Mercedes-Benz Forum banner

Cam shaft adjuster sound

10K views 27 replies 5 participants last post by  Patman1 
#1 · (Edited)
Hi guys,

My cam shaft adjuster is leaking from the connector as many of these are known to. I have not replaced it but in the last few months I have been hearing a rattle sound come from inside this unit.

I don't know how the adjuster works. Could the magnets have broken up and is being thrown around in there? The sound is like 2 small marbles being knocked around in there.

What could it be?
 
#2 ·
If the magnet itself is leaking, you just need to reseal it. If it's leaking out of the connector, you will need to replace the magnet and also seal it. To seal it, you need some engine grade silicone, and you need to put a thin line of the stuff around the magnet and bolt holes. If something is making noises in there, it's the camshaft sprocket itself. You will need to replace the camshaft sprocket and your magnet in this case. Replacing the magnet is straightforward, replacing the sprocket is a little more involved. You will have to remove and reset the chain tensionner, otherwise you will snap the intake camshaft. The valve cover will have to be removed obviously, for this, so buy a new gasket for the valve cover aswell. If your oil cap is leaking, since you're already replacing all the gaskets, replace the oil cap gasket aswell.

Obviously, make sure it's the sprocket, a bunch of stuff in there might to do similar sounds if they are faulty. In particular I'm thinking of the valve lifters and belt tensioner shock.

Also, if the magnet wouldn't work you'd get a check engine light.
 
#4 ·
It might help you to isolate the noise i you chock the wheels/put the parking brake on and leave your car in drive. If it sounds like it's coming from the engine, you can get a mechanic's stethoscope to pin point the noise, it's a really cheap tool, and probably worth having.
 
#5 ·
I used a long screw driver as a stethoscope and isolated the sound to camshaft adjuster housing. But I am not sure if the sound is being passed on to the camshaft adjuster from inside the engine.

The belt tensioner itself sounds fine. Where is the belt tensioner shock please? The front of the 280 is tighter than my ass with very little space to see anything.
 
#6 ·
The belt tensioner shock is a little bit hidden. Look behind the tensioner pulley, you should see a small shock looking thing. One end attaches near the thermostat, the other end attaches at the tensioner. It is possible you don't have a shock, a few cars had a different tensioner that didn't have a shock.
 
#8 ·
The tensioner itself is indeed its own unit. But think of it as a spring-loaded lever that maintains the tension on the pulley. Any sprung system could vibrate for whatever reason, and once springs start vibrating, typically it will take them a while to stop on their own. This could cause additional wear on the belt, and possibly to the pulleys themselves. The shock is there for the same reason a car's suspension has shock absorbers, to dissipate the energy stored in the springs. So the little shock actually dampens the motion of the tensioner pulley.
 
#9 ·
tensioner shock

The timing belt tensioner on these cars is what I call an "elegant" design. By that I mean a fancy solution that goes way beyond function. They use the tension of rubber between two cylinders to provide for tension of the belt. Some applications like my old 500SL use the natural hysteresis of the rubber to provide damping. The C280 uses an oil filled shock for the damping. Now the elegant part. Sorry, but to use rubber to do the same function as a steel spring is just plain nuts. In an area of elevated (210 deg) temperature rubber is the wrong material. Steel springs will outlast the engine!
 
#10 ·
The timing belt tensioner on these cars is what I call an "elegant" design. By that I mean a fancy solution that goes way beyond function. They use the tension of rubber between two cylinders to provide for tension of the belt. Some applications like my old 500SL use the natural hysteresis of the rubber to provide damping. The C280 uses an oil filled shock for the damping. Now the elegant part. Sorry, but to use rubber to do the same function as a steel spring is just plain nuts. In an area of elevated (210 deg) temperature rubber is the wrong material. Steel springs will outlast the engine!
That makes no sense. The tensionner has a steel spring. The only rubber in this system that functionally acts on the belt's tension is the bushing on the end of the shock. Steel springs also certainly will not outlast an engine. Think about all the cracked coil springs that happened long before the engine had any trouble. Engines are probably the most durable part of a car. Following your logic, suspensions shouldn't use rubber bushings because metal bushings will last longer. Sure I guess, but then the ride would be EXTREMELY harsh. Rubber is an excellent material, and just like every other material, it has its uses and it has its limitations. Cars don't last for ever without some maintenance.
 
#11 · (Edited)
"That makes no sense" is a profound and unfortunate statement. In the spirit of the Christmas season, I will be kind.

I owned a 1990 500SL and had the failed serpentine belt tensioner in my hand! If you look carefully you will see a black circle around the bolt that is indeed rubber molded between the bolt and the body of the tensioner. There is 12 mm cap bolt that bolts the tensioner to the block. A long tension bolt goes thru a slot with a nut to turn to provide the tension. With the cap bolt loosened, the tension bolt is tightened until the proper tension on the belt is achieved and then the cap bolt is tightened. Sorry, but the tension on the belt comes from the rubber, no steel spring! The SL had no shock!

I also have a 1994 C280 like the one that is the subject of this post. I also had the failed belt tensioner in my hand and it was of the same design. Like the SL, the tensioner had no function as the rubber had cracked all around, and separated from the body of the tensioner. Note that this design does have a shock absorber and the recommendation is to replace the shock along with the tensioner. (Note that after engine # 12-034966 the tensioner has a different part # and it probably uses a steel spring and does not use a shock.)

Back to the "elegant design" comment. As an engineer myself I think I am entitled! Note that MB did use a tensioner design using rubber as the spring, and later updated to a simpler steel spring. Later SL 500's also used a steel spring although I have not inspected that part myself.

Here are images of the two tensioners and the tension bolt





 
#12 ·
Actually now that makes more sense. I was convinced you were talking about the shock for some reason. Anyway, I didn't know there was a rubber tensioner (I knew there were different kinds of tensioners, but not that one of them was made of rubber). In this case it does seem silly to have rubber act in place of a metal spring, especially given the proximity to the engine. The steel tensioners rarely fail, and the source of clatter on initial startup can be caused by just a bad shock (in particular, the rubber bushing at the top end of it).
 
#13 ·
I think they added the shock for the C280 to minimize failure of the rubber due to repetiitive flexing. Again my comment about elegant design where a spring is the simple solution. I know that each time the AC compressor cycles, there is a spike in the load on the belt so that may be why they use the shock!
 
#15 ·
This was the old style tensioner typically found on W124 cars and the old M104 engine. An OEM tensioner was higher quality and had a decent service life but the market now is all knockoffs and quality is poor. If you maintain one of these older cars you get plenty of practice changing the tensioner. And it was a Rube Goldberg concoction with the tensioner, adjusting bolt, little plastic indicator gauge compared to a single piece steel spring tensioner. After owing a few iterations of MB you appreciate some of the advancements that the engineers have made. This being one of them. The difference is like night and day when changing a water pump on a M112 engine versus on the older M104 engine.

And just for the record we are talking about the serpentine belt tensioner, not the timing belt tensioner which is a whole different thing.
 
#16 ·
By timing belt you mean timing chain? :D

Yes we are talking about the accessory belt tensioner. I'm curious to which one I have now, I have a shock, but from what I gather I have the steel spring one. I'm guessing they kept the shock to dissipate any oscillations in the belt, rather than leave that up to the belt itself and possibly have it wear quicker.
 
#17 · (Edited)
Yes, timing chain. Post #9 introduced timing belt when we were all talking about the serpentine belt.

You probably have the newer one piece tensioner (good!). The pics show the older 2 piece affair with the tensioner and adjusting rod.

Adjusting the older tensioner was a pretty silly process.

The first pic is a pretty good pic.

Just to the right of the tab on the left of the housing is a little embossed "ramp". The procedure being, get it assembled with the adjusting rod, put the plastic pointer at the beginning of the ramp. Tighten the adjusting rod, thereby moving the arm with the pulley to apply tension to the belt, tighten until the pointer moves to the top of the ramp. Then lock the tensioner into position with the center bolt.
 
#18 ·
I took time today and decided to listen and see where the sound was coming from. I used a stethoscope and the loudest sound comes from dead front, dead center, right around the cam shaft sensor/adjuster location. I have not looked for the shock so I will do that tomorrow. The tensioner, alternator, water pump are all quiet. I am afraid that Patman is unfortunate for me sounding quite correct. It is the timing chain itself or likely the chain tensioners gone bad and is letting the chain slap around.

SO, how long before my engine dies? I don't have the know-how to fix this myself and don't think I want to pay a shop to do this as it seems like an expensive problem to fix.
 
#19 ·
I'm wondering if you could pull the timing chain tensioner out, reset it, and reinstall it?


That would be a simpler process, but may or may not fix it. There could be an issue with the chain that you don't know about. If done properly, it's certainly not going to hurt anything.
 
#20 ·
#22 ·
Don't jump to conclusions just yet. The usual suspect is the intake camshaft sprocket. The chain tensioner and the chain itself are very robust, I wouldn't worry about those failing. For now, let's assume the sprocket is bad (it probably would make a sound coming from right in front, seeing as the magnet may pick up some noise and make it sound like its coming from the very front). Replacing it is not a dramatically huge deal, remove the valve cover, take the chain off the intake sprocket, replace with a new sprocket and work your way backwards. There is one kink in the operation, your chain MIGHT not have a master link, which could make it annoying to remove. Before reinstalling the chain though, you MUST remove the chain tensioner and reset it. You car does have an automatic chain tensioner, however, it's a little bit different due to how chains stretch over time. Think of it as a "ratcheting" mechanism. Once it clicks forward one notch, it won't go back on its own. What's going to happen is: you will remove the chain from sprocket, so obviously, there will be a lot of slack in the chain, so the tensioner will try to eat all of it up (it's spring loaded), and will go to full tension. Unless your engine has a million KM on it, the chain will not need to be in full tension. If you install the chain like that, when you turn the engine over, there will be so much bending force on the intake camshaft that it will snap at the sprocket end. If you've ever seen those threads like "oh no, my intake camshaft has snapped and wrecked my engine, what do I do?" I promise you the reason it happened is because the person did not reset the tensioner. Resetting it takes about 30 seconds, you remove it, you open it up, you put it back together, pushing the internal pin 1 click only, if you felt 2 clicks you are already too far, and you put it back in.

Anyway, assuming the tensioner is bad, or the chain is too stretched (an outcome which would be really surprising), it still isn't a terrible bother. Zip-tie a new chain to the old one, rotate the crank until you've got the new chain all the way through, reset the tensioner (or replace it with a new one), and if you aced it you won't even need to adjust the timing.

M104/M111 engines are just a joy to work with.
 
#25 ·
Found the issue. Took off the front coolant hose, wires around the cam sensor etc...and sure enough behind that forest the issue was plain as day.

The top of the tensioner shock with the bolt was rattling like crazy. The bushing was completely gone.

I will try placing a small piece of fuel tube in there as a bushing but not till the spring. Is this a problem if I let it go longer? what can happen?
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top