M104 engine: Timing issue -one for the GURUS - PeachParts Mercedes-Benz Forum

latief · #1 08-25-2009, 05:29 PM

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,

jhodg5ck · #2 08-25-2009, 05:46 PM

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

latief · #3 08-25-2009, 07:31 PM

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 ..

jhodg5ck · #4 08-25-2009, 08:02 PM

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.

latief · #5 08-25-2009, 09:23 PM

Quote:

Originally Posted by jhodg5ck

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?

latief · #6 08-26-2009, 08:35 AM

bump for an answer!

J. M. van Swaay · #7 08-26-2009, 09:41 AM

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

J. M. van Swaay · #8 08-26-2009, 09:56 AM

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

latief · #9 08-26-2009, 10:41 AM

Quote:

Originally Posted by 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)

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

lower on the exhaust side ^^^^^

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

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

J. M. van Swaay · #10 08-26-2009, 11:14 AM

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

jhodg5ck · #11 08-26-2009, 04:43 PM

2X checking in WIS for the 2.8 M104 and it wants you to use the pointer for TDC over the 0 degree mark.

Jonathan

latief · #12 08-26-2009, 04:54 PM

Quote:

Originally Posted by jhodg5ck

2X checking in WIS for the 2.8 M104 and it wants you to use the pointer for TDC over the 0 degree mark.

Jonathan

Jonathon,

thanks for the help. can you explain what WIS is? i assume it is mercedes shop manual...how accurate is it in these situations..?

J. M. van Swaay · #13 08-26-2009, 05:50 PM

Jonathan, does the WIS show the same pointer picture as the one shown at this link:

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

J. M. van Swaay

latief · #14 08-26-2009, 04:52 PM

Thanks guys....

notice that the car was originally like this before i took apart.....something does not add up here.

logically, slack or no slack should not make a difference with a hand rotation. it is the count of chain pins (pieces) between the different sprockets that should count, or am i wrong on this?

If i use the pointer (which is not easy to use since it is not really a pointer), the timing is off after two rotations, and significantly....

dhaghighi, can you post a picture of your TDC mark on the crank please !

thanks

jhodg5ck · #15 08-26-2009, 06:04 PM

WIS is the Workstation Information System..getting mine courtesy of mercedes @ startekinfo.com (handy esp. for the updates/info on the new bits)..

JM, yes, same picture

Jonathan