Replacing Timing chain, A couple of Questions.

[RadioTek]

Rolled in a new chain yesterday, followed the procedure at Mercedeswiki about the 3 pairs vice-grips. Everything went pretty smooth if you don't count the loss of one Oh Jeezus clip (E-clip for Chain master link) just a trip to NAPA for a replacement.

Now I have a couple of questions

1) What is the torque for the valve cover bolts? I know it's a rather low value to keep from warping the cover or stripping out the bolt hole.

2) When I started the process, I figured that I had about 16 to 18 degrees of chain stretch. I figured this by lining up the alignment marks on the cam and reading the difference from TDC on the harmonic balancer. After I got the chain replaced and in, I still have about 15 degrees of difference from TDC at the balancer, with both of the cams lined up perfectly.

Will this be taken care of when I fire it up by the chain tensioner? Or am I going to have to look for another cause? There are some of the typical notches in the heads from the old chain, and there were some light scratches on the inside of the Drivers' side valve cover from the chain.
Both cams line up perfectly with the new chain, but I have that 15 degree difference.

Thanks in Advance,
Scott

[BDBENZ]

Something bothers me about this, I replaced my chain and rails on my 87 as maintenance because of time. I did not want to risk the rails braking because of age. My chain stretch was 8 degrees and afterwords when all lined back up the timing mark was dead on 0. Are you sure you have the tensioner mounted correctly? When I installed mine I remember it being difficult to remount because of the tension it applied to the new chain. Before I started the car I rolled the engine over two times with the crank and rechecked my marks. I wood go back to the manual and recheck the tensioner procedure.

bdbenz

[rocky raccoon]

3 to 4 Nm. Use a 1/4" drive torque wrench to be in sensitive range.

[Graham]

Originally Posted by BDBENZ

Something bothers me about this, I replaced my chain and rails on my 87 as maintenance because of time. I did not want to risk the rails braking because of age. My chain stretch was 8 degrees and afterwords when all lined back up the timing mark was dead on 0. Are you sure you have the tensioner mounted correctly? When I installed mine I remember it being difficult to remount because of the tension it applied to the new chain. Before I started the car I rolled the engine over two times with the crank and rechecked my marks. I wood go back to the manual and recheck the tensioner procedure.

bdbenz

I think this is good advice.

I had a local shop install my chain. But they ordered the wrong tensioner, so just put the old one back. Next day I noticed some noise, but drove car a bit. then following day there was loud clanging. Opened engine and found passenger side marks off by about 8deg with new chain.

I ordered a new tensioner and installed it myself. Rotated engine a few times and checked - marks now within 1 or deg. Car has run fine since.

PS: I was told that new tensioner would not change timing marks, but it did.

[RadioTek]

I'm strongly thinking about going back in to recheck everything. I rotated the engine a couple of times (with a ratchet on the crank bolt) and it was stil the same. Since this is a '75 with the metal backed rubber tensioner rails, I didn't do anything to the tensioner.

I'm wondering if a previous owner did something that got the engine a tooth off somewhere. If the crank gear has 24 teeth, that would make it 15 degrees off if it jumped one tooth.

I wonder if it would be possible to adjust everything without having to pull the timing / dirstibutor drive gear off. Set the crank to TDC, move the cams one tooth in the correct direction and reset the distributor? As it is, the distributor is close to the end of it's adjustment slot to get it to fire at TDC.

What I need to know before I think about this any further is the number of teeth on the crankshaft gear and the cam gears. Does anyone have an engine apart that they could look at?? This is one of the cast iron block 450's with D-Jet injection.

I just hope that when I look back into it, everything is all right now. But my life doesn't work that way.

Thanks,
Scott

[rowdie]

I have my old gears out in the barn. When it stops raining I will go out and check. The CD states one cam tooth is approx. 18 degrees.

[Rafi]

If each tooth is 18 degrees then the sprocket has 20 teeth.
360 degrees/number of teeth = degrees/tooth

[rowdie]

I was only citing the CD. Went out and got the gears. Cam is 36 and crank is 18.

[Rafi]

36/18 = 2 so each turn of cranck, cam turns twice. All these make sense, there is no mystery.

[Rafi]

Sorry, I got it backwards for each cam turn cranck turns twice. More teeth slower speed or more angle/tooth faster turn.

[rowdie]

Originally Posted by Rafi

Sorry, I got it backwards for each cam turn cranck turns twice. More teeth slower speed or more angle/tooth faster turn.

That would explain the angle on the dist end of the timing gear. 30 teeth on chain, 10 on dist end. But they are all 360 degrees so why would alignment of the timing gear be critical?

Asking because after rebuild on my '73 450 I have a miss and low vacuum with no leaks I can find. Cams and timing are spot on.

I don't want to have to pull the engine again.

[Graham]

Originally Posted by RadioTek

I'm strongly thinking about going back in to recheck everything. I rotated the engine a couple of times (with a ratchet on the crank bolt) and it was stil the same. Since this is a '75 with the metal backed rubber tensioner rails, I didn't do anything to the tensioner.

The rail type does not have much to do with the tensioner. The tensioner takes up the slack in the chain. You do need to get some oil pressure to get the tensioner to actuate. Spinning with starter should do it?

BTW - It is usually recommended that you change tensioner when you change chain.

I have similar engine in my car and rails are still good, but tensioner was bad.

[Graham]

Originally Posted by rowdie

Asking because after rebuild on my '73 450 I have a miss and low vacuum with no leaks I can find. Cams and timing are spot on.

Have you checked AAV? If stuck open it is a huge vacuum leak. Try pinching off the hose between it and the idle valve.

[RadioTek]

Originally Posted by Rafi

36/18 = 2 so each turn of crank, cam turns twice. All these make sense, there is no mystery.

So at 36 teeth; I should be able to go two teeth on the cams to get it back close, then adjust the timing for the other 3 degrees to get to fire right. I think 3 deg is within tolerance. Anybody have any objections to this line of thinking? I'm picking brains here before I go trying to do something that may cause damage.

Thanks,
Scott

[Roncallo]

When checking timing it is very important to approach TDC in the clockwise direction only. If you overshoot then you must rotate backwards about 30° than re attempt to approach TDC in a clockwise direction. This is necessary because the tensioner is limp at this point and the cam will be free to rotate about 10° ahead of the actual crank position. Also it is necessary to watch the cam and make sure it does not shoot ahead of the crank position, due to the slack in the tensioner. This can happen because the cam lobes have a tendency to drive the cam forward or backward depending on position. To verify this make sure the chain is tight on the distributor side and loose on the tensioner side when checking the timing. If you are unsure of yourself you can remove the lifters and the problem gets greatly reduced.

The tensioner has really nothing to do with timing. It just takes up the slack and stabilizes the cam motion.