1971 W109 3.5 timing chain stretch *degrees

[werminghausen]

I tried to measure the stretch of my chain last night (no idea how many miles the engine has, not well maintained anyhow, no records) and I found that I might have 8 degrees of stretch? Is this possible? or did the chain jump a tooth?
I had a hard time to find the zero mark on the crankshaft balancer (I marked it with a white dot) and on the cam sprockets. The marks on the left side are a bit vague. Interestingly the marks left and right cam are lining up fairly well while in theory if the chain is longer then left and right cam shouldn't align well?
I try and attach some pictures. Cam shafts don't look too bad actually.
I intend to change chain, tensioner and the upper rail guides.
Any comment is good, please...
Martin

[GGR]

Make sure the tensioner is pushing on the guide when you take your measurement.

Cam sprockets have 36 teeth so each one represents 10 degrees. Knowing the crankshaft must do two revolutions for the camshafts to do one revolution, repositioning both camshafts by one tooth will put you 5 derees closer to the mark at the pulley. But you will stil be off by 2.5 to three degrees. This can be taken care of by offset woodruf keys.

Before anything, you should make sure your pulley is properly positioned: put a screwdriver in the cyl.1 spark plug hole anf look for tdc. then check if you're on the 0 mark at the pulley.

Also before ordering offset woodruff keys make sure that your engine does not have some installed already. For 2 degrees difference on the crankshaft you have to order 1 degree offset woodruf keys.

[werminghausen]

Thanks so much, this is interesting.
First I'll make sure Cylinder 1 is exactly in TDC position (i have a dial gauge). Then I'll make sure the chain is under tension (which I think it is) and see if things turn out the same.

Does my engine (3.5) have marks on both camshafts for TDC? I was not sure about the left side at all. Well if there is a mark on the sleeve bearing, then it would be not engraved but upstanding line?

In theory if it does turn out being the same 8 degrees difference there might be 2 options. Option 1 the chain is streched so much causing 8 degrees difference- Is this possible? I mean realistically can this happen without really damaging the teeth of the sprockets?

Option 2 would be that the chain slipped one tooth creating a 5 degree difference plus a stretch of 3 degrees.

What do you think?

How can I find out if this engine has the 'shims' installed offsetting chain stretch.

Are you recommending changing the chain and tensioner?

Martin

[Tomguy]

Originally Posted by GGR

Make sure the tensioner is pushing on the guide when you take your measurement.

Cam sprockets have 36 teeth so each one represents 10 degrees. Knowing the crankshaft must do two revolutions for the camshafts to do one revolution, repositioning both camshafts by one tooth will put you 5 derees closer to the mark at the pulley. But you will stil be off by 2.5 to three degrees. This can be taken care of by offset woodruf keys..

You divided by two. Since the crank moves twice as fast as a cam not half, 10 at the cam > 20 @ the crank. Moving a tooth on the chain is never right. 8 isn't too bad. I had about 12 doing mine. BUT it does mean you need a new chain. Roll it in. Your existing sprockets should be good. If your guides are solid plastic replace them. If they are aluminum with a hard rubber surface DON'T!! Do the tensioner rail as new ones are still aluminum.

PS your other timing mark on the tower is on the inside of it.

[werminghausen]

Originally Posted by Tomguy

You divided by two. Since the crank moves twice as fast as a cam not half, 10 at the cam > 20 @ the crank. Moving a tooth on the chain is never right. 8 isn't too bad. I had about 12 doing mine. BUT it does mean you need a new chain. Roll it in. Your existing sprockets should be good. If your guides are solid plastic replace them. If they are aluminum with a hard rubber surface DON'T!! Do the tensioner rail as new ones are still aluminum.

PS your other timing mark on the tower is on the inside of it.

Hi Tomguy: great math- you are right! It can't be a tooth off. It must be stretch and if you say 8 degrees is not too bad- then fine.
The sprockets are not looking too bad.
I checke with the fine dial gauge today the zero mark on the crank. Absolutely perfect match. piston of #1 TDC is exactly at the Zero mark on the crank.
Two things I need to know: What new parts do I need?
1) 1 chain
2) 1 tensioner
3) 1 tensioner rail....I guess this is the big guy where the tensioner is pressing at
4) 3 guide rails. Why not change when they are aluminum/rubber- I want to understand
5) I also change the plastic lube rails parts for the cam as I am there now.

questions:
a) Why not change when guides are aluminum/rubber- I want to understand
b) What are these woodruf keys and how can I see if something like that is in the engine?
c) marks on camshaft: what do you mean with...your other timing mark on the tower is on the inside of it?
I have clear marks on the right side cam (sprocket and bearing).....while the left side is a bit unclear....well there are a couple marks on the bearing..the one moving on the sprocket is clear...same as on the left side.

[Tomguy]

a) They are higher quality. Many engines have died due to failure of the plastic rails. Replacement is because the plastic rails get brittle and crack, causing the chain to jump, which makes valves kiss pistons. Bad situation that can be avoided by using rails that do not crack.
b) The woodruff keys are on the camshaft itself. They are used to hold the gear to the cam. Factory uses non-offset keys. I would advise against changing them. Usually they need to be changed if the head is planed causing a smaller distance of chain, that affects the geometry to the point they are needed.
c) I'll see tomorrow if I can dig up a pic.

[werminghausen]

Originally Posted by Tomguy

a) They are higher quality. Many engines have died due to failure of the plastic rails. Replacement is because the plastic rails get brittle and crack, causing the chain to jump, which makes valves kiss pistons. Bad situation that can be avoided by using rails that do not crack.
b) The woodruff keys are on the camshaft itself. They are used to hold the gear to the cam. Factory uses non-offset keys. I would advise against changing them. Usually they need to be changed if the head is planed causing a smaller distance of chain, that affects the geometry to the point they are needed.
c) I'll see tomorrow if I can dig up a pic.

Thanks Tomguy
I looked up the woodruff key. It is a halfmoon key- ok understood. didn't know the term. Ao the adjustable one is using an offset within the rectangular section of the key?.....wow....in order to adjust some 2 degrees in crank movement?
If you can give me some hint where the marks are- great.
I think I understand what the issues are now.
Another question: If I can correct the offset of valve timing (now approx. 8 degrees) and align the cams to the crankshaft do I need to adjust the ignition timing or do you think this should be all good?

[mercmad6.3]

Originally Posted by werminghausen

I tried to measure the stretch of my chain last night (no idea how many miles the engine has, not well maintained anyhow, no records) and I found that I might have 8 degrees of stretch? Is this possible? or did the chain jump a tooth?
I had a hard time to find the zero mark on the crankshaft balancer (I marked it with a white dot) and on the cam sprockets. The marks on the left side are a bit vague. Interestingly the marks left and right cam are lining up fairly well while in theory if the chain is longer then left and right cam shouldn't align well?
I try and attach some pictures. Cam shafts don't look too bad actually.
I intend to change chain, tensioner and the upper rail guides.
Any comment is good, please...
Martin

8 degrees is normal for a worn out chain. I have seen up to 15 degrees on noisy engines . 5 degrees is really about as far as you should let an engine go before changing the chain. Usually once the chain has gone beyond 5 degrees the tensioner needs to be measured too . if it fails to meet limits,it needs replacing.
The arm ( or cover, if available near you ) on the tensioner needs replacing at the same time but on the early M116 the chance of worn top rails is pretty remote. The plastic ones don't wear either ,just break down with age .
BTW,the damper should be marked with 0 I 0 to indicate TDC. It's very very unusual for the damper to fail on these engines and for the marks to be incorrect. So it's OK to use the mark without worrying about the damper having moved,as on a Chev etc.

[GGR]

Oooops!!!! Indeed, 10 degrees at the camshaft equals 20 degrees at the crankshaft. Sorry for misleading you.

Usually you see the stretch best on the passenger side camshaft (on A lhd).

[mercmad6.3]

Also, turn the engine while watching the cams,line the Cam marks up with cam tower mark Then look at the damper mark. Doing it this way you get the slack in chain giving you the correct reading showing the wear.

[werminghausen]

Originally Posted by mercmad6.3

Also, turn the engine while watching the cams,line the Cam marks up with cam tower mark Then look at the damper mark. Doing it this way you get the slack in chain giving you the correct reading showing the wear.

'line the Cam marks up with cam tower mark' : Where are cam marks and where are tower marks, can you explain this so I can understand?

'Then look at the damper mark': What is the damper mark. is this the crankshaft mark?

I mean I showed the pictures in the beginning (crank at 8 degrees after TDC, both cams lining up. What is wrong here? Martin

[mercmad6.3]

on each cam bearing (tower) is a line ,about 10 mm long x 1 mm wide. On each cam gear is a washer with a notch. Line the notch with the line,then look at the damper,it's the round thing on the front of the crank. where the pointer is aimed,is the amount of wear in the chain. ideally it should be less than 5 degrees.

[Tomguy]

Basically (since it can get tricky AND engine compression can cause crank movement throwing the reading off):
1) Pull the plugs
2) Rotate the CRANK (clockwise from front) until the ENGINE RIGHT (left side as seen from the front, right as you would view it from the driver's seat and technical specifications, US pass side) cam alignment mark is spot-on.
3) Read (or take a picture of) the timing mark on the hub. Your goal is within a few degrees of TDC. When I replaced my chain, I was at about 1-2°. Prior I was at 12°.

This is the best pic I could find. This is what I mean by on the "Inside" (cam side) for the timing mark.

[werminghausen]

Originally Posted by Tomguy

Basically (since it can get tricky AND engine compression can cause crank movement throwing the reading off):
1) Pull the plugs
2) Rotate the CRANK (clockwise from front) until the ENGINE RIGHT (left side as seen from the front, right as you would view it from the driver's seat and technical specifications, US pass side) cam alignment mark is spot-on.
3) Read (or take a picture of) the timing mark on the hub. Your goal is within a few degrees of TDC. When I replaced my chain, I was at about 1-2°. Prior I was at 12°.

This is the best pic I could find. This is what I mean by on the "Inside" (cam side) for the timing mark.

Your picture is from the left side cam (driver side) of a 3.5? If so: my picture that I showed in the beginning is the same...only the marks are not so clear as in your pic. Interestingly (and if my pic from left side shows the marks aligned) left and right side marks are lining up perfectly at 8 degrees after TDC.
I was wondering why this happens, because the stretch should also make left and right side dis-align meaning if for instance right side cam is aligned then the left should be dis aligned?
Thanks Martin

[werminghausen]

Originally Posted by Tomguy

a) They are higher quality. Many engines have died due to failure of the plastic rails. Replacement is because the plastic rails get brittle and crack, causing the chain to jump, which makes valves kiss pistons. Bad situation that can be avoided by using rails that do not crack.

Hi Tomguy
Thanks so much to all of you for the informations.
I examined the guide rails. They are ALUMINUM- all of them.
You say leave them. Martin