I guess I don't really understand how pop pressure would significantly alter timing, but I'll admit I don't fully understand the working of the injection pump. Isn't diesel non-compressible? When the elements fill as far as the rack determines with fuel, is the balance filled with air? The air would compress, but at the pressures we are talking, I would think the difference in element compression would be negligible.

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'82 300SD - Somewhere over 220k - Becoming reliable...

your engine turns over 41.66 times in one second, which would be .024 seconds for one revolution. I forget, but let's say the fuel is injected 24 degrees before top dead center. 24 degrees is 1/15 of a revolution, which should mean that it takes 1.6 one-thousanths of a second more to reach top of dead center.

It tells me one should not mess with the injection pump, but not whether the injector at higher open pressure affects timing enough to change things. Doesn't the timing tend to occur earlier on an unadjusted car, like a degree or two out of spec?

Most fluids don't really compress, and air in your pump or lines means your car probably won't start.

No, the normal tendency is for the injection timing to become retarded. I will bet that the majority of the 616/617 engines on the road today are 8-10 degrees retarded.

Thanks Tangofox007, 10 seems like a big number, though. My timing chain seems pretty tight, so I don't think I am that far out of whack. When you advance it back into spec, what does that do for mileage?

I don't have any data on mileage. The biggest noticable (through casual observation) difference is that the engine will start much faster.

Reckon the tensioner has something to do with that?

a chain nearly ready to snap from wear will still feel "pretty tight" because there is a tensioner in the route, that keeps it from slapping around.

the ONLY way to test wear or "stretch" in a chain is to measure the alignment of the crank in relation to the cam.

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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 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

this is how I mentally reason about it:

the injection pump's cam is spinning, and a lobe on its cam starts to push one of the elements up. in theory, the diesel fuel, the steel lines, and all other hardware are incompressible, and in that theoretical dream land, the pressure would instantaneously jump to 135 bar the moment the element started moving, and the injector nozzle would open.

in practice, the system as a whole compresses just a little. this means it take a tiny bit of extra time for the pressure to build to 135 bar. that extra time translates to extra crank rotation, which means timing retardation.

so it'll take more time for the system to get to, say, 170 bar, which means the point at which the injector nozzle opens will occur later, at a retarded point of timing.

the reason I've thought about this is that I was considering increasing my pop pressure, for two reasons:

* decrease the potential of injector coking if you idle for days on end (it'd be cool to use my engine as a generator should I buy a weekend-getaway workshop out in the woods).

* very, very slightly increase the fuel mileage (increased injection pressure more finely atomizes the fuel. this is one of the reasons common rail operating at 1000+ bar results in more efficient combustion).

the reason I had targeted 170 bar was that I had heard that Mercedes put some OM617's in industrial equipment which was expected to idle for long periods of time, and they spec'ed a pop pressure of 170 bar. this would seem to indicate that's a safe pressure for the pump to operate at.

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OM617 in a 67 chevy pickup http://tinyurl.com/projectgmbenz

Looks like a great job. I have to pass something on to you. This guy was painting some trim on my neighbor's house, only two days ago. It turns out that he is a car nut and from Argentina. He owns a number of these old Mercedes, including something from the 1930s that is the only one of its kind in the US, and it is car number 11. He tells me that you can take your old fifties Chevy truck into a shop down there and drive out the next day with a rebuilt seventies or eighties cast iron Mercedes diesel. He, also, said it was the best place in the world to have your IP worked on. Too bad it is too far away. Cell, out of curiosity, where did you get the idea to plug this into a Chevy truck?

There are two Bosch service centers listed near me for pump repair. One said they said to use the other location for my car, and the other location did not give me that warm, fuzzy feeling when I visited.

Wow, sounds like my kind of shop! Here's the genesis of the idea. I had audited a thermodynamics course while working at the university of Texas at Austin, at which point I fell in love with the diesel combustion process.

After doing a lot of reading, I then found out about the longevity of diesel motors. Two examples stood out in particular: the legend of the half million mile motors: the cummins 6bt and the mercedes om617.

I was lusting after the 4bt the 4 cylinder version of the 6bt), but an advertisement on craigslist for a 78 300SD caught my eye, and I drove it home that day with a big assed grin on my face.

Should my truck ever get totaled (and I somehow survive), I'd like to do this next: 4BT in a 1947 Ford 1.t Ton Dually... I got the cab mounted!! (convert a 4bt-powered step van into a pickup)

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OM617 in a 67 chevy pickup http://tinyurl.com/projectgmbenz

OK, thats what I thought. Also explains why those piezo timing lights don't translate directly to the static timing spec, although if one were to get a baseline with injectors at 135 you could use one of those to bring injectors set at 170 up to correct timing.

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'82 300SD - Somewhere over 220k - Becoming reliable...

How does a Linux guy learn to weld like that?

Are you one of them rednecks that know all about this stuff?

I was down in TX about 11 years ago, and I was traveling west on this two lane highway (it was an absolutely straight line) to Austin doing plus 90 MPH. I was about an hour east of Austin, and saw all of these old cars sitting outside. I slammed on the brakes, as I had to check out this place.

Inside was even more interesting. A 100-120,000 square foot a/c building with a 1940s fully restored fire engine, a bunch of 1930s Ford converts, model Ts, hundreds of antiques, it was a stitch. You know this place?