Chain Stretch on 81 240D - PeachParts Mercedes-Benz Forum

treiberg · #1 06-24-2010, 12:28 AM

This makes no sense. I am using the less accurate method of checking chain stretch (alinging marks on cam tower) just to get a rough idea of where things are at, and my result is perplexing. Take a look at the pic...instead of seeing my chain stretched, I am seeing my chain advanced! Normally the pointer would point to the marking to the left of the zero, mine points to the right of the zero about 10-12 degrees! What does this mean...something has slipped, or someone put a too big of a key, or my indicators are not positioned correctly??? What about that piece with the circle in it that is showing 20deg? I haven't seen that in other pics...all other pics show the pointed tab as the one to use to indiccate degrees? Not sure where to go from here.

Original symptom is bad vibration at idle, and have already replaced motor mounts and injector nozzles. Otherwise, car runs pretty good, gets very good mileage (30+), and starts right up, and no smoking. Seems like if the timing was this far off the car would run very badly, right?

Diesel911 · #2 06-24-2010, 12:55 AM

When you get an abnormal reading it is time to use the 2mm Method.

I have never seen a pointer like that and apparently it is adjustable?
Are you sure you are supposed to read through the Hole?

It also makes me wonder what type of reading a person could get if the Engine was rotated the wrong direction.

Diesel911 · #3 06-24-2010, 01:36 AM

In the above pic the one on the left is not aligned properly. The one on the Right is aligned correctly.

In the blow up of your pic the Green Arrow indicates the Direction of Rotation.
The Purple Arrow Indicates 10 degrees before Top Dead Center (10 degrees advanced)

The Red Arrow points to Zero Degrees = Top Dead Center

The Yellow Arrows point to 10 degrees and 20 degrees After Top Dead Center and this is Late/Retarded Timing.

I would try Rotating the Engine again and being extremely careful aligning the marks. I mean get you Eye right up next to the marks because if you are lookiing downward on it or at any sort of an angle it will throw the alignment off.

treiberg · #4 06-24-2010, 05:23 AM

I am more than willing to do the 2mm method, but would it really make such a different as going from 10-12 degrees advanced to being 0-5 degrees stretched? I did rotate engine properly (clockwise when standing at the front and facing the engine). I rotated the engine again being ever so careful to align marks and I get the same result.

My suspicion is that the timing pointer may be misaligned or bent (I am using the pointer, not the hole. Although the hole would indicate 20 degrees late, which would almost make more sense.) What would help to clear this up is to get a picture of the timing pointer from someone else's 240D of similar vintage (mine is 1981). I am hoping someone on the forum might be able to provide that.

leathermang · #5 06-24-2010, 06:52 AM

Quote:

Originally Posted by treiberg

I am more than willing to do the 2mm method, but would it really make such a different as going from 10-12 degrees advanced to being 0-5 degrees stretched? I did rotate engine properly (clockwise when standing at the front and facing the engine). I rotated the engine again being ever so careful to align marks and I get the same result..

Do you have a Factory Shop Manual for your car?
I am pretty sure you do not... or have not read it.
The FSM , which I have quoted many times on this subject, says that the cam tower marks are only for the initial assembly of the engine.. not to be used for this kind of measurement. That is why it explains how to do the 2mm method.
You really need a FSM to work on your engine....because it has lots of WARNINGS which never get posted when only using a forum...

Diesel911 · #6 06-24-2010, 12:10 PM

Quote:

Originally Posted by treiberg

I am more than willing to do the 2mm method, but would it really make such a different as going from 10-12 degrees advanced to being 0-5 degrees stretched? I did rotate engine properly (clockwise when standing at the front and facing the engine). I rotated the engine again being ever so careful to align marks and I get the same result.

My suspicion is that the timing pointer may be misaligned or bent (I am using the pointer, not the hole. Although the hole would indicate 20 degrees late, which would almost make more sense.) What would help to clear this up is to get a picture of the timing pointer from someone else's 240D of similar vintage (mine is 1981). I am hoping someone on the forum might be able to provide that.

IF the ponter is the one on the lower right it does look like it is bend down.
The issue is how do you bend it back properly?
I think you would have to find Top Dead Center; and this would mean using a Dial Indicator on the top of the Piston.

The easiest way would be to just get another pointer from the Junk Yard.

Diesel911 · #7 06-24-2010, 12:16 PM

On the Camshaft Alignment method verses the 2mm Method Brian Calrlton had a thread on that and I believe he said he had done both and that if you line up the markes correctly it is extremely close.
It is certainly good enough to give you an idea if you need to use the 2mm Method.
The main thing is that it is an easy check that you can do when you adjust your Valves of for some other reason have the Valve Cover off.

It also makes you wonder why the Alignment Marks are OK to use for assembly but not OK as a quick check.
I do not recall the FSM saying that after you did the inital alignment with the Marks that you were required to do the 2mm Metnod.
Perhaps they are assuming during a rebuild new parts would be used.

leathermang · #8 06-24-2010, 12:19 PM

Here is the procedure for finding the top of a piston movement...
You put something on the crank which can be marked on... and a pointer to that location..
Then you put the dial indicator on the piston top... hand turn through a couple of strokes and find the spot that looks like TDC... then on the next stroke mark a place on the crank and note the reading on the indicator... then continue the movement of the crank slowly until you find that distance movement on the downstroke... mark that place on the crank..
Half way between those two marks is the TDC movement of that piston... remember that happens twice per four cycle stroke.. so other things must be considered if you are needing TDC ON the Compression stroke for anything.. like IP timing...
The reason it is done this way is that at TDC the actual movment of the piston is way too small to tell when the crank throw is at the exact top spot. So you bracket it and take the distance half way between your measurements going up and down.

leathermang · #9 06-24-2010, 12:31 PM

Quote:

Originally Posted by Diesel911

On the Camshaft Alignment method verses the 2mm Method Brian Calrlton had a thread on that and I believe he said he had done both and that if you line up the markes correctly it is extremely close.
It is certainly good enough to give you an idea if you need to use the 2mm Method.
The main thing is that it is an easy check that you can do when you adjust your Valves of for some other reason have the Valve Cover off.

It also makes you wonder why the Alignment Marks are OK to use for assembly but not OK as a quick check.
I do not recall the FSM saying that after you did the inital alignment with the Marks that you were required to do the 2mm Metnod.
Perhaps they are assuming during a rebuild new parts would be used.

Generalizing to all cars based on Brian's experience on one or even several cars seems imprudent in the light of the FSM instructions as to how to correctly do it. Comparing them... great... but substituting based "?".
The fact that it is ' an easy check' as compared to an accurate one seems like squishy reasoning.
Are we now confined to what you can remember as compared to what is written in the FSM ?
LOL
The alignment marks are used to be sure the cam is in the right quadrant... and I promise you all this stuff is in the FSM....

treiberg · #10 06-24-2010, 01:13 PM

leathermang, thanks for the input, and yes I do understand that the timing marks are not very accurate, but keep in mind that what I am seeing looks to be 10-15 degrees off, which I would think is so far from normal, even with the less accurate method.

When finding TDC, I do understand marking on up and down and finding the midpoint, makes total sense. But how do you put the dial indicator on the piston top? (yes, I know it's in the FSM, but until I get my hands on one...)

Finally, where is the best place to get a FSM? I would like certainly like to invest in one.

whunter · #11 06-24-2010, 02:37 PM

Quote:

Originally Posted by treiberg

leathermang, thanks for the input, and yes I do understand that the timing marks are not very accurate, but keep in mind that what I am seeing looks to be 10-15 degrees off, which I would think is so far from normal, even with the less accurate method.

When finding TDC, I do understand marking on up and down and finding the midpoint, makes total sense. But how do you put the dial indicator on the piston top? (yes, I know it's in the FSM, but until I get my hands on one...)

Finally, where is the best place to get a FSM? I would like certainly like to invest in one.

To order technical literature call:
1-800 FOR MERCedes (1-800-367-6372)
http://www.startekinfo.com/StarTek/outside/8638/?requestedDocId=8638

Have a great day.

Diesel911 · #12 06-24-2010, 03:18 PM

Quote:

Originally Posted by treiberg

leathermang, thanks for the input, and yes I do understand that the timing marks are not very accurate, but keep in mind that what I am seeing looks to be 10-15 degrees off, which I would think is so far from normal, even with the less accurate method.

When finding TDC, I do understand marking on up and down and finding the midpoint, makes total sense. But how do you put the dial indicator on the piston top? (yes, I know it's in the FSM, but until I get my hands on one...)

Finally, where is the best place to get a FSM? I would like certainly like to invest in one.

I PMed where to get the Manual direct from Mercedes.
However, I do not recall reading in my FSM what to they recommend to do in the case of the Pointer not being correct. However, it may be in there.

I Just know that on other Enigines you can use a Dial Indicator to locate TDC.
In the case of Mercedes you would have to pull the #1 Pre-chameber to gain access to the top of the Piston. You would need a long indicator extenxion to get down there.
Like I said it would be easier to get a new or used un-bent pointer.

treiberg · #13 06-24-2010, 03:23 PM

Thanks whunter on the FSM.

I really think I just have a bent pointer (I am hoping all that I am dealing with). The other possibility is I am off a tooth somewhere. If the pointer is just bent, maybe I could bend it back once I know where TDC is. Or if I can replace that bracket that has the pointer on it, maybe that would work.

Still not sure how I can determine TDC without a spark plug hole above the piston. I am sure someone will chime in on that one.

(Diesel911 - You were writing your post as I was writing mine, looks like we are on the same page.)

whunter · #14 06-24-2010, 04:31 PM

Quote:

Originally Posted by treiberg

Thanks whunter on the FSM.

I really think I just have a bent pointer (I am hoping all that I am dealing with). The other possibility is I am off a tooth somewhere. If the pointer is just bent, maybe I could bend it back once I know where TDC is. Or if I can replace that bracket that has the pointer on it, maybe that would work.

Still not sure how I can determine TDC without a spark plug hole above the piston. I am sure someone will chime in on that one.

(Diesel911 - You were writing your post as I was writing mine, looks like we are on the same page.)

You have e-mail..

treiberg · #15 06-25-2010, 12:55 AM

Quote:

Originally Posted by whunter

You have e-mail..

Thanks for the email whunter!!

I am moving forward with my theory that somehow the timing pointer is bent. If I can imagine it bent back so the edge is square, that would put timing back very close to zero degrees, which is a huge relief. I think the little post on the balancer actually pushed that pointer back, like there wasn't enough clearance and it just grabbed it and bent it back. But to get an accurate timing mark, I need to either fix the bent peice or make my own mark. Knowing where TDC looks pretty involved from the FSM. So I am hoping that timing indicator can be replaced. It looks like it is just bolted on...can anyone confirm that? Or maybe I can just unbolt it and bend it back. (see pic)