Dear fellow dieselers, I have an ideea in mind to solve the 12deg chain stretch in my fintail (om621). I want to rotate the cam sprocket with one tooth to the right and install the 5 deg woodruff key to the left. That should set the crank timing on +-1 deg.



What do you guys think about it?

No. You want to verify the stretch and change the chain out. To start with if you are reading a 12 degree stretch under no real load. It will be even greater under load. Plus you are not doing any favor to your chain sprockets.

Not that hard to roll a new chain in either or that costly. That is an old tired chain that could fatigue out in theory. Why do overstretched chains fail? With good chain sprockets and chain. The load transfer is well spread across the whole area of sprocket contact. With wear the contact area effectivly is reducing. It can get to the point of increasing the loading to the point the chain can no longer handle it.

Anyways that is a very easy chain to change out. If that chain lets go you will be really sorry.

A rule of thumbs also is as wear increases. It further increases the wear in an exponential fashion. My opinion or the bright side. You caught it before failure.

To echo what Barry said, if you really do have 12 degrees of stretch, REPLACE THE CHAIN. Not only is that chain worn out, but it's going to be eating your sprockets from the rollers no longer lining up properly with the teeth.

__________________
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Hi guys!
I've done it! Only that my valves open 5 deg before the crankshaft reaches 0 deg ( when the cam shaft it's on the notch the crank is at +5 deg). I wonder what's worse 5 earlier or 5 deg later.
If the chain stretches further under load then I should be fine.

I want to play a bit, the engine is worn out any way. I've got 19, 16,16,14 bar at the compression test, so much life it's not left in it anyway.

Best to borrow a dial gauge if you do not own one and check. There is a procedure recommended. Using the crank and cam marks is not considered a true test. Has a lot of relativity at the same time though.

They were only intended to aid in putting the engine together at the plant. Or if you really feel the engine is on it's last legs and do not care. As one hamburger joint slogan goes. Have it your way.

At my age you have and had things around that are on their last legs. As well as yourself. That adds another factor to my mix. Who or what goes first.