I am having a very hard time understanding the factory service manual on installing the recently serviced fuel injection pump in my 1968 W110 200D OM621. I don't know what I am supposed to do at this point. I have the engine set to 47 degrees BTDC, or at least as close as I could get it since it moves so jerkily.

The factory service manual states that the first cylinder must be in its compression stroke position. As opposed to what, exhaust stroke position? How am I supposed to know if the first cylinder is in compression stroke position?

Then it states that the injection pump must be placed in start delivery position, meaning the mark on the splined collar lines up with the mark on the pump. It looks like that's the way I got it back, so that part is fine.

Then it says so apply "light leftward oriented pressure to the drive collar, opposite to the direction of rotation". Then it reads, "Cam pressure of the camshaft causes the drive collar to jump back two teeth to the cam base circle. The second tooth must then coincide with the marking on the injection pump housing."

What is that supposed to mean? I'm assuming the pump turns clockwise when facing the engine. Is the mark on the pump supposed to line up with the second tooth on the drive collar (and what side?) instead of the missing tooth? I rotated the drive collar and found that I couldn't get the missing tooth and the mark on the pump to line up anymore.

Then there is a note: "Because the drive collar jumps back by two teeth, crankshaft adjustment to 47 degress BTDC is necessary." Once again, I have no idea what this means.

This whole "apply light leftward oriented pressure to the drive collar", the drive collar "jumping back two teeth", and the first cylinder "in its compression stroke" is confusing me and now I don't know what to do.

The pump is resting in the engine with the "missing" tooth on the drive collar almost aligned with the mark on the pump. I couldn't get the marks to line up perfectly after rotating the drive collar. The engine is set at 47 degress BTDC and I have no idea if the first piston is in its compression stroke. And what if I'm off a tooth or two?

Where do I go from here?

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1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 350,000+ Miles