Any decent Bosch shop will be able to look up your pump and see the parts list, and also check on availability of a new part from Bosch. Who knows, they might have some hidden away somewhere. The spring probably isn't a part that's changed often.

__________________
- Greg -
1973 220D, The Prodigal Benz
1974 240D

So.. pressured tested via the glow plugs (which are in great condition too).

Over just over 300psi on a stone cold engine with wot. Book says 319-348psi on hot engine. I assume rings etc would all expand and give a higher reading hot?

Reassembled the governor, all working well and holding vac. New oil seals on spindle and all cleaned out and greased in poppet cam. No leaks.

So even with glow plugs it a bit of a while until it will fire into life and stalls out etc until it’s warmed enough to run smooth.

Once warm some light blue smoke on idle suggesting valve stem seals (I have a set for it) which clears when you increase rpm to nothing at all smoke wise.

But blip the throttle up and you get a nice puff of black (too much black). This is the black that will show up under load.

Question is, timing advance device? Can they go faulty? Could that cause timing to be staying static?

Initia ip timing, in my mind advancing will burn ‘better’ but others also say more advanced you are the more black and retarding removes black smoke. It’s a 615.941 engine. Am I right at 24 degrees?


Thanks

I've experienced similar symptoms on my OM616.916 240d and am based in the UK as well.

Here's what I recommend in order to eliminate the problem entirely (apologies if any have already been done):

1) Two bottles of Diesel Purge, then
2) Replace all 3 filters (including tank screen)
3) Rebuild injectors with Monark or Bosio Nozzles only (see link below)
4) Rebuild lifter pump & replace attached hand primer pump (see link below)
5) Replace OFV spring (see link below)
6) Replace diesel injection pump delivery washers/ o-rings
7) Optional but highly recommended: simultaneously with 1), use two bottles of Auto-RX following the instructions to the letter. While ARX will not address the smoking issue, it will raise compression in anything but a worn metal motor.

https://dieselfuelinjector.guru

Mark will provide 3-5 for you. I followed the above list in both my W115 and W123 diesels and the motors now run like new. While it may appear daunting, a few hundred $ has led to a dramatic transformation in both vehicles. No smoke on throttle or idle, 30+ mpg and smoother, quieter operation.

__________________
Why I will never do business with "DieselKraut" again

http://www.peachparts.com/shopforum/mercedes-benz-used-parts-sale-wanted/378935-why-i-will-never-do-business-dieselkraut-again.html

Managed to get a a proper compression test done today, with a warm engine and removed injectors.

All cylinders showing around 400psi, within 10% of one and other.

I don’t think I have a compression issue.

Two variables left then…

Injection timing and the volume of fuel entering…

Maybe there's nothing seriously wrong with it. It is a 60HP engine pushing a 6000 pound vehicle.

__________________
- Greg -
1973 220D, The Prodigal Benz
1974 240D

If this were my situation, and I doubted the calibration of the pump because of what looked like a stretched compression spring in the governor, I'd find a Bosch shop that knows these older pumps and have the thing checked out by them.

Sourcing a new spring is only part of the equation. Calibrating the pump's output is best done on a test stand, by the book. I suppose one could install a new spring and go through a lot of trial and error until it "seems right", but that could require hours and hours of effort, and the results could still be less than ideal.

I doubt the timing device is faulty. I don't think I've ever read about someone having problems with one. 24 degrees timing advance is right for engines installed in cars. It's probably the same for the Unimog.

__________________
- Greg -
1973 220D, The Prodigal Benz
1974 240D

Thanks again for the thoughts.

Have spent some more time on the engine today.

Timing is spot on 24 degrees, I retarded it right back just to check the correct outcome and surely it pumped out plenty of grey diesel mist and ran rough.

Re timed back to 24 and runs smooth again, perhaps needs a little more advance but have run out of movement on the pump slots.

Fuel line from lift pump when primed with primer shows some air bubbles, I guess this could be from the fuel line/tank pick up. Will inspect this. Doesn’t seem to have any when running though.

Injectors, I pop tested them all again and went with the German Bosch nozzles, spray pattern is nice but it seems opening is too early, opening between 1000psi and 1200 psi across the 4 of them. Have ordered a set of shims and will correct, should be about 1650. May be causing more fuel injection than required and earlier.

Lack of power is miserable though, it bogs down and blacks.

You could get away with a couple more degrees advance timing. I've set the timing in the '74 at 26 degrees before TDC and it runs great. Too bad you have to pull the IP to re-index it to make that happen. If you have a shop check the pump you'll have it out anyway, though.

Keep after it!

__________________
- Greg -
1973 220D, The Prodigal Benz
1974 240D

Having researched a few more bits..

The engine is an om615.941.

The injection pump is a PES-4-M55C-320-RS47, this shows in the charts as one for the OM616.916 engine. Still pneumatic governor..

How much difference is this likely to be giving? From what I can see they should at least be timed a couple of degrees in advance.

Hmmm, I wonder if that pump was installed as a replacement for the original. The fact that you cannot rotate the pump for more advance could indicate that is was installed a tooth or two off, which is not something I would expect from a factory installation.

According to the charts, the OM615.941 should have PES 4 M 55 C 320 RS 60. The list shows that the governors for OM615.941 and OM616.916 are different, and this difference might come down to which springs were installed in them. It's also possible that these pumps do not share the same diameter plunger elements.

This mystery, along with the apparently stretched spring in your pump's governor, leads me to believe even more strongly that you could use the help of a good Bosch diesel shop to get things sorted out.

__________________
- Greg -
1973 220D, The Prodigal Benz
1974 240D

Spoken with my local bosh guys today, they were able to pull up lots of info and suggested a few bits.. they can also setup on bench if required.

The 616 it’s from was in the 240d and only difference being 200cc and 5bhp, they felt fuelling difference would be minimal. In shops opinion full load stop adjustment should suffice in terms of limiting fuel output and to check effectiveness of the adjustment ie actually acting on rack travel. They also thought timing should be more advanced if I’m still getting some grey/white on idle.

Sounds like I need to pull pump as you say and check alignment of notch.

They said if all else fails then drop it in for a test and adjustment.

I had thought all 616 diesels were block fed oiled, seems this type wasn’t.

Hi all,

Just double checking something before I lose the plot entirely.

IP timing mark on the pump won’t line up naturally, it’s like it’s 2/3 of the way there and springs way past it or sits about 3 teeth retarded in front of it.

To account for that I had to set the crank at around 35 btdc then insert the pump. Wind the engine to around 24-25 btdc and then drip time it to one per second.

Once finally clear the air it starts and runs, sounds ok but steady stream of blue/grey smoke on idle.

As above the engine has very good compression, just over 400psi on all cylinders.

Any further thoughts?

Thanks

There's a fair amount of flexibility in injection timing. If you are anywhere near the ballpark it should run OK. I've pushed timing way far advanced, like 1/4 inch of IP movement towards the engine, and it still ran and drove OK. It was a PITA to start but it ran. I did that when I was trying to figure out why the engine wasn't running well, before I discovered the leaky governor. wendy's lunch time surveyzop.com