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Old 02-05-2005, 12:24 PM
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Location: Nashua, NH
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Timing Chain Questions: Slack/Tensioner

I was replacing the cam oiler tube clips on my 1988 560SL and when I took the driver's side valve cover off I could see there was a lot of slack in the timing chain. I could lift the inboard side about 1/2" away from the guide. The chain was resting on the guide, in full contact with it when I opened it up.

Also, the chain guides were dark reddish brown so it looks like I have to first replace the chain tensioner and then have the guides done. Does that sound like a good way to procede? I don't think I want to tackle the guides myself but do you think it is OK to replace the tensioner and then I could drive it to a shop to have the guides done? I've attached some photos to see it, in the first is the chain as it looked when I removed the cover, but the second shows my finger lifting the chain off the guide.

One question here, does the gasket on the tensioner require sealant when a new one is installed??

The engine doesn't seem too noisy to me at idle, so maybe the tensioner is just draining down after sitting a while but still it didn't seem "normal" to have that much slack in the I right??

On the bright side the valve train looked nice and clean with no noticeable sludge (even the top of the valve cover was pretty clean) and there was no visible wear on the lobes so the oiler must have been OK all these years.

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Timing Chain Questions: Slack/Tensioner-chain-0001.jpg   Timing Chain Questions: Slack/Tensioner-chain-0002.jpg  
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Old 02-05-2005, 02:43 PM
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What's the milage on your 560? If the tensioner is fully extended and you still have slack in the chain that means your chain is streched and you may need a new chain? I don't really know how much strech is too much strech. Maybe your tensioner is still good and you only need new chain, or maybe you only need a new tensioner if yours isn't working properly to tighten the chain? I am not an expert so I am just trying to throw out some ideas.

I also checked the chain on my 560 last week and the strech on mine is worse than yours. Mine is about 3/4" to 1" from the guide to the chain . This is the original chain with 290K miles on it so I am going to have the chain and tensioner replaced VERY soon. The top guides look ok (clear brown but not dark brown) so I am not going to replace them ($$$ is tight right now). I figure I don't really need new guides because the new tensioner & chain are going to be tight and the chain won't be rubbing agaisnt the top guides too much to brake them. Right now the car is on "vacation" until I replace the chain & tensioner.

To replace the guides you need to have a special puller. Be careful not to break the guides in the process or drop anything in there and you will have to take the chain cover off (not good).. i think it's better to have the shop does it if you don't have the tool.

I contacted a reputable indy MB shop and was quoted $212 (labor only) to replace/roll in new chain. I did not ask how much to replace the three top guides. To replace the other three guides the chain cover has to come off.

You don't need sealant when installing new tensioner assuming you are also replacing with it new tensioner gasket. That's what the gasket is for.
1991 420SEL Project Car (Completed and rides beautifully)
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89 560SL
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Old 02-05-2005, 05:05 PM
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Thanks for the reply. My car only has 109K on it so it would seem unlikely that the chain is stretched beyond the limits of the tensioner, but I've ordered a replacement tensioner and will install it next week to see for sure!

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Old 02-05-2005, 06:03 PM
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Decision Time- Replace Timing Chain?

560SL Timing Chain Replace

Changing the 8 cylinder timing chain - illustrated

These are worth reading. Thomaspin's site is well worth the $30 IMHO.

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1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)
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