need help understanding timing chain stretch
 

I've read the DIY Article, and after I did the Quick method (aligning the tower/cam gear) I'm at 5degrees(+ or - a degree) so that should mean I need a 6 degree keyway right? to get my alignment to 11 degrees ATDC. SO once the woodruff key is in and I align the tower marks again I should read 11 degree on the crank pully....Right?? not 0

Cam chain stretch is always measured as CRANK degrees.
So if you have 9 degrees of retard then the cam is actually 4 and 1/2 degrees retarded...exactly half that of the crank.

With a retard of 5 degrees, you need a 4 degree woodruff key to be within 1 degree of 0.

Why are you talking about 11 degrees ATDC ?

The pump timing is 15 atdc on the 6 cylinder MB diesel and 24 btdc on 240's and 300's.



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He is talking about using the 2mm valve travel method.

Oh :rolleyes:

Silly me:D


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You've got the two methods confused.

The quick method, using the tower marks, should have the reading at 0 degrees on the crankshaft damper when the marks are perfectly aligned. This is not easy to do.......the mark must be right in the middle of the notch.........if you pass it slightly, you cannot reverse it and get the proper reading.........you must go around twice and try it again.

The "proper" method, using the two millimeter valve lift, uses the specification of 11 degrees ATDC with a used chain on the crank pulley.

Presumably, if you're 5 degrees late with the quick method, the "proper" method will read 16 ATDC on the crank pulley. However, rarely do the two methods agree exactly. The proper method is more accurate.

There are Woodruff keys available for crankshaft readings of 4, 6.5, 8, and 10 degrees ATDC.

Thanks. for clearing that up!
So if I'm out 5 degrees, do I go with the 4 or 6 degree key? how many degrees does it take to effect cold weather starting and power?
BTW I called the local dealer for a Key and there is none in stock! in the city, but it can be ordered from Germany and will take at least a week, they were 10$ (I think I'll order a 4 and 6)

No. You need the 2degree offset key.

http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=1Y501QRV21Y501R0F7&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1983&product=A4190-21384&application=000041566

Sorry to hijack the thread a little, but if when using the quick 'align camshaft' method, I get 11 degrees at the crank, I assume I'm looking at time to replace the chain?

Thanks for any info.

If you are sure (check it at least two or three times) then yes, ASAP.

Some things can not be done ' Quick" and RIGHT at the same time...

Just take Brian's word on this if you want quick AND Right...

but if you can't do that...

Then check the archives where Steve Brotherton explains why the cam method is not proper at this time in your engine's life...

That method is only for checking ( read ball park ) when building a new engine...

The hidden reasons which the Mercedes Engineers prescribed the 2 mm valve movement method include the fact that there are wear surfaces inside your engine which may or may not either multiply the effect of something else..or offset it... one generic example is chain pin and link wear... which may be offset in its NET effect by wear on the sprocket it runs on...

OR... lets say an offset woodruff has already been installed... then what you order would be thrown off since they are calculated from a different ' base'...

Mercedes specified a Performance Criteria ( the 2mm valve lift ) for a reason...

Lance, I cannot figure out why the suppliers confuse folks with references to the camshaft. The FSM references the keys based upon crankshaft position.

The four degree key is .7mm offset and has M/B p/n 621 991 04 67

Why confuse things and bring the camshaft into the discussion?

Either key will be fine. The engine is quite tolerant of camshaft timing that is off by two or three degrees.

Don't attempt this change of Woodruff key unless you know precisely what you're doing. Carefully search the archives for the procedure. It's fraught with risk of dropping the chain off the crankshaft and losing the engine timing completely. It's also fraught with risk of dropping hardware (thrust washer or woodruff key) down the chain gallery where it's almost impossible to retrieve.

The cost of a mistake on this procedure is very high. A word to the wise.

Me either... the only correct accurate method for your used engine is the one Brian referenced.

That may look like a very serious bold statement... but it is actually an understatement....Print it out and tape it to your hand....

While correcting the chain elongation with woodruff keys is perfectly correct... I really believe most people are better off to replace the chain... AND all that contacts it.. rails,tensioners ETC.... in the long run those are the items most likely to trash your engine without warning. Greg

Why? He says he has 5* elongation as marked on his crankshaft balancer. What ever he changes on the camshaft position will be double on the crank. Installing the 2* offset key will take off 4* at the crank, bringing him to 1* off.

It's a simple concept that people turn crybaby about because they have to *think* about what they need. At least Fastlane gives the correct explanation: " Note: 2 Degrees
Offset Woodruff Key 0.7mm = 4 deg. at crank"