OM606 Cam Timing Jumped 20 Degrees
 

On my way home form vacation last week I was driving down I95 and my daughter mentioned the engine in the '95 E300 sounded loud.

Shortly afterwards I pulled off on exit and it sounded really loud and diesel-ly, link a cold semi truck.

The idle was very rough, black and Smokey and it was a pain to start.
We drove the next 300 miles home and after looking for all the usual things like clogged filters, air leaks, stuck egr valve, or a blocked exhaust.
I was at the end of my rope as to why it started doing this all of a sudden.

Just for kicks I pulled the valve cover (and noticed the previous owner had left me a few broken glow plugs, ouch) and checked the cam timing.
To my amazement it was at 20 degrees before top dead center.
I triple checked it to make sure and looked for reasons why this could have happened.
The chain is not slack and there are no loose or broken components that I can find. If there was I'm sure there would have been a catastrophic failure during the drive home.

So it is easy enough to unbolt the timing gear from the cam and re-set the timing but without understanding what happened I don't know if it will happen again.

Does anyone have a clue?
Maybe this has happened to someone else?

How long have you owned it? Maybe somebody installed a new chain with a link off.

I've put a little over 30 thousand miles on the car sine I've owned it and this just started maybe 350 miles ago.

It jumped time by 20 degrees and you haven't damaged anything... jeeze!

I don't know the details but I believe your Camshaft Gear is not attached in the conventional manner as the 617 Engines are.

http://www.peachparts.com/diy/om606t...stretch/01.jpg

Looks a little different....

Remove tensioner, unbolt the cam sprocket, rotate engine forward to TDC, move cam sprocket however many teeth it takes to line up, replace cam sprocket, replace tensioner, check IP timing. If I counted correctly the sprocket has 36 teeth which means a one tooth jump is 10 cam degrees and 20 crank degrees. I'm guessing that maybe the tensioner is weak or one of the check balls got stuck and it depressuized temporarily which allowed the timing chain to jump.

It would be wise to pull the chain cover and completely overhaul the system. You just dodged a a really large bullet.

Really?

The pointer plate on the OM606 is not like the old engines, its a moveable part, if someone took off the waterpump and removed it without marking its placement relative to the crank pulley it will never show correct engine timing.

I doubt the engine will actually run with 20 degrees off timing, the pistons will collide with the valves.

The water pump was replaced by the previous owner. I don't know how adjustable the timing pointer is and would only expect it to go a few degrees in either direction. After work today I'm going to check the IP timing and see if it shows the same offset the cam timing does.

The same exact thing happened to my 74 240D.
The problem. The key in the governor shaft had plowed the key-way almost half way around the shaft. I remover the shaft and had a machine shop cut a new key-way 180deg from the original. Never could find out what had placed such a tremendous force on the shaft. The difference in timing came on slowly over a few weeks,not all at once. After pulling the rad the job was fairly easy.

I measured the injection pump timing and it is off by the same 20 degrees. Since the timing chain and guide rails show no signs of malfunction and it didn't self destruct while I was driving I am going to guess that the goober that replaced the water pump did not install the pointer correctly. So I'm going to button it all back up and run lift pump pressure and compression tests to see what I can see.

I have made the mistake of looking at cam timing based on the wrong part of the pointer near the balancer. Are you using the blade part as your point of reference?

Yes I am, the part that you cn hardly see because the belt tensioner is in the way.