Mercedes 300SD Timing Chain

Well, so far this forum has been awesome and I got my glow plug issues resolved! It turned out to be bad glow plugs and battery. However I am in a fix now.
When I bought the car it was leaking oil very badly so this past weekend I started the tedious process of tearing the motor down to replace the upper gaskets. The problem I am having is to do with the timing chain. I got the head removed from the car and in the process the timing chain fell down into the block. I managed to get it pulled back up through the block and head after I reattached it. The problem is when I put the chain back on the sprocket for the Cam shaft, the sprocket sits about 1/2" too low to fit back onto the shaft. I am wondering if the chain got a kink in it further in the block when the chain dropped in. I have tried manullay turning the motor and the chain does move but still not enough slack to get it back into place. Does anyone have any ideas on what needs to be done to get it back in place? Is there something on the lower half of the motor that I can open to get a look at the chain from below? This is my first diesel repair and it's prooving to be a challenege. Any help is greatly appreciated. Thank you!

-Brian

if you email with year/model/engine code-can send
diagrams of chain and timing process.

if you email with year/model/engine code-can send
diagrams of chain and timing process.

It is a 1983 300SD w/5cyl 3.0l Diesel. If you can tell me where to find the engine code, I will post it later tonight or tomorrow. Thank you!

-Brian

no listing on my uk data sorry.

i too had timming chain issues with my 300sd and mechy1barry was the man,
he was very helpful and generously patient in helping me solve the problem

while i was in the middle of this quagmire i discovered that the cam chain tensioning device must be removed to allow enough slack in the chain for a human to be able to complete the chain connection
and mechy1barry sent me a diagram that showed the timming marks on the back of the top sprocket that must be aligned with a mark on the cam bering tower while the crankshaft is @ tdc (top dead center)

i hope this helps :)

i too had timming chain issues with my 300sd and mechy1barry was the man,
he was very helpful and generously patient in helping me solve the problem

while i was in the middle of this quagmire i discovered that the cam chain tensioning device must be removed to allow enough slack in the chain for a human to be able to complete the chain connection
and mechy1barry sent me a diagram that showed the timming marks on the back of the top sprocket that must be aligned with a mark on the cam bering tower while the crankshaft is @ tdc (top dead center)

i hope this helps :)


Which one is the cam tensioning unit? This thing is driving me insane!!! Another question. Should I be able to turn the motor completely around using a wrench? I can get it to turn only so far in either direction before it locks up. Not sure if there is a kink in the chain causing it to jam inside the motor. One other thing too, how do I tell if the motor is at TDC now that I have tried tunring the crankshaft? Can I remove one of the injectors to see where the pistons are sitting? Any additional help would be greatly appreciated. Thanks!

if you are standing in front of the car looking at the front of the engine over the radiator the tensioning device is bolted to the left side of the block just under the thermostat housing (which must be removed for access) it is what holds pressure on the tensioning rail that in turn keeps the cam chain slack in check the tensioning rail is the curve shaped piece that rides directly against the chain just under the left side of the top gear.

and YES with the chain attached properly you should be able to turn the crankshaft around and around in a clockwise direction

I woud say that with the tensioning device removed and you still cannot attach the chain this would tell me that there IS a kink in the chain some where below. If this is the case get 1 person to GENTLY work the crankshaft back and fourth while another person pulls upwards on BOTH ends of the chain to pull out the kink.

do not try to force the crank past a LOCKED position because either a piston is wrecking into an open valve or the kink is binding against the block

i forgot there is tdc indicater bolted on the block @ about 2 oclock behind the harmonic balancer which has the lineup line on it, clean it off real good so you can see it well

Thank you very much for your input. I do know which tensioner you are talking about now. I won't be able to get over and try anything until late tonight or tomorrow. I will post what my outcome is. Thanks again!

wish I could have been of more help here guys,
but no info on this one-and I would not like to lead any one astray!! good luck.

depending on your mileage and the last time it was done, if at all, it might be a good time to roll a new chain in. good ol' tensioner hiding behind the thermostat huh?

Well, I got a chance to work on this some more yesterday with only minimal success. I removed the oil pan, and looking up inside I can see the timing chain still attached to the crank sprocket without any kinks in it. I also tried the moving of the motor back and forth and pulling up on the chain, this did not yeild any more length. As far as the motor locking while trying to turn it around, got that figured out and I can turn it successfully all the way around. I did remove the tensioner from the passenger side of the motor. At this time I was able to get the cam and engine both set to TDC and got the timing chain back on the sprocket and attached to the Cam. Now the last dilemia I am facing is, when I try to put the tensioner back in there is not enough slack in the chain. I was able to get it all the way back in by tightening the bolts that hold it, but once in place the chain gets so tight that the motor will not turn. After I once again took the tensioner back out, the motor tuned freely. Does anyone else have any further suggestions? I called a local repair shop and they wanted $500 for me to bring it in and have them install a new chain and put the rest of the motor back together? Is this price a little too high? I have seen posts on other sites where most people seem to be paying $300 - $350 to get the same thing done. Thanks for all the help so far, I really appreciate it!

now that u have gotton this far, u should go all the way !!!
hook the new chain on to the end of the old one and get a friend to help feed the new chain around as u slowly turn the engine clockwise.
When the end of the new one comes up buckle it up while it is on the gear .
As for the tight tensioner , take it apart (it is just a piston on the end of a spring) dump the oil out of it . make sure the piston slides freely in the bore, then when u reinstall it should let the motor turn (with a wench on the crank)
you have accually done great so far you just dont know it.

I have checked out the tensioner and it appears to be in good working order. When I install it back into the motor, it is compressed all the way down and the chain is super tight on that side of the cam sprocket. Is there any way to get a little more slack out of the chain, or is it possible that there still could be a kink further down? Not sure how there could be since I have turned the motor over by hand 2 full turns. Thanks again!

if you can turn the motor over 2 turns with no locking or binding , that sounds as if it is working properly
I would say it is unusual for the chain to be that tight without the tensioner installed.
But if you are sure that you have the right top gear and the right chain and it is timmed correctly I would put it together and listen for an awful noise while cranking.

The chain leaves the top gear to the right and goes down through the guide and is fed around the the injector pump drive gear through another guide then around the crankshaft , across the tensionning rail back to the top gear .

There is really no place for a kink to be without binding, if the parts are correct I think you are fine.

I still seem to be having no luck with this pain in the butt! :) This is where I am right now. I bought a new tensioner, the old one snapped in half, and when I install it the chain continues to get super tight. What I think I have figured out at this point is there is some slack in the chain at some point. I removed the oild pump to see the crank sprocket and saw a little slack there, got that out, but still no go. When I line the cam and engine at TDC and turn the motor over 4 or 5 times and then check the timing, it is off. The other thing I notice is when I turn the motor over, the chain gets loose and then tight. Should it have the same amount of tension the entire time it goes around? Is there any way to see where the slack could be and how would I get it out? Thanks!

-Brian



if you can turn the motor over 2 turns with no locking or binding , that sounds as if it is working properly
I would say it is unusual for the chain to be that tight without the tensioner installed.
But if you are sure that you have the right top gear and the right chain and it is timmed correctly I would put it together and listen for an awful noise while cranking.

The chain leaves the top gear to the right and goes down through the guide and is fed around the the injector pump drive gear through another guide then around the crankshaft , across the tensionning rail back to the top gear .

There is really no place for a kink to be without binding, if the parts are correct I think you are fine.

:eek7: OUCH !!! friend after that being said (about the timming being off AND the chain being super tight) it sounds to me as if the top timming gear has 1 (one) too many teeth on it and I believe you could have the wrong gear. Try holding it back to back with the old gear and see if they are the same diameter with the same number of teeth. If they are not EXACTLY the same the new one will not work.

as for the intermittent slack, I believe this can only mean the injector pump drive gear is or the top gear is no longer running concentric meaning something is bent maby the fuel pump drive shaft or somehow the end of the camshaft itself although it would be a feat only king kong could do.
It is hard for me to isolate this problem when I am not looking at the situation, I am glad to continue TRYing to help all that i can!!!

No, I did not replace any of the gears, or the chain. I replaced the chain tensioner that pushes on the guide rail. As for any parts that are bent, I do not see how they could be, as I have not put excessive force on anything. This whole thing is just starting to irritate me more each day! hehe. If there are any other suggestions from anyone else, please let me know. Thank you.

-Brian

The new head gasket thicker than the old by very much ?

The new head gasket thicker than the old by very much ?

The old one was just the slightest bit thinner, which I believe was from being on the vehicle for so long. We Are talking a difference of maybe a sheet or 2 of paper in thickness difference. I did have another thought that I am going to try tonight and see if it works. I seem to keep getting some slack at the crank sprocket and I think I have devised a way to get the slack to the top. I'll keep you posted! :) Thanks!

So what did you eventually find? and what do you think caused it? I'm about to pull the head off a 300TD motor and want to try not to do what you did ;)

I ended up figuring out that I did not have the tensioner set correctly. What I thought was that the tensioner moved in and out on the spring and in actuality it only moves out and locks. I had to take the plunger all the way out and feed it back through the backside after I got the timing chain all re-connected and everything was fine.

awsome dude !!! way to hang in there man :)