Cam timing mystery may be over
 

A little while ago I posted complaints about altered performance and strange noises after having my timing chain replaced in my 76 300D.
Finally after gathering information from this site and having the car looked at by a couple of mechanics, I may have found that the cam gear is off by one tooth. I had asked about cam timing before and the mechanic that did the job checked it and said it was 2 degrees advanced. I don't know what method he used but based on the knowledge of the people who have tried to help out on this site, I lined up the marks on the cam gear and bearing tower and read the marks on the balancer to my amazement finding them to read about 15 degrees BTDC.
I checked several times and made sure there was no slack in the chain on the side opposite the tensioner rail. The readings were about 14, 15 and 19. Apparently, one tooth alters the degrees by about 10 or 12.
Now, I think back and remember when the mechanic checked to see if we had missed a tooth (I watched to whole process) he didn't use this technique and I see where he went wrong. This is strange because he is a very good mechanic and has an excellent reputation.
But THANKS to this site and the people on it I think I have saved myself from chasing Ghosts in my engine. Not to mention spending loads of money replacing fine parts IE Cam.
So, now I'm wondering what kind of damage has been done to my valves. It's been about 2000 miles since the job. It's amazing that it has run as well as it has, but there has been a distinctive metallic clacking sound ever since then and I've had no mechanic think much of it. Now I know that was probably a valve contacting the piston ever so slightly. Thanks to the fact that I just had the valves adjusted prior to the chain job and that they were right on spec probably saved them further damage.
If indeed, the cam is one tooth off and the valves have hit the pistons, what does this mechanic owe me beyond fixing the cam timing for no cost? A complete Valve job?
I'm having another mechanic verify the cam timing before I go to this guy and point some fingers.
Well at any rate, I appreciate this site greatly and the help I've gained from it.
Thanks
Josh

JOe,

Your on the edge it sounds like. it's hard to say "how much damage". You need to remedy the situation and then see how she runs. There maybe zero damage......




Michael

In reading your write up I was unable to ascertain whether you corrected the timing or not? Have you? How is the car running now? If it is running good - relatively smooth idle, no smoke, starts easily, etc... then I would leave it alone.

I have attached a pic of the #1 piston out of my 300D where the car was run with one tooth off on the chain (19 degrees). This engine had been run at 100+ mph with the timing off. The #3 piston looked the worst. This was the only visible damage and I will eventually get around to rebuilding this engine. My machine shop is telling me to replace the exhaust valves too. For right now I just picked another engine up off of ebay.

Disregard the oil on the top of the piston. I had spilled a little on it when I pulled the head off. The only damage is where the exh valve hit the piston.

Doubt you'll get very far with the mechanic.....

I knew someone whom the dealer put gas in his 1999 diesel, he battled all the way up MBUSA about possible longterm injector and pump problems. They finally gave him a free starmark out to 100,000 miles.
Most shops do very little-even when it is obvoiusly their fault.


Michael

No I haven't corrected it yet. Fortunately I have something to drive in the meantime.

engatwork, I don't understand the notion of not correcting it. Clearly the vavles have been hitting the pistons and I've been hearing this all along and my mechanics haven't given a !@#$.
It runs amazingly well considering.
How long did you drive the car with the timing off and how loud was the tapping noise? Based on your pictures it would seem that smooth combustion would be affected and the valves probably wouldn't seat properly after that trauma. Assuming I'm not going to rebuild my engine and that I'm not going to get a complimentary valve job, I'll have to hope it wasn't damaged too badly.
I don't understand, my mechanic is a nice guy and a really good mechanic, guess he was just having a bad day. Or I'm just a sucker. . .
I would think at least he'd set the timing correctly for no charge.
samiam, thanks for your help. Do you remember when I posted way back when about this subject?

sorry Josh - I meant to say - put the timing back right and if it runs good, smooth, no smoke, etc... then leave it alone. It is pretty easy to put back right.
I drove mine for about 3k miles with the timing one tooth off and all my mechanic did was go to the frigerator and get another beer (my mechanic is me).

LOL engatwork!

Jim, You keep your machinist tools in that refrigerator right next to the beer , right ? :D

Josh

I think I have the instructions for moving your chain one tooth if no one comes up with it. Sounds like you can slack the tensioner and get enough slack in the chain to sort of "bunch" it up and work it over the sprocket. I have never done it but saved the post for future use. Let me know if you need it. Good luck

I did not realize he was asking how to move it over one tooth. It is easy and just like you say. Back out the tensioner, unbolt the cam sprocket and slide it out enough to move it over one tooth. Then move the camshaft to line up the keyway, slide the sprocket back on, install the fastener (torque to spec) and tensioner and you should be good to go. Should not take more than about an hour.

engatwork

I'm not sure he was asking about how to do it but he might want to start doing his own work after an experience like that with a "good" mechanic, who knows what a lousy mechanic might have done :( The method I was talking about does not evolve removing the sprocket but since I have not done it i really don't know for sure, just an idea. Either way should not be a big deal. i find it odd that the guy didn't check the marks before putting the valve cover back and collecting his cashola.

FYI:
The MB manuel for the W123 says that off a tooth will be 18 deg. Having been there and done that I can tell you that the chain can very easily be moved over one tooth by loosening the tensioner and bunching the chain along the top of the cam gear. You should clamp one end to keep track of where it started.
I had the chain off a tooth and drove it about 1200 miles. Have not pulled the head, but it may have bent one of the valves a bit. Can hear a little wind blowing into the intake when compressed air is blown into the cylinder.

I was wondering if it would be possible to bunch the chain up and move it over one tooth. I wouldn't want to unbolt the sprocket and risk dropping the chain, I'm not that proficient a mechanic to deal with that. Thanks for the advice.
I think the mechanic should fix this for free. Of course one wonders about having him touch the car at all.
I remember, after he installed the chain he positioned the crank at TDC using the marks on the balancer and looked at the marks on the cam tower to see if he missed a tooth. I was there at the time and thought it was odd that they didn't line up exactly, but I didn't know any better. I think he underestimated the amount of degrees the engine moves in relation to how much the cam moves and he must of thought that everything was set correctly. This is all speculation though. I'm going to have another mechanic look it over and then I'm going to pay a visit to the other one.

Conclusion!
 

Well, indeed it was off a tooth. Not to mention the cam gear was reversed. My mechanic (not the one that did the work) helped me set everything right and wasn't even going to charge me. I insisted, so he charged me half and hour.
The car runs and sounds like it's old self again. I dont think anything was damaged internally. The only thing that sucks is the chain was not straight laterally. Because the cam gear was on backwards, it was pushed further out at the top and may have worn funkily. It's only been a couple thousand miles though and probably isn't too serious. I'm just glad to have my diesel back the way she is supposed to be, smooth and ready to cruise. (sorry for cheesiness)
Thanks to MB shop!
Josh

Whaaat?

The timing gear was on backwards??? That boy has *zero* clue on how to wrap a timing chain in an engine if he removed the cam gear.

For reference, wraping timing chains is EASY!!! Very easy with two people. Take the injectors loose or gp's out. Use a couple wire ties to firmly attach the chain at each end to the gear. Now do the manual thing... grind and remove a link. Use a temporary master link to put in your new chain. Then tie something to the backside end of the old chain. Now with your helper holding both firmly(new chain is important). Cut the ties, and gently turn the engine over by the crankshaft.
I start this whole proceedure at TDC. Then, you need to put the permant master link in the chain. I put zipties on again(wire ties), so the chain cannot jump time. You can also remove the timing chain tensioner before doing this(??). Anyway, the wire ties prevent the chain from jumping or dropping into the crankcase.
There is NO way an attentive person cannot hear, feel and see the chain jumping a tooth!

Not finding the mistake doesn't suprise me. Most mechanics only feedback is repeat customers. All repeat customers *love* the work or they would not return. Hence, most have *huge* heads or egos... mine has since been removed by NASA soon after graduation.

Michael