Unfortunately the tentioner in these 116/117 motors is not a ratcheting one. I replace a tentioner when it regularly looses its pressure overnight. This is noticed by a rattling sound on start-up that goes away after oil pressure fixes the tentioner. This rattling is what does in the upper rails when they are brittle. It will happen occasionally no matter how good the tentioner. If I heard it twice in a hundred starts I would probably replace the tentioner. Maybe twice in 50. if the rattle didn't cease instantly with oil pressure on the gauge I would also replace it.

The point of doing nothing is that since you will need a valve job when it comes apart anyway the only difference that letting it fail will bring is the need for four exhaust valves, maybe a couple intake but not often. All the labor will be the same and 80% of the parts which is the small part of the job.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Steve - not to hijack Damon's thread, but I'm about to do the upper guides on my 560SL. It has 40,000 miles on it and I am assuming everything is original. I have a new tensioner on hand that someone gave me and was debating on whether to change it now or not. No issues noticed with rattling on start up. Just because I happen to have one on hand, should I go ahead and change it or save it for the next time?

Thanks.

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Len
'59 220S Cabriolet-SOLD and living happily in Malta
'83 240D 351,500 miles original owner-SOLD
'88 560SL 41,000 miles - totaled and parted out
https://sites.google.com/site/mercedesstuff/home
'99 E300 turbo 227,500 miles
'03 SLK320 40,000 miles - gave to my daughter
'14 Smart electric coupe 28,500 miles
'14 Smart electric cabriolet 28,500 miles
'15 Smart electric coupe 28,000 miles

If I had one, and it was Genuine I'd go ahead and replace it just for good measure.

Otherwise I'd consider just freshening the seal on a unit w/ only 40K.

Jonathan

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Blue Ridge Mercedes
Jonathan Hodgman
http://www.blueridgemb.com/
Enthusiast Service, Restoration & Tuning.
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Specializing in all pre and post merger AMG's including Hammers and DOHC M117 engines.
Mercedes Repair Atlanta

I see no technical reason to change it now. The part is very durable. I believe the only problem that ever occurs with the tentioner is contamination from debris in the oil. The act of loosing pressure over time is a matter of the check valve not holding and I have always thought this was due to oil grit in the check ball. As a result of this concept mileage is not really an issue. The issue is performance.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician