This question goes out to all you diesel professionals.

I just performed the 2MM camshaft timing procedure as per the FSM on my 86 300 SDL with 200K. I took three measurements each one consistent; 2MM at 16 degrees ATDC. Spec states 2MM should read 11-12 degrees, if more, replace camshaft or check timing chain elongation. I am assuming the timing chain and camshaft test are the same. The FSM further states that if timing chain is more than 4 degrees then it must be replaced.

Question #1: Is the 4 degrees added to the 12 degrees?
Question #2: If so it looks like I am at the upper limit, should I replace the chain now or wait another 50K.
Question #3: Is there obvious wear patterns or clues to look for regarding the cam?

Inside the engine looks clean, sprockets not worn/damaged, cam is not scored.

I have searched the forums for days and have not found any definitive answers to these questions and would like a few opinions from diesel professionals with more experience than I. Thanks in advance!!

First and foremost, I am not a diesel professional.

I do have a pretty fair engineering background, so take my comments as you wish.

1) If you are confident in your execution of the test outlined by the FSM, then it would appear you are at the limit it describes, i.e., at 2mm your reading should be 11-12 degrees atdc. Instead, you observed 16 deg. so yes, you are at the upper limit.

2) WHy wait? Wait for the chain to stretch enough that a piston hits a valve head? No time like the present.

3) This one MAY be the tricky one. IMO, wear of this magnitude should be visible on the cam. How could the cam account for this?

First, by wear in the cam sprocket, which should be easy enough to observe. Worn teeth will be thinner and possibly have a hooked appearance. If you can compare a known good sprocket, it is usually clear. At 200k, it couldn't hurt to replace it anyway.

Second, the cam could develope a torsional twist, lobes out-of alignment with original indexing. I don't really think this is likely, and have never seen it. But it IS a way that could explain your results.

Third, would be worn lobes. If this were to be the case, there should be clear, easy to see quite highly polished areas on multiple if not all lobes. The original cam faces clearly show they are ground, and have the uniform machine marks that show that. My limited experience with 200k plus mileage 603 cams is limited, but the 2 that I have still appear to be as new.

Hope that helps.

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Chief

1991 350SD