth!). Plus, if the stretch is bad enough it can throw off the timing so that the car will run poorly. $1200 seems very steep. Should be more like $500. I would hesitate to have your boyfriend do the job unless he's done it before. Can be tricky and lethally expensive if not done right!

Good Luck!
Travis the TurboDiesel(1985 300D at 235K) and his owner

darius 05-18-2000 02:46 PM


Many thanks. I shall pull the cover and check. The car has only been mine for the last 4k mi and I can't verify when the last time the stretch was checked. By the way, I have always enjoyed reading your posts here - and I am changing the oil hot and often ;)



85 190E2.3 98kmi

LarryBible 05-19-2000 07:46 AM


supergirl did not buy this car new. For all she knows it had a new timing chain just before she purchased it. It is a relatively small operation to check the chain as long as this engine/chassis combination allows enough room to turn the crankshaft with a wrench. Wouldn't it be better to check it before spending a large amount of money to replace a chain that doesn't need it?

Good luck,

Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

Dingo 05-19-2000 12:18 PM

You're right.:0 I meantto say check the stretch and if it is acceptable(less than 5 degrees I am told) then it's okay. I'd also call 1-800 For Mercedes with the vin number and ask for a recent report on what the MB dealer may have done with it!

Travis the Turbodiesel

Joe-1 05-19-2000 05:51 PM

I had an estimate for the timing chain, tensioner, rail guides and labot for my 1986 190 2.3-16 and it was around $900 dollars for parts and labor. This was thru a M-Benz dealer in New Jersey. Parts came out to about $250 and labor was $650 for dismantling the front cover etc of the 16 valve engine. I hope this might help. Joe

csp475230 05-20-2000 05:47 AM

I have a 1975 230 with 112,000 miles. I purchased it a month ago. Thanks to the post on this site I had my valves adjusted and my timing chain checked. It need to be changed so i had it done also. Total cost 310.00. The car drives great and I now feel much better every time I hit the gas pedal. I went to a independent Mercedes shop. I recommend unless your loaded try and find a good independent guy. Good Luck.

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