80 300sd Timing Issues - Died No Restart
 

Here is a strange one for you; I was driving my car when suddenly it died w/o warning. (Although it has been making a rattling sound - classic indication of a timing chain failure) I attempted to restart and the starter motor wouldn't turn the engine over until I let it sit for a minute or so. I towed the car home and hooked a 500-amp starter to it and cranked and cranked until it started, while running I could hear a clicking sound from the front of the engine. Then it died again after a loud click and returned to the previous state. It almost seems the timing chain is somehow slipping! I have a new chain and associated rails, guides, ect. I have 5 days to wait for the chain press tool to come in so any suggestions would be helpful!!! I am thinking a link or two came loose from the chain and is allowing it to hop gears, or one of the keys (better not be crankshaft) broke. Any ideas?? - Thanks ~ William

Sounds like the tensioner failed and allowed the chain to jump on the crankshaft.

Take the valve cover off and inspect the visible part of the chain. It's not broken or you wouldn't be able to get it started.

The problem may be obvious, may not. At any rate, check condition of rails, get a new tensioner, and turn engine to align the mark on the cam with the mark on the front cam tower. This is not very precise, but if you then look at the crank pulley you should be able to tell how far out the timing is -- more than 8 degrees is trouble. I suspect you will find more than that if the chain jumped.

If you are more than a tooth off, the cam towers will be broken from valve to piston interference.

Pull a new chain through, then re-set injection timing and cam timing.

Peter

I pulled the cover and did not see any broken towers. The timing however is way off. Is it possible that it didnt damage the valvetrain at all? How hard are the heads to take off on these cars? ive done plenty of gasoline cars but never thought id have to pull the head on this one! I still havent looked too far into the cause of the slippage, any more ideas? I am going to tow it to my shop tonight and see what I can find.

OK, I pulled the radiator, fan, oil cooler, (I decided to change the radiator while I’m in here, BIG HOLE) valve cover, and the air cleaner. I see nothing gone too wrong except I cant turn the engine over with a socket on the crank! Even with a cheater bar! The starter will turn the engine over though, which seems really strange. What the heck could cause this? Are these engines this stiff? If I take the lower oil pan off can I see the bottom of the chain/ crank gear at all? Any Ideas what could cause this strange behavior? Tonight I plan to do some more disassembly so any tips would be great!!

Well it does have 22:1 compression ratio, try removing the glowplugs if your having that much trouble.

I did some more disassembly and it turns out that the valves were preventing the pistons from moving. Back to my question, how hard is it to do a valve job on these cars?

Valve job isn't too bad. Just insist that that ture OEM guides are used, and they are left alone unless the valve can't be insterted -- no reaming for "clearance" -- make sure the exhaust guides are the original bronze ones.

Removal isn't too bad -- there are a couple or three screws in the chain case that must be removed in order to get the head off, they aren't very obvious.

When you put it back together, you can set the inital valve clearance on the bench, then pull the follower towers back off (you have to -- the head bolts are underneath!) -- valves will still be adjusted when you re-install the towers.

You will have to check the injection timing -- no was to tell if the chain jumped on the cam sprocket or crank sprocket (mostly likely the cam, but?)

Peter