We're trying to diagnose a 1990 300TE4Matic, 3.0 straight-6 SOHC 4-valve that started running like crap. It's gutless, and can barely get out of its own way. Started by checking the usual suspects... main and "differential" fuel pressures are within specs, ignition parts are good, timing is okay (crank-triggered), cat doesn't seem to be plugged, etc, etc.
While checking all that other stuff, we noticed some clattering coming from behind the distributor cap that sounded like a loose timing chain, so we popped off the distributor and valve cover to see if maybe the chain had jumped a tooth. However, the only sources we have to verify the timing marks are being very unhelpful, and basically giving the same useless info.
They all say to set the crankshaft at #1 TDC, which we did using the metal pointer that is part of the same bracket that holds the crank sensor pick-up.
Then they say "Ensure timing marks on camshaft and bearing cap are aligned", and show a drawing of the backside of the cam gear bearing flange... http://www3.telus.net/neatcrap/300TE/topview.gif
The bearing cap has the appropriate "mark" (big tab in the casting), but the back of the cam's flange doesn't have a nice big mark as shown. What it does have is two BIG bosses located 180degrees apart (which look more like cast-in handles for manufacturing), a smaller boss located between the two big bosses (looks like a much thinner version of the big bosses, that's been filed down to almost nothing, possibly a casting line), and a tiny dot on one of the cam's "ribs". The big bosses do not line up with the caps's mark (6 teeth before it), the smaller boss doesn't either (3 teeth after it), but the tiny dot DOES line up. (Note: pic is NOT at TDC (about 180 out), but I've shown where our marks are). http://www3.telus.net/neatcrap/300TE/back-of-cam-flange.jpg
Our sources also show drawings of the front of the timing components, with a "timing mark" on the left side, apparently level with the top of the head... http://www3.telus.net/neatcrap/300TE/frontview.gif
Our gear also has a mark in the same place when at TDC (pic out about 180), but since the gear can be flipped front-to-back if necessary to alter the timing by 3 degrees, the arrow may just point to the oval hole for the oval pin. Didn't look at the back to see if there's another arrow... http://www3.telus.net/neatcrap/300TE/front-of-cam-gear.jpg
So the problem is, we have no cam tab, a dot that's not mentioned anywhere, and none of the sources explicitly say if the arrow should be level with the head at TDC, so we can't be sure if it's still in time or not.
(Cross-posted to alt.autos.mercedes and rec.autos.tech)
I am working on a 1989 300te. Replaced the head gasket, and a broken timing chain. I am currently trying to set the timing. It looks to me like the 'tiny dot' is a timing mark. Aligning that with the one on the bearing cap puts the 'timing mark' on the gear in the right place (if you trust the image of the front of the engine included in your post, aligned with the head.) The big bosses can't be relied upon as markers because they are basically identical and 180 degrees apart (at least one of them will have to be wrong.) There is not a 'timing mark' on the other side of the gear. Also, the valves at cylinder one appear to be closed when the 'tiny dot' is aligned with the bearing cap mark. At any rate, I can't find any other information out there. So, I'm going with this 'tiny dot' scheme. I will post once it's back together to let you know the results.
"Merc300te" wrote: > I am working on a 1989 300te. Replaced the head gasket, and a broken > timing chain. I am currently trying to set the timing. It looks to me > like the 'tiny dot' is a timing mark. Aligning that with the one on > the bearing cap puts the 'timing mark' on the gear in the right place > (if you trust the image of the front of the engine included in your > post, aligned with the head.) The big bosses can't be relied upon as > markers because they are basically identical and 180 degrees apart (at > least one of them will have to be wrong.) There is not a 'timing mark' > on the other side of the gear. Also, the valves at cylinder one appear > to be closed when the 'tiny dot' is aligned with the bearing cap mark. > At any rate, I can't find any other information out there. So, I'm > going with this 'tiny dot' scheme. I will post once it's back together > to let you know the results.
Woo-hoo! Somebody else with the same problem!
We've also decided to go with the tiny dot. Although it's a bit loose, there doesn't seem to be enough slack in the chain to allow it to jump a tooth, so after a new chain and tensioner (ordered the parts, might as well put them in), we'll keep looking for the "runs like crap" solution.
> "Merc300te" wrote: > > I am working on a 1989 300te. Replaced the head gasket, and a broken > > timing chain. I am currently trying to set the timing. It looks to me > > like the 'tiny dot' is a timing mark. Aligning that with the one on > > the bearing cap puts the 'timing mark' on the gear in the right place > > (if you trust the image of the front of the engine included in your > > post, aligned with the head.) The big bosses can't be relied upon as > > markers because they are basically identical and 180 degrees apart (at > > least one of them will have to be wrong.) There is not a 'timing mark' > > on the other side of the gear. Also, the valves at cylinder one appear > > to be closed when the 'tiny dot' is aligned with the bearing cap mark. > > At any rate, I can't find any other information out there. So, I'm > > going with this 'tiny dot' scheme. I will post once it's back together > > to let you know the results.
> Woo-hoo! Somebody else with the same problem!
> We've also decided to go with the tiny dot. Although it's a bit loose, there > doesn't seem to be enough slack in the chain to allow it to jump a tooth, > so after a new chain and tensioner (ordered the parts, might as well put > them in), we'll keep looking for the "runs like crap" solution.
I put it back together, and after charging the battery have been trying to start it. The vehicle sounds like it's going to start but does not. Spark is occurring, and it seems to be getting fuel. There may be a fuel pressure issue, though it did not have one before taking on this job. Let me ask you, Masterblaster, when you line up the TDC sensor point on the wheel with TDC sensor, do you end up with the arrow aligned on the left with the head? I'm wonedering if my timing is off by a few teeth.
"Merc300te" wrote: > Let me ask you, Masterblaster, when you line up the TDC sensor point > on the wheel with TDC sensor, do you end up with the arrow aligned on > the left with the head? I'm wonedering if my timing is off by a few teeth.
With the wheel's mark and the pointer lined up, the tiny dot on the cam is in line with the boss, and the arrow is just like in the drawing; even with the top edge of the head: http://www3.telus.net/neatcrap/300TE/frontview.gif
Thank you for the thorough responses. Models after 1986 use the dot to set the timing on the cam. There are no markings on my harmonic balancer or crankshaft pulley. So, I had initially used the tab (which I assume the crankshaft position sensor uses to determine the crankshaft position) lining it up with the hole where the sensor resides. I do have tick marks, but the labels for the degrees are rubbed off. I have adjusted the timing by aligning tick marks with the pointer. But, I can't be sure which mark corresponds to '0'. I made the assumption that the degree mark nearest the 'tab' is '0'. This does not seem to be the case. Nor, is the one following that.
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