M104 engine: Timing issue -one for the GURUS
 

I am in the middle of changing the head gasket on my m104 engine (300e 2.8 1993). I am very familiar with the correct way to set the timing as i have been researching it extensivly. so today i take a shot at installing the chain. i insert the 4mm drill bits in the correct locations on the cams. i made sure that the engine is at TDC, and that the drill bits are flat with the surface, i also retard the engine by rotating the cam-follower clockwise until it stops. i put on the chain making sure it is all tight, and then before installing the tensioner, i rotate the engine one full rotation to check.

here is what happens after 1 full rotation. the intake cam dowel (where the drill bit goes in) is slightly higher than the surface of the head. the one on the exhaust side is slightly lower than the head surface...


so what is the possible cause/ remedy for this ? am i a tooth off ?

thanks,

picture to see how far off?

The last M104 I did was ever so slightly off @ the cams but it was less then a degree or two. I attributed that to around 225K worth of wear on the timing gears etc..

Jonathan

No picture now as i took it apart to redo it tomorrow,,,,,basiclly, the exhaust side you cannot instert the drill bit as 2/3 of the hole is under the level of the head. of the intake side about 4-6 mm higher than the surface....

could it be a problem with the TDC location? although i made sure i put it right a number of times, and when removing the head, the first and last pistons were at cylinder head level.....

car is at 180,000 miles, but everything in there looks pristine :)

I will post a picture tomorrow ..

TDC is really hard to screw up for a number of reasons..the damper only goes on one way for one...

Did you mark your chain/gears etc before you removed them? I like to put everything back on the exact tooth it came off of...that way Everything lines up exactly as it came off the engine.

Is your cam actuator still @ full retard? Either way, it Sounds like you are doing everything right.

I did mark the chain, but the marks are irrelevant because the timing was not right to start with. there was no damage or anything, but originally the alignment of the cams was all wrong (the same issue but even worse!!!). the car had a head-gasket done from what i could tell sometime in the past, and i think they did not know how to align it properly....

anyway i could fix this issue?

bump for an answer!

My experience with both my 104 head gasket replacements:

After cranking through several turns, the timing alignment holes were within about two fifths of a hole diameter of spec. Indexing the chain one tooth either way would have created a larger off spec condition. I attributed the very slightly off spec condition to chain stretch and gear wear. Also, if you had the head resurfaced, the distance between the cams and crank will be very slighlty reduced but this difference is probably not measurable.

Without a pressurized chain tensioner in place, there is a fair amount of slack in the chain. If you had to back off slightly to position the crank at TDC, some of this slack will be between the crank sprocket and the intake cam sprocket. From my limited experience, this slack can easily result in about a "half a hole" off spec condition. You can experiment with this by positioning the crank at TDC, and then using a wrench to very slightly turn the cams. This is what finally convinced me that I was on spec. If you do this, be careful not to wrench the cams to hard--you don't want to rotate the crank. Just turn enough to take up or create chain slack. Keep in mind that the position of the intake cam can change relative to the intake sprocket because of the advance/retard gear.......

Disclaimer: I am a hobbiest mechanic, not a professional technician..... The above is based on my (limited) experience. There are others on this board that have far more experience, If I have given any wrong information or advice, I hope they will comment......

J. M. van Swaay

Just reread your first post. The condition you describe is consistent with chain stretch as both cams need to turn just a bit further to be on the marks. Don't know if it makes a difference, but was the drivers side chain guide pinned in place when you did this? I can't remember if the guide creates a longer chain run. If it does, that would advance both cams slightly thereby bringing you closer to an on spec condition.

J. M. van Swaay

thanks for the feedback.

it is actually quite off, i would say roughly 10 degrees higher on the intake side, and about 3-4 degrees lower on the exhaust side.....

i feel that there is a half-a-tooth slack somewhere....

here is my TDC mark ( i have my doubts about this, since the pointer is different than the one pictured in the factory cd)

http://img44.imageshack.us/img44/713...inework035.jpg http://img44.imageshack.us/img44/lat...jpg/1/w640.png

here are pictures before i took it apart. i have moved on since to drill bits for better accuracy....notice the difference in intake and exhaust cams

http://img33.imageshack.us/img33/106...inework038.jpg http://img33.imageshack.us/img33/lat...jpg/1/w640.png

lower on the exhaust side ^^^^^

http://img23.imageshack.us/img23/305...inework039.jpg http://img23.imageshack.us/img23/lat...jpg/1/w640.png

way higher on the intake side ^^^^^^

http://img195.imageshack.us/img195/9...ugust10066.jpg http://img195.imageshack.us/img195/e...jpg/1/w480.png

head is off in this picture. I think my TDC setting is accurate.....

J.M, my guide on driver's side was in place minus the pin.....it should not be a problem ...

i am confused

I'm not 100% sure here, but In the first picture I think you have the crank set at 10 degrees, not TDC............... Was this the crank position when you checked the cam dowels?

Both my cars have the same pointer as yours and I remember spending some time determining just where TDC was.

J. M. van Swaay

interesting, Where would the correct TDC location be?

I went by this http://www.ps2cho.net/downloads/MB%20CD/W124/w124CD1/Program/Engine/104/05-2230.pdf

the metal pointer should be exactly at the dash between 0 and T , unless i am mistaken.......

edit: yes, that is the position on the TDC i used to align the dowels..

http://img44.imageshack.us/img44/145...inework037.jpg http://img44.imageshack.us/img44/lat...jpg/1/w640.png

better picture of TDC

Its slowly coming back to me now. The TDC mark is confusing. I think I finally determined it by looking at the 1 I 0 2 I 0 3 I 0 on both sides of TDC, then finding the center between them. If my memeory is correct, TDC looked like this 0 I T (a T instead of a 0 on the right side of the hash mark)

J. M. van Swaay

(I'm getting a bit nervous here, keep my disclaimer in mind)

The hole in the indicater tab should be centered over the 0 I T

Are you sure about this? that was my initial impression, and i mentioned that on the benzworld forum where i have a progress thread over there...got my ass kicked as everyone was saying that the pointer (the metal tab) is the correct location, not the circle. my picture of the head removed also was taken with the TDC mark set as in in the picture: 0IT with the I exactly at the pointer......

my fear is that since this 1993 year does not have a TDC sensor upfront, that it could be a special case when in comes to TDC mark ...

anyone else have any experience with this?