I Installed a New Timing Chain and It "Jumped" Some Sprocket Teeth

Now the timing marks don't line up - What do I do! - Help...

Over the years I have received a number of emails similar to the one that follows. If you are not super careful when installing a new timing chain you can end up with a "Big Wrench Dance." Let me share this email with you. You can read this email at the very bottom of this text. This can be "fixed" but if you feel you are in way over your head I recommend you seek help from someone experienced in dealing with these types of major engine work. Below you can read the following steps I recommend for fixing an "engine out-of-timing situation:

Problem & Solution

Common among these chassis:

W110 W111 W112 Sedan
W111 W112 Coupe
W108 W109

1. Begin by turning the engine over clockwise until you have number one cylinder coming up on compression stroke and align the timing marks on the front of the engine to be set at top dead center ( 0 or TDC)

2. Now, look at the cam or camshaft marks to see how many teeth they are off and which way you will need to turn the sprocket to get the marks lined up again.

3. Next, you have to remove the rocker arms for the camshaft you are going to move. You do not want any valve spring pressure fighting against you when you go to turn the camshaft.

4. Now you will have to remove the bolt on the front of the camshaft in preparation for pulling the sprocket away from the camshaft. On diesel engines, you may have to remove the upper chain guide rail.

5. Cover the hole with rags below the cam sprocket to prevent anything from falling down in the engine.

6. With the chain on the sprocket pull the sprocket off the end of the camshaft and do NOT let it drop nor let the chain move away from the teeth. If you do not have enough slack to pull the sprocket off the cam you will have to remove the chain tensioner.  

7. While holding the chain tight with the sprocket ( I recommend a helper here) get and a big pair of pliers and rotate the cam until the cam marks line up again.

8. Now you will have to carefully lower the sprocket away from the chain and move the sprocket the number of teeth you estimated you were off. This may take a couple tries. When you are sure the cam marks are lined up properly and the sprocket and the keyway on the end of the cam are lined up, you can push the sprocket back onto the cam and tighten the bolt back down.

9. Put the rocker arms back and re-install the tensioner if needed.

10. At this point, you should check the injection pump timing on diesel engines and distributor timing on gas engines to make sure that did not move as well. It is a good idea to do this anyway after installing a new chain because that can affect both injection pump and distributor timing.

I have a short video that just gives an overview of the procedure on the V8 engine. CLICK HERE to watch that video.  I recommend you obtain the factory engine service manual and the Haynes manual for your engine. They can both help with details, torque settings, and related procedures. 

"I recently tried replacing my timing chain on om617 engine. I removed the tensioner, rocker arms, undid the old chain and connected a new chain to it. I had a helper who was holding the old chain tightly while I was turning the crankshaft and feeding in new chain. While I was turning the crankshaft the chain kept skipping teeth and timing got messed up. I don't understand how? Like I was turning it and at first it was going slowly and surely and then all of a sudden the camshaft gear goes clockwise fast..! So I keep turning it and it's turning fine and then again, the camshaft kind of slips and goes fast clockwise maybe 90 degrees while the crankshaft is stationary. I was able to feed a new chain in and rivet it. The timing now is 20 degrees advanced. I had all of my injectors out when I was changing the chain. Maybe the vacuum pump caused the camshaft to slip like that since the vacuum pump is spring loaded? Please help."