I've replaced the engine in an '81 240d with one purchased on craigslist from a guy who allegedly bought it from a wrecking yard for a project he subsequently abandoned. The old engine died from oil starvation after spinning a rod bearing. I've no reason to suspect that the new engine is bad, but natrually I'm aware of the risk that it is.
All is reconnected, fluids topped, etc. I prime the pump with the plunger thingie, and start cranking.
After many minutes of cranking, and a couple of new charges on the battery, the engine began to sputter. I figured that one more charge on the battery would do it. But after that fresh charge, when I turned the key, I got only a clunk. The solenoid does its thing, the starter tries, but the engine doesn't turn.
I concluded at first that I'd overtaxed the starter, so I took it out, gave it a good cleaning and greasing, and put it back in. Still only a clunk. I swapped the starter and cables with a known good set from another car. Still only a clunk. The cables get warm, so current if flowing. Ok, it's not the starter.
I took out the injectors and glow plugs. As you would expect, it cranked freely now. I replaced them all with known good units. Once again, it cranked freely, but with no signs of life. And after a while, back to the clunk. I'm back to the same point again.
Somehow, the engine seems to get into a state where it won't turn over with the torque the starter has available. Am I filling one combustion chamber with fuel and causing a hydraulic lock or something?
I'm new to diesels. What am I missing here?
Thanks in advance for any wisdom you might offer. I'm running out of ideas.
-Paul

First - No secret to firing these up. You are not missing anything.

Let's reduce the possible problems, and get the starter behaving as it should.

Compression. After no fuel, having enough compression would keep you from firing.
If you do not have a compression tester, borrow one. If the compression
is too low (under... 250 ?? maybe the others can chime in with how low can you go) then it will not fire no matter what you do.

After confirming the compression is okay, then confirm the fuel is at the injectors.
Just crack the nut holding the line at the injector and make sure fuel leaks out
when cranked. We will assume that the injector pump is in its original position
and it is not a timing issue.

Now, about that starter. Don't crank for more than... maybe 30 seconds,
maybe a minute - but then you have to let it cool down - almost ten minutes.

When you say CLUNK, try and determine by the sound what is clunking.
Is the solenoid engaging the flywheel ? Then stopping dead.
You say it spins with glow plug removed, makes me think the engine
is freely spinning and not locked up, which leaves the starter unable to
produce the torque needed.

Are the cables connecting the starter original MB with wires molded into
soldered into the leads on the ends ?
If not, and they are auto store replacements with bolt/clamp for the wire
you may not be getting enough current to the starter. Enough to engage but not enough to turn. The tip off is those hot cables.

Generally speaking, fuel and air are all that is needed.
In the moderate temperatures we are having now you should even be
able to start without working glow plugs.
But if you think those are acting up test each one by directly connecting
to a battery or charger, forget the resistance test. It is easier to just
watch them turn bright red. The glow plugs can be hooked directly to the battery or charger to get it started, but I'll bet that is not it.

__________________
80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250

Thanks for the tips!
I don't have a compression tester. This is probably where I should start. I've seen several posts regarding the kit from Harbor Freight, I think, so I'll get one coming.
In a gas engine, one can drop some oil down the spark plug hole and test it that way as well. What's the best method for the diesel? Same thing, but down the glow plug hole? Or not at all?
I beileve the clunk is the starter pinion engaging the flywheel, and giving it its all, but it isn't enough. The fan blade can be seen to budge, but only an inch or two, and then when the key is released, returns to where it was. There isn't enough torque available to turn it over, but it isn't absolutely clear whether there isn't enough available, or whether what's required by the engine is more than it should be.
When I had the lines off to pull the injectors, three of them had fuel in them, but one did not.
I haven't tried cranking with the lines loose, so I'll give that a try.

if the motor is hydrolocked, you should be able to tell by pulling the GP's and seeing what sprays out.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

How low can you go? Check post #52.

a challenge for veterans....where to start?

Hope it's not the same problem.

__________________
79 300SD - $50 out of pocket purchase
03 Dodge Ram 3500 CTD
2003 VW Jetta TDI

Well, I found the problem.
I took off the valve cover, and found that the cam didn't turn when I bumped the crank around with the fan blade. The tensioner had LOTS of slack. I pulled on the slack side of the chain, and this is what I found:

close up:

So what did I do? I took an engine out of a crate (with an unknown history, taken pretty much on the say-so of the private seller), bolted it into a car, and cranked it (a lot) in hopes that it would start. I recall a few odd sounds, but nothing really dramatic. After a while, it wouldn't turn any more, as the earlier posts describe.
Now I have one engine with a bad crank, and another with a broken cam chain, and I suppose possibly bent valves.
Did I violate some cardinal rule of Benz-dom?
What about that reputation for being bullet proof? How could I have killed an engine by cranking it over too much?
Or was this engine bad to begin with?
WTF???

Time to send these photos to the seller and see what he says.

__________________
DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

Looks like the seller owes you a refund or a good engine.

I don't think that happened by cranking.

__________________
80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250