Help reading my timing chain stretch (pic included) - Page 2 - PeachParts Mercedes-Benz Forum

Rick Miley · #16 07-01-2010, 01:01 PM

Quote:

Originally Posted by leathermang

Rick... why did you not add the link to that thread I always have to email you to ask for... which has that ' add or subtract X degrees factor' in this procedure ?

I added it to my signature so you'll never lose it again.

Of course if I take another year or so off from posting you might have some trouble finding a post. But they are out there.

leathermang · #17 07-01-2010, 01:41 PM

Thank you. I have it saved in my documents somewhere... but it was always easier to ask you...
Some may not know you are a compulsive information saver/organizer.... but your skills need to be checked once in a while... that is the excuse I tell myself when I email you to find it...
Well , lets just stick the actual posts here by Steve Brotherton, former moderator here and also the definitive info on setting the auto trans vacuum modulator:
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I have looked at hundreds of MB timing marks (at the cam) and they are only accurate enough to know which tooth to line up. There is 18degrees between each tooth. If you marked and followed your own specific motor you might could form a judgement. To just drop in and view it isn't good science.

The proper way to do it is very simple. The valve clearance is removed and the engine rotated till the intake valve on number one cylinder is pushed exactly 2mm down by the cam lobe. Any resonable dial indicator will measure this.

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When the motor is in this position the crank position is read from the crank scale and indicator and compared to the book value. In the case af a 617.95 motor with cam ID 11 it should say 11deg ATDC. If it says 21deg then there would be ten degrees of stretch and a new chain would be in order.

I threw that 10deg increment out because I consider that much to be obvious, it might take 350,000 miles to stretch one that much though and if asked I say replace it at 200k. I very seldom measure chains by anything more than mileage and noise. I would replace anything in doubt over 100k. (ALL mileage numbers are my opinion only!!) (The timing numbers for cam ID 11 came from 1985 TDM)
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The tentioner check valve should hold tention between running periods, but often does't. I would replace any tentioner with over 100k mi that exhibited such slop. (matybe anyone period)

I would never do a cam timing correction based upon your judgement of the line-up of the marks. I have never seen a motor where the marks lined up exactly, after all they are there to allow you to judge the set-up to within one tooth (18 degrees).

If you were changing offset keys then you would push back the chain tentioner with a prybar/screwdriver to make the chain slack. Then take the nut off and gently tap the gear off the shaft. After changing gear, key, or whatever pick the gear and chain back up pulling tight on the drivers side and slide the gear back over the cam turning the cam to line up the key with the gear. You should do this of course with the crank gear on TDC and the cam in the #1 position.

I would recommend that anyone doing this for the first time pull the rocker stands and arms off, so that the motor can be turned afterward and the timing verified without the possibility of hitting valves.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician