timing chain replacement questions - PeachParts Mercedes-Benz Forum

Maverick · #1 01-28-2002, 03:32 PM

My 603.970 is making that classic “rattle-rattle” at startup and at idle. The noise goes away with increased RPM but I feel it’s time to replace some timing chain parts A couple questions relating to the replacement of those parts:

Can all the timing chain related parts be replaced with only the removal of the tensioner and the valve cover?

If the current timing chain has no master link, can I assume it’s from the factory?

What is it about the tensioner…does it loose its ability to hold oil pressure and thereby loose pressure to the chain rail?

Visually, the chain, cam sprocket and rails look fresh and I’m planning to hand rotate the engine to #1 TDC to check for stretch. If within limits, unless strongly advised otherwise, I plan to replace the tensioner only.

I’ve read quite a few threads re: this subject and they have me pretty well spooked enough to take the car off the road until I address this issue.

Mav

mbdoc · #2 01-28-2002, 05:42 PM

All of the diesel timing chains come with a PRESSED style master link!
YOU should look for 3 or more degrees of chain stretch & then replace it.

JimSmith · #3 01-28-2002, 05:49 PM

Maverick,

I am not familiar with your chain tensioner, so you may disregard this response if you think it does not apply. My 240D chain tensioner has a spring and a cylinder and piston inside. When the engine starts the oil pressure comes up and adds some force to the spring's effort to push the piston to the far end of the cylinder. On the other side of the piston is a little extension that sticks out of the cylinder housing and it pushes against a rail that pushes against the chain, taking up the slack.

I can not figure out how one of these will fail, or why anyone would want to replace it to correct the symptoms of a sloppy chain (even though I did it once on a 220D, but I changed the rail then too - but now that I have seen the old one, and it had >200,000 miles on it, and a new one side by side, and having fiddled around with the old one once it was replaced, there is nothing significant to fail in them). If the little piston inside is at the end of it's stroke, and it cannot maintain the necessary tension, putting another one of the exact same dimensions in there will not cure the problem. Either the chain is stretched so far the tensioner stroke is inadequate, and the chain needs to be replaced, or the rail surfacing is worn down and the rail needs to be replaced. Hope this helps, and somehow applies to your car. Jim

Maverick · #4 01-28-2002, 06:56 PM

Jim,

A representative from The Benz Bin informed me that the piston inside the tensioner looses its ability to hold oil pressure and apply pressure to the rail with wear. I guess the seals go bad and leak down applying less and less pressure. He seemed pretty sure that the chain was not the cause of the noise and only the tensioner needed replacement.

In reading all the threads regarding this subject one gets a different impression. I’m trying to gather as much info as possible as I tend to do all maintenance myself.

Thanks much…

Mav

psfred · #5 01-28-2002, 10:05 PM

Mav:

The 603 uses a ratcheting tensioner -- it is pushed out by oil pressure, but locks in place and does not retract when the engine is off. If the chain is stretched too far, it won't stay out past the last tooth on the ratchet, and could give you the symptoms you describe.

Make sure the ratchet is relieved (plunger all the way into the housing -- I think you have to pull it out and put it back in from the back or something) -- if you manage to get the chain on with the tensioner too tight, it will damage the new chain.

The tensioners do get leaky with age -- the o-rings on the plunger go bad. With the ratchet, though, they shouldn't drop back.

Take a look. I'm sure the tensioner rail can be replaced, along with the one or two at the top. Lower driver's side rails will probably be hard to change with the engine in the car.

You do not want to break the chain on this car, the repair bill would be as much as the car is worth!

Peter

Aaron · #6 01-29-2002, 01:00 AM

As MB DOC said, watch for 3 degrees + of stretch and then replace chain and tensioner! Don't just do it 50%, you'll be happier in the end.

Maverick · #7 01-29-2002, 09:57 AM

Peter,

Since I have a new tensioner on the way, I dissembled the old one this morning. I couldn’t see anything internally that would resemble a ratchet. It looked like its only function was that of oil pressure pressing a plunger out with the help of a spring. Can’t speak to the new tensioner though as I haven’t see it yet.

Checked the timing marks this morning and found the crank to read "zero" What a relief, as I really didn't want to tackle the chain itself. I know that this stretch check is not as accurate as that with a dial caliper but given the result, would you think that the chain rail would need attention? I couldn’t see how one would remove the rail without removing the chain first.

Thanks much…

Mav

psfred · #8 01-29-2002, 07:49 PM

Mav:

Hmmm. I was under the impression that the tensioner in all the newer motors was a ratcheting one, but I could very easily be wrong. If they aren't, it sounds as if you certainly have a bad one.

I've never looked into the 603 -- you will at least have to remove the front cover before you can get the chain guides out.

peter

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