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Old 01-21-2003, 10:49 AM
Thomaspin's Avatar
Join Date: Jun 2001
Location: CA
Posts: 531
Changing the 8 cylinder timing chain - illustrated

I did this job over the weekend on my wife's 1981 380SLC - a 116.960 engine, converted to a dual row timing chain many years ago.

The job will be similar for the 116 5 litre and 117 4.2 and 5.6 litre engines.

Note that if you remove the distributor (to replace chain rails) on the early 3.8 litre engines, it has to be re-timed with an ignition light as timing is not electronic on the earlier cars. I will add illustrations on this soon.

An illustrated version appears on my web site. The related change of rails (this was on my 1990 560SEL - again, the job on the 3.8 litre is very similar, though the 107 chassis affords far less working space) appears here.

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Old 01-21-2003, 02:01 PM
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Join Date: Dec 2002
Location: New Jersey
Posts: 218
Great info

Thank you for taking the time to walk us through the process of changing the timing chain. I have a 1983 300SD and to my knowledge have never done this. It has 260,000 miles on it and i have owned it for the last 50,000+. The person before me owned it for at least 100,000 miles and never changed the chain. The car runs great, starts up great in cold weather and i get about 30mpg. I have no problems with it. How will I know if my chain needs replacement and is the same procedure used on a deisel?
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Old 01-21-2003, 02:31 PM
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Join Date: Jun 2001
Location: CA
Posts: 531

Thanks for the nice comments.

On your 5 cylinder turbodiesel, you should remove the cam cover and the fan. Then, rotate the engine using a socket on the crankshaft until the timing marks on the cam and cam tower align (similar to what my pictures show for the V8). Then take a look at the degree wheel on the cranshaft and see how many degrees past zero it is. (If you have difficulty getting at the fourth fan retaining bolt, turn the fan with a 22mm socket on the nut on the power steering pump. You have to loosen all four and remove three to get the fan out).

On my 300SD (1983) I replaced the chain at 7 degrees of indicated 'stretch' at a very young 100k miles.. Now, older and wiser, I would first replace the chain tensioner and see what the indicated stretch is then. My SD has a stepped tensioner (unlike the sprung piston in the V8s). Replacement is easy. If, after replacement, the chain still shows over 7-8 degrees of stretch, I would change it.

If your guides/tensioner/chain are very worn, you will hear the chain rattle against the engine casing when first started. On the V8s, failure usually results from a guide getting slapped and broken by the chain, riding up between the chain and the cam gear and forcing the chain to skip a tooth, with expensive damage to the top end. Some suggest diesels are also prone to camshaft fracture - maybe caused by the higher compression.

The in-line 5 has one big advantage in this regard over the V8 - a shorter chain with a simple loop path, rather than the tortuous direction reversing path in the V8, so it tends to wear chain guides less. At your mileage, I would consider changing the upper guides as well - they are cheap.

The process is similar to that for the V8 engines.

I did crimp the chain on the I5 as the tool could be rented in those days. Now, as I do not want to spend the $300+ on a rarely used tool, I would seek to borrow it or would use a clip.
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Old 01-21-2003, 03:47 PM
Join Date: Dec 2001
Location: Southern California, U.S.A.
Posts: 8,508
Again you've done an excellent job!

I think you may have missed your real talent. You could be a Mercedes mechanic.

Or better yet, create DIY guides with written instructions and illustrations for other jobs, such as water pump replacement, alternator replacement, oil changes, simple tune-ups, etc. You could also sell them in pamphlet or book form.
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".
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Old 01-30-2003, 11:58 PM
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Join Date: Feb 2002
Location: Virginia
Posts: 550
Thumbs up

I just want to echo the comments here. Obviously you took even longer than necessary to do a long hard job so that you could document it so thoroughly - not to mention a couple additional hours of prep so that you could post these to the web. Your efforts also have been appreciated over on the SL email list at Who knows how many 116/117 engines you've saved from an early death???? THANK YOU.

(Now if I could just work up the gumption to actually do mine....)

82 300 SD
77 450 SL (gone)
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Old 01-31-2003, 01:13 AM
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Join Date: Aug 1999
Location: ajax, ontario, canada
Posts: 773
even though I don't own a V8 benz (yet), I have to say that these are very thoughtfully documented illustrations. I'm sure many people will benefit from these.

And the humour is also well appreciated ...
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Old 01-31-2003, 10:09 PM
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Join Date: Dec 2002
Location: Colleyville, Texas
Posts: 2,694
Thank You for your time and effort.
I have a few cars and have not replaced a timming chain yet but I know it will be comming.

I do have a technical question. On the 560 rail change that you show on your web site the end results were different than on the 380 SL timing chain replacement.
Because of the larger displacement does the 560 require gin and vermouth at the completion of the job vs. the 380?????????

Additionally I'm not a gin and vermouth man, will bourbon do???

1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car
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Old 02-01-2003, 11:15 AM
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Join Date: Jun 2001
Location: CA
Posts: 531

I did not change the chain on the 560 engine, just the rails and tensioner, as the 560 was only stretched 5 degrees at conclusion.

In contrast, after changing the 380 rails and tensioner, the chain remained stretched over 8 degrees, so I changed the chain also, for net 0 degree stretch.

I will change the 560 chain at 8 degrees - approx. 160k miles in my case. YMMV.

Last edited by Thomaspin; 02-02-2003 at 12:22 PM.
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Old 02-17-2003, 02:21 PM
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Join Date: Jun 2001
Posts: 259
Thanks for your detailed explanation -then a question.

I really appreciate the pics of your timing chain surgery. It gave me the stones to open mine up to check for slack. Some weekend when I have more time, I'll do the rails and the tensioner on mine.

I did have a question about the stretch reading:

With the valve cover off, and the hash marks lined up on TDC, my damper reads right at 0 degress maybe 1/2. However when I totally relaxed the breaker bar and 27mmsocket, (actually it might have backed up a bit it slacked back to 8 or 10 degrees. Too much play to just ignore. Would you supose a correct reading would have the chain tight or should the slackened reading be the telling one?


J. Boggs
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Old 02-18-2003, 10:20 AM
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Join Date: Jun 2001
Location: CA
Posts: 531
J Boggs

Sounds like something else is loose in your drivertrain I get the same 0-0 reading wheher there is tension on the chain or not, after 2 360 degree rotations to charge up the tensioner. Is your tensioner new?
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Old 02-18-2003, 12:06 PM
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Join Date: Jan 2003
Location: St. George, UT
Posts: 11

I appreciate your efforts as I am going to do replace my rails and chain ('84 380SE) this weekend as "might as well's" in conjuction with a camshaft replacement. I have studied both of your guides and feel ready to do it. I also have the service CDs, but their photos leave a lot to be desired.

One concern I have, however, is how difficult is it to hold the new chain rails in place as the new pins are driven in? There doesn't seen to be a lot of room for a hand and I shudder to think about dropping one down behind the timing cover. Or is it easier than it looks? Also, I am replacing the tensioner rail and tensioner just for good measure. Does the '84 380 have the electronic distributor timing control?

Thanks again,
Even a broken clock is right twice a day.

'84 380SE
'66 MGB Roadster
'85 Mazda RX7
'91 Chevy P/U
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Old 02-18-2003, 12:24 PM
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Join Date: Jun 2001
Location: CA
Posts: 531

On the tensioner rail, try the technique (on my site) of placing a long screwdriver through the part-inserted lower (and only) pivot pin to stop the tensioner rail falling through. Insert the rail until you feeel the screwdriver, then remove the screwdriver, drop (!) the rail a little lower and push in the pivot pin.

On the others, yes, it is easy to drop them. I used clean gloves to hold the top of the rail (no grease, better grip than naked hands). Really not that risky but you have to concentrate hard and have absolutely no distractions.

An alternative is to use a pair of fine nosed locking pliers, but I feel less comfortable with this approach.

Finally, if you focus on inserting the lower pins in the three flat rails first, the upper pin female fitting on the rail is a natural place to run a piece of wire or string through to be absolutely sure you do have something to grab if you drop the rail - that would be the safest way.

Can't swear to it, but I believe '84 and on had the full electronic timing.
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Old 02-18-2003, 01:01 PM
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Join Date: Jan 2003
Posts: 258
first of all, thank you for the nice write-up. It has given me a lot of motivation in doing my chain ( 91 560 SEL 145,000 miles with original chain rails ...i was told). I have some questions for my clarification.

1. You mentioned i needed (6) pivot pins ( page 15), however you showed (2) for the RHS flat side rails ( page 17), (1) for the tensioner rail ( page 20), and (4) on the drivers side (page 33) - which make it a total of 7. can you clarify?

2. Removing the pins appear to be a difficult task. I find it difficult to imagine how your home made pin puller works (page 22). It looks like the pins have female threads on them ( page 23). do you pull them out ( straight out), or do you need a turning motion while pulling them out?

3. Do I replace the guides and rails first before replacing the chain? or does it matter?
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Old 02-18-2003, 01:13 PM
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Join Date: Jun 2001
Posts: 259
Chain Tensioner...

As for my chain slack, no I haven't changed out the tensioner-but will right away. What was that about two revolutions to load it?
Does that have to be done by hand? Damn, I already put the fan back on!

Thanks. Great thread.

J. Boggs
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Old 02-18-2003, 01:54 PM
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Join Date: Jun 2001
Location: CA
Posts: 531
The two revs help charge up the tensioner with oil

I don't know that you have to do it but it does help remove any slack in the chain and reduces stress on the guides.

If you don't want to bother with removing the fan again, crank the engine with the starter only - pull the feed from the ignition coil to the distributor before turning the starter key.

The tough thing about removing the fan is getting the four bolts accessible - you can make it much easier by simply using the power steering pump bolts (22mm) to turn the fan, bringing each bolt uppermost in turn.

I would remove the fan. 1 hour, no heartache.

Note my approach to installing the new tensioner - it's very tough to do using strength alone.
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