Need Advice. Engine failure
 

I own a 1979 Mercedes 240d with the om616 engine. I used to frequent the forum a while ago but wasn't too active with posts and replying. But now I need some help and advice. Here is the back story; driving the car at around 35mph, loud bang and engine shuts off. I pull to the side of the road and try to crank the engine three times but it doesn't start. I have the car towed home and do a visual inspection. There was a spot of oil on the inner fender well that looks like it came from under the valve cover with fairly high pressure but other than that everything looked intact. Upon removing the valve cover I find that the timing chain has broken in between the links and I can just pull it out. From there the car sat for 2 months until today when I removed the head. It looks like the valves contacted the piston on cylinder 2 and 4. No valves were bent and came out of the head just fine. The camshaft is toast as well as the rocker arms. With the head removed the crank spins freely and does not bind. Here is where I need the help. I need to know if the pistons can be reused or if I need to go through the whole block. I have attached pictures of where the valves contacted the block. Also, when looking at the cylinder walls the factory cross thatch pattern is still visible, only problem is on cylinder 2 there is a visible scratch on the cylinder wall. So what do you guys think, are the pistons okay to reuse as well as the block? What test can I do to provide peace of mind? If needed I can provide more pictures.

I am not a heavy engine guy but this is what I know. BTDT the hard way.

1) It is very unusual not to have bent valves as it is an interference engine. You were driving slow so you may have dodged a bullet.
2) The scratch on the cylinder wall could indicate a broken compression or oil ring. I had the same scratch on an OM603 engine. You cannot tell unless you push the piston out.
3) Need to find out why the chain snapped. Chain fatigue or something in the way and snapped it.

Other may chime in. Hope this help.

I was surprised as well that no valves were damaged. I removed every single valve and none were bent and the brass bushing were intact.
As with the scratch I don't know if it scored or just a surface imperfection. With a finger nail you cannot feel it. I did not examine it closely and it is dark out.
The chain snapped on what I believe to be my fault. I bought the engine not running and figured out the the timing skipped a tooth. I did not replace the chain at the time or measure for stretch. I think it was stretched from the previous repair and it was just its time to go. I ran about 40,000 miles from the last time I fixed the timing.

Have been down this road on two 240D's, a 76 and a 78. Neither one bent valves and the pistons were fine on both. Both broke the camshaft towers.

The piston in the last picture shows a lot of pitting, more than I would say is ok. The scratch on the cylinder is also concerning.

How did it run before the chain broke?

Can you post better pictures of each piston?

Did your towers snap?

I don't know why the chain broke on the 76 as I bought it that way. The chain broke on the 78 because the front main bearing failed: thereby, stopping oil flow to the chain and it snapped. The bearing failed because I had the bearing fitted too tightly.

The pistons are not actually pitted, there is just carbon deposits on them. As for the scratch, when you run your finger across it you cannot feel it. Only when you run your fingernail across it can you feel a very slight imperfection.

The engine ran fine until the chain broke, it happened all of a sudden. Only thing to note is that under load and high rpm there was a noise coming from the front of the vehicle. I could not replicate it under normal conditions and whether it has any correlation to the chain breaking I don't know. I tried to dianose the noise but I could not narrow it down. It could have been anything, my a/c pump is seized, my alternator pulley makes noise, or just normal diesel noise, I don't know.

My tower are intact. The arms and camshaft lobes have very bad wear and scoring on them. The only thing that actually broke was the chain.

I will try to take pictures tomorrow, it is dark outside.

Personal decision
 

This is a personal decision.

If this where my vehicle........................................

#1. Replace the valve guides, regardless.
#2. Replace the cam shaft and towers.
#3. Install a new head gasket.
#4. Install a new timing chain.

Enjoy the car.

IMO: Going further may well run $3k - $7k, depending on parts / labor.
Unless you are prepared to do 100% of the work, and live without the vehicle a month or more.

.

Good advice from all, so I will add nothing, except to ask, how many miles on the car when it happened and was it the original chain??

The car had 232,385 miles on the original timing chain.

There are about three headgasket designs... MB kept tweaking them... check the holes on the head and then use the latest design which will fit...
Be sure to replace anything which touches the chain .... rails, etc...
Might be better to find a running replacement engine and slap that in ... sometimes available for a few hundred dollars.... and if you want... keep that one to work on at your leisure....
If you can find a paper 616 manual you will be in much better position to do this right....

That was the plan, to go through the top end. New valves, valve guides, timing chain, timing chain tensioner, timing chain guides, full engine reseal kit, and do work on the cooling system while I am in there. All the work will be done by me on days off and evenings. The vehicle has already bee sitting for around three months and I expect it to sit another three at the pace I am going.

I thought about just fixing the head and then putting the engine back together but I just wanted to get some opinions from the mercedes gurus on the forum.

To do this right.....
you need to take out the pistons.... inspect and measure them according to the manual..
put in new sleeves..... and then bore each sleeve to fit EACH piston which is going into it...
These things are detailed in the paper 616 manual ...

the reason the majority of motors with valve contact result in bent valves is the valve angle is often canted and the valve face contacts the piston at an angle, resulting in a bend.

the 61x design engine (and others I'm sure...) has a nearly perfect flat valve angle to the piston face. so, when valve and pistons collide, they slam full force into the cam... instead of bending the valves. on the turbo motors, the valves nearly always need to be replaced after contact, as the exhaust valves are hollow, filled with sodium. but the NA motors have THICK solid valve stems, and rarely get damaged from contact.
the piston on the other hand, often gets banged pretty bad, and the dent sometimes makes that piston unusable, depending on how many times the contact is made...

The valve slap would concern me. Before going further, I would definitely check piston protrusion height in all the cylinders to determine if there is a bent rod.

The other thing that concerns me is the cylinder bore scratch even though you stated you can't feel it. It could be caused by carbon debris, in which you can probably leave it. But if it is ring related, you'll have issues later on. I would seriously consider removing the piston and inspect it. But if you do one, I'd do them all.

I do agree with this but at the same time I think that that is also a lot of money to spend on an OM616

Rough estimates for what I'd expect that to cost here in clog land =>

head gasket 80 euros - timing chain 80 euros (IWIS) - camshaft is about 100 euros (last time I looked) - should replace followers (about 25 euros each => 200 euros) - camshaft towers good second hand about 30 euros each => 150 euros (I think there are 5!) - valve guides are cheap but then valve seats need to be re-cut and then the valve should ideally be re-ground so a redone head is at least 300 euros here...

...that's the best part of a grand

Now I know clog land != US of A but you know even with a fair amount of smart shopping I can't imagine it is going to be much under $500

I'm not trying to be negative but - well - you know????

Agreed