OM60x timing chain check=2.5* advanced?

[bhowell]

OM60x timing chain check=2.5* advanced?
89 190d timing chain check=2.5* advanced?

Checked the timing chain stretch while doing 5 new rubber intake boots, 4 new air cleaner box side bushings, some new PVC bits, and 5 new glow plugs. Used the opportunity to remove the valve cover, and check the timing chain stretch & injection timing. Weird measurement result.

The factory timing marks molded into the rubber on the balance were deteriorated on the ATDC side, but easyto read on the BTDC side. An extremely precise set of new markings were made using Microsoft Publisher, and some paper/tape. You can see from the picture how precise the new markings are. They may look slightly off from an angle, but looking strait down after rotating through each significant mark of 40BTDC, 30BTDC, 20BTDC, 10BTDC, 0BTDC, ect; revealed perfect alignment.

The weird result was that with the camshaft timing marks perfectly aligned; the crankshaft markings indicate the timing is 2.5 degrees BTDC. Even if you discredit the homemade timing marks on the paper/tape, you can still clearly see that it is coming up ahead of the " O'T " mark for the Zero degrees separation mark:
(<- ATDC <- O'T -> BTDC ->.


I cranked it up for a few seconds to re-pressurize the timing chain tensioner with oil. This resulted in the exact same measurement afterwards.

The odometer quit working years ago, but keeping up with each tank of fuel added the car should have somewhere around 400k miles on it. Based on my understanding having the chain off by 1 tooth would result in 18 degrees difference, and valves would have been impacting pistons long ago. Car runs fine, camshaft sprocket teeth look perfect, and the engine is remarkably clean and completely sludge free. Regular oil & filter changes.

To my knowledge, and the examination of 20 years of service records that came with the car, the engine has never been worked on except for a set of glow plugs in the past.

On the basis of an estimation of 1* of chain stretch per 100,000 miles I shoud be at 4 or 5 degrees at this mileage. I know that the TDC arrow indicator has some adjustment to it, but it appears to have never been moved from the dirt marks on it, and I also do not think it would have more than 2* movement in it either way. The balancer pulley cannot be off because of the factory centering pin.

The paper/tape markings are exactly spot on when viewed from above. They are elevated on the metal of the dampener and mounted on a larger diameter wheel, when you look at 20 & 30 degrees in the photo you are not looking strait down in a line of sight. If it were rotated with the 20 mark or the 30 mark strait up, and a new picture uploaded you would see what I mean.

Original question is why is there any measurement before TDC and not after. Even the MB manual states that a new chain should show 2* or so after 20,000 miles on a new chain after the initial break in period. This means that even with a chain that exhibited no wear it is still 4.5* off at the bare minimum, and I don't think that the timing pointer can even move more that about plus or minus 2*. This also doesn't take into account 400,000 miles.

thoughts?
ideas?
theories?
timing chain shrinkage?