W123 Timing Chain Stretch - PeachParts Mercedes-Benz Forum

tomm9298 · #1 11-03-2004, 10:42 AM

I need to know if I am doing this right. I turned the crank until my pointer was lined up with the pin. I assume TDC. With the valve cover off I check my cam timing marks. The spacer mark was about 1/8 inch before the cam tower mark. I continued to turn the crank until my cam timing marks were aligned. I then check my crank pointer, it was at about 20 deg BTDC. I rotated the engine 1 revolution and my cam timing marks were no longer visible, on the spacer/washer that is. I turned the crank another revolution and the cam marks were the same, not lined up. Does this mean I have 20 deg of chain stretch????

Eskimo · #2 11-03-2004, 11:11 AM

No offense, but hasn't this been thrashed pretty well in your existing thread? It seems to me that psfred's tried to address your questions pretty thoroughly, and that it might come down to actually having to confirm whether the timing mark on the pulley is really properly representing the rotational position of the engine (i.e., is it pointing at TDC when the piston is physically at TDC).

He suggested feeling for when the piston stops pushing air past your thumb on #1 cylinder glow plug hole. I've never tried it, but I imagine one could rig up something (maybe even as simple as a rubber stopper with a hole in it) to connect to the glow plug hole that would allow connection of a length of clear plastic tubing. Then, one could rotate the engine to a bit before the expected TDC position, dip the free end of the tube into a plastic soda bottle with a bit of water in it, then slowly rotate the engine until the bubbles just stop (and then disconnect the rig from the glow plug hole so as not to be able to pull any water up through the tube into the cylinder).

Just a notion, never tried it, but something like that might be a reasonable compromise between "thumb on the glow plug hole" and "pull prechamber and feel the piston position with a probe".

P.E.Haiges · #3 11-03-2004, 11:28 AM

Tomm,

Isn't 18 degrees the amount when the chain is off by one tooth?

Usually if the chain is off by one tooth, the valves hit the pistons. So Eskimo may be right about the timing mark being off. This would mean that the vibration damper has slipped, possibly the woodruf key has sheared.

Its not too much work to pull the damper to check the woodruf key, but do any easy checks first to determine if the damper has slipped.

P E H

tomm9298 · #4 11-03-2004, 11:38 AM

I looked for my original thread and thought it was deleted, must have missed it..?? I will look to see if anything has been moved/adjusted. I will pull the glow plug and watch for piston TDC. The engine does not smoke and has good power. Will update later. Thanx....

Old300D · #5 11-03-2004, 12:05 PM

I checked for chain stretch last weekend, while I was adjusting my valves. I turned the crank to point to 0 degrees, noticed both the cam lobes for #1 were off the valves, and looked at the cam sprocket. The notch and the mark were within half the width of each other, and I called it good. What is that, about 2-3 degrees? My engine, used, from a scrap yard, presumably has about 150k miles on it.

P.E.Haiges · #6 11-03-2004, 12:10 PM

Old300D,

You checked the timing backwards. You should line up the timing marks on the cam and read the degrees off on the damper.

P E H