*Chain stretch via dial indicator
 

Who’s used this technique on an om61x?

I’m at 215k.
Via crank method it’s always shown 2 degrees.
Last I checked, it was 3.5.
Thinking it might be woodruff time.




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Others with more skills and experience than I are the ones to listen to, but I would not change my camshaft and injection pump timing without doing the test as recommended by the factory manual. It's not that hard. Then, having accurate numbers, one can judge whether a new woodruff, a new chain, or nothing at all. Seat of the pants stuff makes me nervous.

This is from my notes. Note I have never done it so re-check on the notes.

5 Degrees Offset Woodruff Key 1.3mm = 10 deg. at crank Offset woodruff key for correction of cam timing.
3 Degrees Offset Woodruff Key 0.9mm = 6.5deg. at crank
2 Degrees Offset Woodruff Key 0.7mm = 4 deg. at crank

It won't make any noticeable running difference with so little stretch

Yeah but that’s off the crank. From what I understand my reading could be off by as many as 5 degrees. This is why I’m curious about checking chain stretch via dial method.

Exactly. The dial method is the method recommended via FSM, ergo my query.

I have, a few times on at least two OM616s. It is the best way to know cam timing accurately. You need a dial indicator that is scaled right for the measurement, and a way to hold it in place.

I used a magnetic base with jointed arm for holding the dial indicator in place. I bought a set of extensions for the rod to keep the tool above the rocker and cam, which provided a straight shot down to the valve spring retainer. It helps to use a longer tool for rotating the engine, so you have greater control and are less likely to overshoot the 2mm depth.

Here's what I'm looking for.

Did you end up using any woodruff keys to correct?

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I did, in the '74's engine. I installed a 0.7mm offset key as mentioned above in post #3. That restored cam timing to spec but I didn't pick up any noticeable power, that's for sure!

While using a dial indicator to measure the movement of a valve provides an admirable degree of accuracy, the reliance upon the production marks from the factory to determine the position of the crankshaft tends to negate the usefulness of the indicator's accuracy.

Who is to say that the pointer is correctly located in the front of the chain case? Who is to say that the circumference of the balance disc or torsional dampner is correctly marked for TDC or the number of degrees before or after? If TDC has not been verified for all of the specific components (crankshaft, balance disc/dampner, pointer) then only one part of the reference, the valve lift, is accurately known. Crankshaft position is not accurately known.

Ah, a post-structuralist... ;)

Have you encountered many om61xs with factory defective crank pointers?

Do you have a better method?

Oh, Poopy Poop!

As for the accuracy of the scale, I trust German engineering and manufacturing skills. Plus, on these engines those whacky Germans provided a way to adjust the pointer to match actual, for real TDC:

- Pull #1 injector and pre-chamber;
- Insert wood dowel rod into the hole 'til it rests on the top of the piston;
- Rotate engine at crank on compression stroke for #1 until the dowel indicates true TDC for #1;
- Check the pointer on the front of the engine for accuracy against the scale. If found to be inaccurate loosen its retaining bolt and adjust the pointer to indicate TDC; and
- Problem(s) solved.

:D

Was Socrates a post-structuralist?

See below.

The concept of the above described process is both correct and necessary. For the dowel substitute a dial indicator, note the crank position with the piston ~.100-.125" both before and after the presumed TDC, and split the difference. There will be a dead area of piston movement + 2.5-3 degrees at TDC where dowel movement will not be detected, hence the need for bracketing the piston position via the indicator.

Even better! Use the dial indicator with rod extensions inserted through the pre-chamber hole to establish TDC. That's a great idea and more sure than observing movement of the dowel rod. I gladly update my process as outlined above to include the use of dial indicator instead of a dowel rod.

I'm sure the factory guys got the pointer set right to begin with. Could it have been moved from the correct position at some point in time? Yes, it is possible. You raise a valid point, Frank. If in doubt check and re-align if needed.

[QUOTE=Frank Reiner;4127807]Was Socrates a post-structuralist?

The Socratic response would have included both point and counterpoint.
Looks like we got there in the end.

Thank you gents, I appreciate the techniques.
Lately I’ve seen more discussions on rolling a new chain, than those using offset keys. Could be a function of age or just a dying art. I have been curious all the same.

Thanks again