Actually if you have a long enough extension you can do as you said and hoop up a dial indicator to get TDC if you want to check the pointer.

I think it was Army/Stretch that mentioned you can bring the Piston up close to TDC and remove the upper Valve Spring Retainer and let the vlave go down and contact the piston. Arrange the dial indicator so that the extension is on the top of the valve stem and slowly and carefully continue the rotation in the proper direction till TDC. Then look down and see if what is lined up with the pointer.

Concerning the match marks on the cam Tower and the back of the timing gear. The angle that you are viewing them at can throw off your reading.

Concerning Engine Match Marks in general they are used all over the world on any manner of Engines and have proved sufficient for practical purposes. And these Engines have been around long enough for some issue to have previously shown up and be known concerning the Engine Match Marks.

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84 300D, 82 Volvo 244Gl Diesel

[QUOTE=Shern;4127843]I think a lot of the trepidation over when to replace a timing chain is due to some makes of Cars needed the Timing Chains replaced after say 150 thousand miles changed due to the Nylon gear teeth on the larger gear and the use of no timing chain tensioner (when I replaced that on my Chevy 4.3 liter engine both replacment gears had steel teeth).
Next would be the Mechanics either uneducated in Mercedes 617.952s or looking for work to scare you and trying to sell you a timing chain replacement job.

It seems pretty well know now that on the 617.952s it is the Timer Bushing that is the most frequent cause of the Vacuum Pump failures that snap timing chains and damage engines. Next in line would be some issue with the Vacuum Pump.

The other thing but not specific to the timing chain is if that little snap ring on the Oil Pump Chain tensioner wears out and the tensioner shoe move around and caused binding on the Chain. Or if the spring broke.

I guess next would be an issue with the The Timing Chain Tensioner rail or the tensioner.

Notice that the above has nothing to do with the IWIS/jWIS timing chain itself.

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84 300D, 82 Volvo 244Gl Diesel

911 to the rescue, eh?
Thank you for that. I’ve always felt the cam/dial issue was a little over blown.
Reminds me a bit of speeding ticket litigation in the 90s. The argument being the position of driver’s head caused misread of speedo dial. I’d love to see a comparison of the dial gauge method versus cam/balancer marks.

The timer bushing issue pertains to the 616 as well I’m assuming?

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1981 240D 4sp manual. Ivory White.

Having timed at least 200 sets of camshafts for maximum power on a dyno there are a few observations:

1. 3 degrees is not going to be noticed with a conventional street cam in a diesel. You would need a very high performance cam for it to make more than a 2% difference
2. The dial indicator method is not all that accurate. You can easily be off 2-3 degrees when comparing to hard stop index methods used by race teams and OEM production.

The decision is always up to the owner, but don't expect much.