6.9

The scenario of a bent rod is a possibility but let's hope it is less severe. In talking with the shop, the starter is also suspect. Things to look for....when you took out the spark plugs, did you notice any fuel that spilled out? Were any plugs wet with raw fuel? With the engine not turning either way ( it could still turn slightly with a bent rod unless it's totally jammed ), it could be the starter and the ring gear. Try removing the starter and rotate with the breaker bar. 

Dave, do  you want the bad news or the really bad news?

Unfortunately it sounds like you probably bent a connecting rod.  The 6.9 that I have was purchased from a junk yard and was in there for the same reason, #8 piston was broken and jammed into the cylinder by the bent rod.  If the fuel distributor piston sticks in the "up" position, as soon as the fuel pump turns on those injectors will be dumping fuel into the cylinders.  The cylinder that happens to be full of liquid fuel and is on the compression stroke is the one that will end up bending the rod because, as we know, you can't compress a liquid.  The starter motor can generate enough torque to do it, but most likely when it tried to fire on the other cylinders, it created enough torque to do it.  You will have to pull the engine apart to see how bad the carnage is.  Hopefully there is no damage to the cylinder wall or the engine block. You will at the very least, need a piston and connecting rod.  

Sorry to hear this happened to you.  It's a good reminder of what can happen when a fuel distributor is not working properly, it's a rare event, but it can happen.

I have some parts in my stockpile, if you happen to need anything.  Might be more cost effective to find another engine though.

Good luck,
Chris

[cross posted on W116 board]

[u]Background:[/u] After doing Fuel Distributor work I tried to start the engine. I messed up the FD a little and flooded the engine. I then rectified the FD and tried to start again. The engine was firing and almost started. It stopped abruptly however, with a hard clunk. In the process I apparently cranked too hard for too long and burned out the starter. I replaced the starter with a rebuilt unit from a reputable source. On the next try the engine cranked about 1/2 a revolution and stopped abruptly with the same hard clunk. Thereafter it wouldn't crank at all.

[u]What I tried and looked at[/u]:
[list]
[li]Removed starter, cover plate on the opposite side and the plate at the bottom of the bell housing to see what I could see of the ring gear. Everything visible looked OK. Obviously I could only see a fraction of the ring gear.[/li]
[li]I tried rotate the engine with a giant breaker bar on the 50mm bolt on the harmonic balancer. It was impossible for me to turn it [i]at all[/i]. Absolutely no movement of the crankshaft. [/li]
[li]I removed spark plugs. Even with plugs in it should turn, but why not try anyway? No change. It was clear that the plugs were black and sooty from running way too rich while trying to start. I'm sure that will burn off if I ever get running again.[/li]
[li]I removed one valve cover to have a look. No obvious issues there (broken springs, destroyed chain or whatever). I'll look at the other one tomorrow, but I'm not holding my breath.[/li]
[/list]

In all cases I tried rotating CW (the right way) but also CCW just to see if it would go backwards even a tiny amount. It didn't - jammed solid in both directions. I'm using a 24" breaker bar and lots of muscle to turn it over. There is absolutely zero crankshaft movement. Clearly something is jamming the crankshaft. I think it's significant that after the first clunk the new starter DID rotate it a little but was followed by the same clunk.

Now I've now exhausted all my logic and am at my wits end. Clearly something is jamming the crankshaft. I'll try any ideas, however far fetched. Thanks for any and all help. Cheers,




Dave

1977 450SEL 6.9, No.923