Main.TrailIndexPage | Engine | Timing Chain

Timing Chain

This component is part of Engine.


Define the component. Include, if known, the german language word for the component, as well as the English or American equivalent. Show a picture, a diagram.

  • Its technical name & common name(s)
  • part # - start year & end year
  • which area it belongs to - engine, transmission, body, injection etc, link back to the relevant section


Describe, in general terms the function of this component. Meaning what is it there for and what role it plays. Describe how it works, the inside mechanism. Use diagrams to explain.


Describe common maintenance procedures, and common faults that may occur. Describe how these may be diagnosed and resolved. Again, include diagrams, photographs and explanations. Where possible, include measures, tolerances, weights etc.

Timing Chain Tensioner

The chain tensioner on the W113 engines is a mechanical/hydraulic unit. It is mounted directly below the thermostat housing. A piston protrudes into an oil pool in the chain gallery of the head, where it contacts the chain tensioning sprocket arm.

An opening in the end of the piston draws oil into the hydraulic cylinder and a check valve prevents the oil from escaping. Normal engine operation and chain sprocket movements provide a pumping action which keeps the tensioner and chain tight by filling the piston and housing with engine oil.

A spring inside the tensioner provides some tension, however the real work is done by the hydraulic pressure. This spring is also critical in the operation of the oil check valve of the tensioner. This check valve involves the ball, the cap and the spring.

A plastic or metal spacer is located in the tensioner spring and limits inward travel of the piston.

The "oil pool" is an area built into the chain gallery of the head which collects oil as it splashes inside the engine. The opening in the chain tensioner piston retrieves oil from this "oil pool". A 6mm socket head bolt is also located in this oil pool. This bolt must be in place or a severe exterior engine oil leak can result. The threaded hole for this bolt can emerge on the exterior of the block behind the water pump. If the bolt is left our during repairs, a mysterious oil leak may result.

The chain tensioner provides chain tension until the chain wears or stretches beyond the tensioners outer limit at which point the timing chain would need replacement. These tensioners are very reliable and durable and normally last the life of the engine. There are no seals invoved in the hydraulics. Very, very tight tolereance between the piston and its housing (cylinder) insure good seal and long life. Instances of tensioner failure on these engines is very rare.

An aluminum seal is located uder the "cap". Also large rubber "O" ring is seated in a groove at the tensioner/head parting surface. These two seals prevent oil from leaking but are not involved in the tensioner hydraulics.

Removal of the chain tensioner is accomplished by removing the thermostat housing and removal of the two nuts at the tensioner. If the car has factory AC the complex compressor brakcet must be removed. It is not necessary to remove the chain tensioner sprocket and arm in the chain gallery when removing the tensioner.

  • How to replace your timing chain (although it's for a diesel, the procedure is the same). Dan Caron says: timing chain replacement is easier than it sounds. Put the engine to TDC number one piston. Remove the chain tensioner, you will need to take the thermostat housing off first. If there's a master link on the chain look for that first if not grind off two pins on the same link. Put a rag around the chain case opening because you WILL drop something in there if you don't. Using the new master link attach the old and new chains together. Slowly feed the new chain in until it comes out the other end and then undo the master link and throw the old chain away. I usually wire the chain to the camshaft while I'm taking the master on or off. The chain can slip off and fall way down it there. Replace the master and turn the engine over by hand a few times to make sure you have it in time. Replace the chain tensioner. I usually put a new one in if the chain is really worn. Bleed the tensioner and put everything back together. You may have to re-time the ignition.
  • Symptoms when it faults
  • How to test if it is faulty - what tools to use
  • How to fix / change

Link to related components where appropriate.

Old Yahoo content

The following is the content from the old Yahoo documents on the site. It needs to be structured and edited in the correct sections of the entire document. After moving particular content to its correct place in the manual, please delete it here.

I was just checking my M 130 engine which is awaiting reinstallation into the car and noticed that the crankshaft/camshaft alignment is correct at TDC, but that the distributor was off by about 30 degrees (outside of the range of adjustment of the distributor). Now, since neither the distributor nor the camshaft had been removed after the engine was pulled out, I realized that the clicking sound that came from the engine when I rotated it clockwise one time must have been the timing chain skipping over the gear on the intermediate shaft, which drives the distributor and the fuel injection pump. I read somewhere that you are not supposed to turn the engine clockwise and I assume it is because the chain tensioner is not as effective in that direction. The only thing that puzzles me is how the intermediate shaft's gear could skip, seeing that it offers little resistance from the distributor and the fuel pump when the crankshaft is turned. In order to correct the problem without disassembling the fuel injection pump and intermediate shaft, I removed the idler shaft and gear as well as the chain tensioner, in order to give the timing chain enough slack, so that I could rotate the distributor (and thereby the intermediate shaft) back onto their marks. Can anyone shed any more light onto this question? It seems like everything is checking out fine, but I wouldn't mind raising my confidence level more in case my reasoning is incorrect. I haven't looked into the timing of the fuel injection pump yet, again, assuming that this was corrected when I readjusted the intermediate shaft.

Frank says: check the spark plug wires at the old distributor cap. Chances are, at some point in the car's life, the distributor was removed and then replaced incorrectly. Sometimes instead of fixing it correctly, the mechanic will "cure" the problem by shifting the position of the wires in the cap.

Will says: I hesitate to wade into this one, but will do the best I can. As Frank suggested, perhaps the wires were swapped. This led to the timing being off. You have some other things going on as well, I suspect. You can turn the engine which ever way you want to. Nothing will fall off or mess up. The tensioner works either direction. There just is not much reason to turn the engine backwards. Frontwards or direction of rotation for the engine is clockwise as seen from the front of the engine. If you use a socket on the crankshaft bolt and are trying to tighten the bolt, that is the direction of rotation. The bolt is in very tight so if you do rotate the engine backwards, the bolt will not undo. If all the sprockets and chain are correct and the tensioner is applying even moderate pressure, there should be no way the chain will come off a procket and skip 2 teeth. The 30 degrees you mention is worth about 1 /2-2 teeth of the chain or a sprocket. There should not have been a clicking noise unless something is loose. Perhaps I can give you an idea of what it takes to make the chain jump a tooth. If the chain is stretched and worn, if the sprockets are worn, if the tensioner is collapsed, the chain will still not come off completely. What will happen when the engine is running is the chain starts to ride off the camshaft sprocket and hit the inside of the cam cover. Soon you will hear the chain grinding the inside of the cam cover. But, the chain will still not come off or jump time. The easiest fix to what you described is to make sure the crank is at TDC, the cam is on its mark, and as the final check, both lobes of the cam for #1 piston are pointed up. That means both valves are closed. Then remove the distributor, use a long 5mm bolt and screw it into the shaft below the distributor, pull out the shaft, rotate and re-install it, re-install the distributor, and check to see if the rotor is pointing to the hash mark on the rim of the distributor housing. Then check if you have proper range of motion for adjusting the distributor. This may take several attempts. Note the drive for the distributor is offset.

I just went through this a couple months ago - many times. the Haynes manual is pretty clear but says the distribuor should be at 45 degrees and shows a picture. That is correct. They do not tell about both cam lobs pointing up - that is good to know. I don't think the chain can jump. Look for another reason for the noise. If you can re-install the fuel injection pump, your mind will be at ease.

I went to check the cheat fix that Frank mentioned with the spark plug wires (I actually thought that was quite inventive for a quick and dirty fix) and found that they line up the way they are supposed to, i.e. no. 1 wire at the mark on the distributor edge. Seeing as everything else lines up with TDC after I moved the intermediate shaft over by two or three teeth, I still have to assume that the gear had skipped over when I turned it in reverse (Will, I meant clockwise as seen from the point of view of the engine, looking forward.) The engine was running fine when I removed it from the car and I hadn't taken any engine parts off except for pulleys, lines and other peripheral parts. Also keep in mind that the engine had been sitting without oil pressure for several months so that the chain tensioner may have been drained of oil and that the chain has a lot of slack on the side of the auxiliary shaft when the engine is turned in reverse. Will, if you can believe it I once rebuilt the cylinder head on a BMW 3.0 inline 6 including milling about 0.5mm off the surface of the head. I reassembled the engine, started it and had a loud clatter come from the engine. Upon a second disassembly I found that the camshaft timing was off by a tooth even though I was quite certain that I had set it correctly (by the way, the clatter was from the valves just barely interfering with the pistons and making contact). Anyway, I had to go through the process of resetting the timing twice before I realized that the combination of timing chain stretch and milling the head had created enough slack to repeatedly cause the chain to skip over the camshaft gear. I still have one more concern: like all of you, it is still not quite easy for me to believe that the chain skipped over the intermediate shaft gear on my M130E engine. So, in the event that my remedy was incorrect and I now have an engine where the camshaft and ignition timing are correct, but the fuel injection timing is now off by the amount that I corrected for on the intermediate shaft, can this cause any damage to my fuel injection pump upon starting the engine up? How easy is it to simply unbolt the fuel injection pump for a quick check to verify that its marks are aligned as well? If I do this, the pump doesn't go out of adjustment, does it?

Frank then says: that's a good point about correcting both the ignition and injection pump timing after having the head milled. Removing the injection pump isn't too bad a job, provided the cap nuts come loose OK. Be sure to use the correct mark for timing the pump. If after setting the cam timing the valves still hit the pistons, it's a sign that the valve seats weren't deepened as they should have been when the head was machined.

I took the fuel injection pump off and sure enough it was off by the amount that I had compensated for on the intermediate shaft. I guess that means that the distributor gear may have skipped on its own, even though the distributor had never been loosened. Go figure.

Frank then: I trust you followed the instructions when re-timing the pump, and used the 20 degree injection timing mark instead of TDC.

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