1966 250se Bosch Injection Pump Questions - Mercedes-Benz Forum
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post #1 of 19 (permalink) Old 04-10-2019, 01:00 PM Thread Starter
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1966 250se Bosch Injection Pump Questions

Hi everyone,

I have a few questions about the injection pump on my 66 250se coupe. The pump is full with clean oil, but when turning this pump by hand on the bench, it seems very clunky and noisy compared to my 300TD pump. The diesel pump is smooth with very distinct piston/plunger engagement. When turning the diesel, it's repetitive when each piston is engaged/released, thud thud thud thud thud. The 250se pump doesn't feel as smooth and there's no distinct sound/feel when a plunger is engaging. The 250se is more like grind, clunk, clunk, grind, noise, clunk. It doesn't seem right. Is this normal? The original owner had the pump tested for equal fuel delivery, etc and it checked out good by a Bosch tech. I don't remember the tech who did the testing, but the receipt showed they ran it and tested equal flow, and it tested good. Seems almost like a bad bearing? Maybe that's just the way these are?

I'm not familiar with these and want to make sure all is ok before I install it. Does anyone have one they could spin and give me ideas?

Thanks, Jim
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post #2 of 19 (permalink) Old 04-17-2019, 12:37 PM
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Do you have an injection pump shop around anywhere near you?
The governor weights might make a little noise when turning the pump over, but the cam and roller followers should be quiet.
The gas engine pumps will feel a little looser because they don't have to generate as much pressure as the diesel ones..
Dave
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post #3 of 19 (permalink) Old 04-18-2019, 05:52 AM Thread Starter
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Hi Dave,

There is a Bosch injection shop about an hour away. I connected the pump to my lathe and spun it at different speeds, and it sounded fine. Turning it by hand slowly seemed clunky. You're correct on the governor noise. I plan on installing it this weekend and getting the car back on the road. Thanks for the good info.

Jim
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post #4 of 19 (permalink) Old 04-18-2019, 07:33 AM
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You probably already know this, but the position that you install the pump in (meaning the rotation of the pump at the time you install it) needs to correspond to a specific position of the engine at the same time. I don't know what those are, I'm just saying it shouldn't be installed in a random position.

Currently: 1965 300SE Lang, 1972 Alfa GTV, 1959 Borgward Isabelle Coupé
Past: 1965 250 SL, 1963 220 Sb, 1971 250 C, 1985 300 TD, 1967 250 S, 1968 280 S,1981 300 D, 1982 280CE, 3 Facel Vegas, Borgward Isabella Coupe, Alfa 2600 Sprint, Volvo P1900 (yes), numerous less interesting Volvos, ...
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post #5 of 19 (permalink) Old 04-18-2019, 04:36 PM Thread Starter
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Hi Scoot, I installed it with the two marks aligned on the pump, and the engine at 20 degrees ATDC. That's the reference the Mercedes manual has for it. Hope this is ok?

Jim
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post #6 of 19 (permalink) Old 04-18-2019, 05:04 PM
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Hi Scoot, I installed it with the two marks aligned on the pump, and the engine at 20 degrees ATDC. That's the reference the Mercedes manual has for it. Hope this is ok?
Probably that's what it should be. I don't remember other than remembering that it matters. Hope it runs great! When will we know?

Currently: 1965 300SE Lang, 1972 Alfa GTV, 1959 Borgward Isabelle Coupé
Past: 1965 250 SL, 1963 220 Sb, 1971 250 C, 1985 300 TD, 1967 250 S, 1968 280 S,1981 300 D, 1982 280CE, 3 Facel Vegas, Borgward Isabella Coupe, Alfa 2600 Sprint, Volvo P1900 (yes), numerous less interesting Volvos, ...
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post #7 of 19 (permalink) Old 04-19-2019, 08:32 AM Thread Starter
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I hope to know soon. I need to clean the fuel lines, injector lines, injectors, filters, and gas tank.
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post #8 of 19 (permalink) Old 04-19-2019, 11:54 AM
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Is this a two plunger pump or the later six plunger?

Dan
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post #9 of 19 (permalink) Old 04-19-2019, 01:02 PM Thread Starter
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Dan, it's a six plunger, 250sec.

Jim
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post #10 of 19 (permalink) Old 04-19-2019, 01:07 PM
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Dan, it's a six plunger, 250sec.

Jim
Thanks, Jim, I figured that was the case. Just curious, as I've got a two plunger on my 65 220SEb with the M127, and it's a rather unique system. I just found a factory service manual for the injection system and it's made for some fascinating reading.

For example, the volume of the pipes that connect the pump to the delivery valve blocks is a critical measurement, and should be checked whenever the pipes are replaced.

I love to know how things work, and the two plunger system is a really amazing feat of engineering.

Dan
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