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

Rick Miley · #7 11-03-2004, 12:47 PM

If you're reading 20 degrees, then something is seriously wrong. But when you get closer take a peek at what I said here about the "line up the marks" method of timing.

Old300D · #8 11-03-2004, 01:03 PM

Quote:

Originally Posted by P.E.Haiges

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

I think you are right. From Rick's posted links, Larry Bible said this:

Quote:

You CANNOT check the chain on this engine by pulling on the chain to guess at the slack. The tensioner tightens the chain as it wears. The procedure, however, is quite simple.

You will need a 27MM socket that you can get on the crankshaft pulley centerbolt.

Turn the engine until you start seeing the timing marks on the harmonic balancer. Once you see the marks, turn very slowly until you are exactly at TDC. Look at the notch on the camshaft and see if it is lined up with the mark on the front camshaft mount. If you don't see the mark on the camshaft at all, turn the crankshaft one complete turn and set it at TDC again. You should then be able to see the mark.

If the engine has had frequent and religious oil changes, the mark on the camshaft will be lined up perfectly with the mark on the mount. If not, the mark will lag, and will not quite have made it to the mark on the mount. If it is lagging by more than a couple of degrees, it is time to roll in a new chain.

I did this exactly. Now I could have continued to turn the crank pulley to center the marks, but I estimated my timing pointer would have read 2-3 degrees - the cam mark and and notch were that close.

tomm9298 · #9 11-03-2004, 01:45 PM

Ok, it appears I have 10 plus degrees of stretch. I have never replaced a timing chain, only belts. I have read skinnerbox and still have a few questions. Have also read my Haynes manual. I do not have a MB manual on CD, I run Linux OS, not Microsoft. It seems to do the job properly, in regards to my mileage, 272k, I should replace all rails, guides, and the chain tensioner. I do not have and cannot afford the MB chain crimping tool. But, I have seen referances to links with 2 small "c" or "e" clips to hold the new master link. Are these junk master links? When rolling on the new chain, is this a 2 person job? The only way to turn the engine is with the crank pully, 27mm bolt. If it is a 2 person job, I will have to beg my wife to assist me. How much "fun" is it to tear down the front of the engine for rail/guide replacement? I would prefer to do it all, not just the chain and then have a guide break and destroy everything.

Pete Burton · #10 11-03-2004, 01:47 PM

...And as leathermang has dutifully stated numerous times, the best way of all to check the timing is to neutralize the valve lash on #1 intake and check timing @ 2mm valve lift. The spec for my engine (617.951) is 9.5 degrees with a new chain. I checked it 3 times during my rebuild. 10, 10, and 10 degrees. This takes into account all of the accumulated error.

Eskimo · #11 11-03-2004, 02:38 PM

Quote:

Originally Posted by tomm9298

I do not have and cannot afford the MB chain crimping tool.

You might check this thread, where BrierS generously offered to rent his super-nice crimper with what I consider to be very reasonable terms.

I'll be watching replies to your timing chain replacement questions, as I'm giving some thought to the same job myself.

tomm9298 · #12 11-03-2004, 04:24 PM

Thanx again guys!!! One more question. I have seen timing chains running from 38.79 (********) to 109.27 (FastLane). This seems to be a WIDE variance in prices. ******** has a Beck/Arnley chain P/N 0240044. Seventy dollars is a lot to save unless it is inferior. Any comments on the Beck/Arnley will be appreciated.

tomm9298 · #13 11-03-2004, 05:19 PM

I LOVE this forum!!!! BrierS is renting me his crimper.

engatwork · #14 11-03-2004, 05:38 PM

Keep in mind that you can do just a good a job crimping the link with a ball peen hammer BUT the tool does make the install easier

.

I'm still not convinced that your pointer ain't screwed up somehow unless someone is running a offset key in the cam sprocket

. 20+ degress is not right. Heck, you could move the chain a tooth and eliminate about 18 degrees of that (if memory serves me right). I imagine you will want to address your IP timing after you install the new chain. Do a search on here about using tie wraps to hold the chain on the cam sprocket. Pretty straight forward one man job if you take you time with it. good luck

leathermang · #15 11-03-2004, 06:20 PM

A lot of people come up one tooth off when doing a new chain... I think this is because the instruction about ' keeping tension' on the chain is not followed.

While the chain crimping tool is certainly a nice thing to have... .I don't know how many times Larry Bible and I have said that a hammer and centering punch and a hammer for an anvil will do a fine job on the chain pins.