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Old 01-27-2015, 03:42 PM
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Join Date: Jan 2008
Posts: 99
Timing Chain Stretch and Tensioner?

Chain post

I've started getting a repetitive clicking sound the engine of my 380sl , particularly when the engine is cold, and I haven't been able find out where it was coming from with a stethoscope. So, I decided to check the timing chain stretch by rotating the engine until the mark on the passenger side (right) cam lined up with the mark on that cam tower, and the mark on the driver's side cam to lined up a hair-off with the mark on that cam tower, as I believe it's supposed to.

However, I was surprised to find that the harmonic balancer was at app. 10 degrees when, IIRC, it should have been at zero, especially because I replaced the double chain less than 100k miles ago, and I change the oil every 3K miles

So, before I change the chain again, I was wondering if:

(1) My having removed the tensioner before I rotated the engine and checked the stretch could have had anything to do with the chain being 10 degrees off,
(2) It's possible that the IWIS chain I used somehow stretched more than an OE chain would have; and if
(3) Anybody here has ever used a chain made by SWS.
Thanks very much in advance for the quick responses, since my car will be sitting in my garage until I am confident that I can fix it properly.

1981 380sl
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Old 01-28-2015, 12:11 AM
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Join Date: Nov 2002
Posts: 766
chain stretch can't be accurate if the tensioner is missing. reinstall it and try again. good luck, chuck.
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Old 01-28-2015, 12:14 AM
w123fanman's Avatar
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Location: Georgia Tech, Atlanta, GA
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From what I have heard the IWIS chain is what you will get from the dealer, just with the dealer mark up.
Current: 80 300SD OM606 project, 83 300D 5-speed project, 88 Yugo GVX, 90 300D OM603 swap, 90 Lexus LS400, 91 F150 4.6 4v swap, 93 190E Sportline LE 3.0L swap, 93 190E Sportline LE Megasquirt, 03 Sprinter
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Old 01-28-2015, 12:43 AM
Hit Man X's Avatar
Join Date: Sep 2004
Posts: 9,087
Thumbs up

I have never checked chain stretch with the tensioner out.

IWIS is top notch stuff, I have used them with great success in all of my vehicles. Even with a new chain and new rails in the 560, the cams were still about -1į late... tossed in some +2į woodruff keys. Now they are +1į, I figure the chain will elongate and I will be fine.
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.

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Old 01-28-2015, 09:47 AM
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Join Date: Jan 2008
Posts: 99
Thanks very much for the fast and informative replies. I Ďve posted pictures of the right and left cam shaft marks and their tower marks, as well as a picture of the harmonic balancer mark, showing that it is approximately 10 degrees off.

Originally Posted by porkface View Post
chain stretch can't be accurate if the tensioner is missing. reinstall it and try again. good luck, chuck.
As it turns out, I thought I had removed the tensioner. But I only loosened the bolts slightly to see how difficult removing them would be. So, the tensioner is still putting its regular pressure on the chain.

At this point Iím assuming that the prudent thing to do would be to change the timing chain, but Iím still wondering whether I need to change the tensioner and its rail, considering that I change them when I changed the chain less that 100K miles ago, and AFAIK the tensioner rail doesnít break? OTOH, since I replaced the two plastic, top rails, which Iíve heard are most prone to breaking, with metal rails at that time, Iím assuming that theyíre still good.

Since Iíve already removed everything that needs to be removed to replace the chain, Iíd hate to have to put everything back together to drive it to an Indy for him to replace it, and Iíd also hate to have it towed there. But Iím afraid to replace the chain myself, considering the problems that screwing the job up can create. So, I was wondering if thatís something I can do alone, considering that Iíve done a lot of other stuff before.

Any additional help would also be greatly appreciated.
Attached Thumbnails
Timing Chain Stretch and Tensioner?-right-cam.jpg   Timing Chain Stretch and Tensioner?-left-cam.jpg   Timing Chain Stretch and Tensioner?-crank-shaft.jpg  
1981 380sl
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Old 01-28-2015, 10:19 PM
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Join Date: Nov 2002
Posts: 766
life expectancy is aprox 100k on any chain, including oe mercedes. replace the chain, tens and rails-all 4. i replace them anywhere after 7 when i see them. 10 means it may jump a tooth or 2. good luck, chuck.
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Old 01-28-2015, 11:39 PM
franklyspeaking's Avatar
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Join Date: Dec 2001
Location: Decatur, Alabama
Posts: 383
I think the chain tensioner would have no impact on chain stretch measurement. The chain is tight on the pulling side. The tensioner just takes up slack on the backside. I had a tensioner fail on a 240D - ran fine until the chain double wrapped around the crank sprocket and broke.

1998 C280
1982 240D Manual - Sold
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