miss/rough idle problem identified
 

i decided to give up and take my car somewhere for diagnosis. 15-19 degrees of chain stretch. the tech was nice enough to take me back and with the help of another guy showed me the pointer on the crank and how at zero moving it backwards didn't start moving the cam sproket until about 16 degrees.

any good sources for write ups on this repair?

also, what's a good price to expect to pay? they charge $103 an hour.

Whoa never ever never ever turn the crank backwards :eek:

This is probably why you are showing 16* out of time...the chain is at great risk for jumping a tooth if the engine is rotated backwards (counter clockwise). I would not start the engine without verifying by hand (going forward=clockwise) that you do not have valve to piston contact.

I would reach out to (local to Charlotte) forum member vstech before going further.

I'm still learning a lot about this engine but... i find that just a little bit hard to believe.

You may have some thing like what was going on in the first post of this thread.
http://www.peachparts.com/shopforum/diesel-discussion/321819-om602-timing-chain-stretch.html

You can never ever jump a teeth by turning engine counter clockwise. It is physically not possible with a OM60x engine.

any chance adjusting the tensioner will cure the problem?

The tech is using the wrong procedure, and I would not have any further confidence in that shop.

See this thread, my post #6, for a procedure from MB. This will give you a rough measurement. Fine measurement requires using a dial indicator and really do you need to know if the stretch is ~5 degrees or exactly 5.23 degrees? Rough method is close enough.

http://www.peachparts.com/shopforum/diesel-discussion/203770-timing-chain.html

You can get a little more accuracy by lining up a straight edge along all the marks on all the cam towers, and letting the end of the straight edge fall directly over the cam gear shoulder.

No, it is not adjustable. If it has failed, replacing it will certainly help!

I agree with...
 

Maxbumpo on the mechanic using the wrong procedure and to not have confidence in that mechanic.

Without oil pressure (not running) the tensioner will have a little play, they have a course ratchet kinda mechanism that always pushes the tensioner rail tighter against the chain as stuff wears out. And then when running, oil pressure keeps it in constant tension.
When turning the crank back and forth with a socket it will make the tensioner move in and out a little thus causing the cam to appear not to move.
Turning it backwards WILL put extra unwanted load on the ratchet mechanism, but it wont break anything or jump teeth or do any catastrophic damage.

That "mechanic" is an idiot. Go somewhere else for sure!!!!

x5 - measure chain stretch properly then report back. The eyeball method is good enough to get you started. I don't think you can turn a 60x crank 20* independently of the cam/s and not have valves hit pistons. The tensioner isn't a factor when turning the crank clockwise by hand. The crank pulls the chain over the IP and cam. There's no slack in those spans when you turn clockwise. The slack between the cam and crank can flap away without affecting valve timing. The dynamic of an engine running on its own changes things considerably.

Here are some pictures of actual engines to help you eyeball cam timing - http://www.peachparts.com/shopforum/diesel-discussion/349556-timing-chain-stretch-1987-300sdl.html

Rolling in a new chain isn't rocket science but there is some art. Guidance for a 616/7 engine is 95% of what you need for a 601/2/3. If the chain is stretched beyond spec, certainly if to the tune of double digits, replace the cam sprocket as well.

Sixto
MB-less

Holy cow thanks for all the informative responses! The pics of viewing the marks through the front of the cam sprocket makes sense now. I'm gonna pull the valve cover myself and rotate the engine and check the crank pointer. Just to clairfy, the engines correct direction of rotion is clockwise facing the front of the car?

Rotate via crank bolt until the timing marks viewed THROUGH the cam sprocket are lined up and then check where the crank pointer is?

Sounds like he measured the available slack in the chain system. The slack for all practical purposes is of little to no concern. It has to have some.

Hard for me to believe with overhead cams being around as long as they have someone could make this error.

What is really bothersome is a guy being able to charge 100 dollars per hour with so little ability and knowledge.

ok, today when i got home from work and pulled the valve cover and turned the engine by hand. i lined up the timing marks through the cam sprocket and looked at the crank pointer. not good.

had i bothered to clean the sludge off the pointer you could see exactly how far stretched it its, but its safe to say it's somewhere between 7 and 8 degrees. dammit.

i would def. agree about the comments about this mechanic/shop and $103
per hr they should know this stuff.

still need to find a place around CLT that has a good reputation and knows our cars.

I wouldn't jump at changing the timing chain from that single data point. It is hard to get accurate measurements using the timing marks. A better method is to measure valve motion with a dial indicator to find the true camshaft clocking, but that does take more time. Even if you had 8 deg stretch, I wouldn't jump into a chain replacement. Delayed valve timing gives more power at high rpm, at least in gas engines, but air flow into cylinders is the same phenomenon in a diesel. Racers purposely delay their valve timing for more power. If still worried, there are offset key-ways you can put on the cam gear to correct. I can't imagine 8 deg of lag causing a rough idle. BTW, the way the shop measured your timing slop is correct for a 60's push-rod engine like a Chevy 350 or my old Mopars, but not applicable to OHC's which have chain (or belt) tensioners.

For a rough idle and miss I really would not consider checking the chain stretch early in the game. Why not tell the members what you have already tried with the problem? There are many things that you can manage with a little help from members.

I do not think many if any will suspect the timing chain is doing this.
Seven or eight degrees off if true should be corrected as part of a tune up though. Even if you decide on a new chain the money should not be spent until the real issue is found.