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Old 10-26-2005, 01:25 PM
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Join Date: Sep 2005
Location: Austin, TX
Posts: 41
300sd Timing chain replacement question.

I am needing to replace the timing chain on an 83 300sd (250+k). There appears to be 5-8degrees stretch. On this site's DIY chain replacement link, it does not say to change the chain's tensor. Dieselgiant's link say YES YES YES change the tensor (which adds a lot of extra work).

Any thoughts on this? Is there pros and cons to replacing or not?


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Old 10-26-2005, 01:43 PM
Join Date: May 2002
Location: Blue Point, NY
Posts: 25,396
The "tensioner" is mounted to the side of the head and is easily removed with a couple of screws. I recently had the tensioner out of the SD to replace the head. It looked in perfectly functional condition. I purchased a new spring and reinstalled it.

I'm failing to grasp why the tensioner should be replaced on principle.
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Old 10-26-2005, 01:49 PM
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Join Date: Sep 2004
Posts: 9,087
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I too would have done only the spring. Perhaps you heard to replace those guide rails?

Also, have you tried to correct the stretch with some of those Woodruff keys available?
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.

Liberty will not descend to a people; a people must raise themselves to liberty.
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Old 10-26-2005, 04:48 PM
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Join Date: Sep 2005
Location: Austin, TX
Posts: 41

Thanks for the info....I will buy a new spring for it and when I replace the chain I will check the tensor's condition, but definately replace the spring.
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Old 10-26-2005, 06:18 PM
Old Deis
Posts: n/a
The tensioner itself is a ratcheting device. You should remove it and first check the spring. It usually shows wear, it gets worn along the sides, or it is just plain weak. Then the ram in the center should be cleaned and reinserted from the backside. It should hold when yor try to push it backwards through. I noted on a new one that it did not hold when shoved hard. But it should hold to moderate shoving. If not, replace the assembly.
The banana slide should be replaced as a matter of course in my humble opinion, it is easy and cheap to do. With 250k on the clock it will be worn and just do it. That slide has wrecked a few engines when it came apart. Gets brittle with age. Will stop a potential catastrphic event from happening if you get to it now.

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