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Bosch M pump timing question
mmetzdavid Offline
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#1
Smile  Bosch M pump timing question
Hello everyone! I have a question, and could not find any answers, maybe someone knows: I have built my injection pump for my superturbodiesel by myself (changed the stock elements to dieselmeken's 7.5mm LF3 elements, added an outside adjustable alda built from a wastegate actuator, etc.) and had the pump adjusted by my local bosch diesel shop to 50cc full load no boost, 150cc full load at 1,5 bar of boost pressure. Did this more than a year ago, and since I had the pump installed to an engine at around 10 degrees ATDC but it seemed too advanced. Started hard and smoked unburnt fuel even at idle. As the pump was only adjusted by the diesel shop, and I guess they did not adjust the governor, it should have the standard timing like a stock pump? At what position of the engine should I try to make it work the best? Thanks.
02-02-2019, 11:13 AM
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NZScott Offline
HX30W 73/44mm
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#2
RE: Bosch M pump timing question
Unburnt fuel means it'll be too retarded. Honestly the best way is just to move it around until it feels right. That's how I've timed my 7.5mm pump, have no clue how of the degrees but it seems happy...

With fatter elements you'll be injecting fuel faster, so it doesn't need to be as advanced as with a stock pump. In theory...

1978 300D, 373,000km
OM617.912 with a Holset HX30W, 7.5mm IP, 711.113 5 speed (awaiting certification to be legal...)

1977 250 270,000km (parts car)
1977 300D (ex 280) 500,000km 'new' DD





02-02-2019, 03:32 PM
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Petar Offline
7.5mm M pump
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#3
RE: Bosch M pump timing question
IF the timing pin on the governor hasn't been moved then 10 ATDC is too advanced, even with stock elements, let alone with 7.5mm. Remember that this is timing after TDC, not before. The lower the number the more advanced timing is.
Stock is 14 degrees, with 7.5mm try 16-20 degrees.
02-02-2019, 07:38 PM
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mmetzdavid Offline
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#4
RE: Bosch M pump timing question
Thanks for the answers, I will then put it to 20 ATDC with the fine adjuster at maxinum retardation, and will slowly advance it until it seems to find a sweet spot.
02-03-2019, 02:32 AM
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firen456 Offline
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#5
RE: Bosch M pump timing question
Hi,

just do drip method (google for it, I will not explain it) at 16-20 deg BTDC. I will suggest u'll try 18deg and move it till it runs well.
02-03-2019, 02:35 AM
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mmetzdavid Offline
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#6
RE: Bosch M pump timing question
(02-03-2019, 02:35 AM)firen456 Wrote: Hi,

just do drip method (google for it, I will not explain it) at 16-20 deg BTDC. I will suggest u'll try 18deg and move it till it runs well.

16-20deg BTDC? Not ATDC?
02-04-2019, 04:10 AM
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firen456 Offline
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#7
RE: Bosch M pump timing question
BTDC for sure. You will never have a SOI ATDC on our prechamber engines.
(This post was last modified: 02-04-2019, 09:09 AM by firen456.)
02-04-2019, 09:08 AM
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Petar Offline
7.5mm M pump
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#8
RE: Bosch M pump timing question
Note that the timing pin in the pump has little to do with actual injection timing. With the timing pin timing is 14 after TDC, but that timing pin could be set anywhere depending on how the pump builder built the pump, the flyweight carrier can be rotated. Why Mercedes decided to use 14 ATDC is beyond me, it could be any arbitrary number.

With the drip timing on the other hand you can see where actual start of injection is if you don't know how the pump builder set the pump. It is more involved though.
I agree with firen456 that the timing should be 16-20 deg Before TDC. Stock is 24 deg BTDC AFAIK, with bigger elements you want to go slightly retarded.
Search google for W115/om616 injection timing, there is a peachparts thread explaining drip timing in detail. Note that you will need the 31 tooth delivery valve socket to remove the delivery valve, as well as a manual inline primer pump retrofitted. Pay attention to delivery valve torque spec when you tighten it, the pump is quite delicate.

https://www.youtube.com/watch?v=neukRJ4olz0

In my opinion i would only do the drip method if i couldn't find the sweet spot with the standard timing pin method.
02-04-2019, 12:45 PM
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mmetzdavid Offline
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#9
RE: Bosch M pump timing question
(02-04-2019, 12:45 PM)Petar Wrote: Note that the timing pin in the pump has little to do with actual injection timing. With the timing pin timing is 14 after TDC, but that timing pin could be set anywhere depending on how the pump builder built the pump, the flyweight carrier can be rotated. Why Mercedes decided to use 14 ATDC is beyond me, it could be any arbitrary number.

With the drip timing on the other hand you can see where actual start of injection is if you don't know how the pump builder set the pump. It is more involved though.
I agree with firen456 that the timing should be 16-20 deg Before TDC. Stock is 24 deg BTDC AFAIK, with bigger elements you want to go slightly retarded.
Search google for W115/om616 injection timing, there is a peachparts thread explaining drip timing in detail. Note that you will need the 31 tooth delivery valve socket to remove the delivery valve, as well as a manual inline primer pump retrofitted. Pay attention to delivery valve torque spec when you tighten it, the pump is quite delicate.

https://www.youtube.com/watch?v=neukRJ4olz0

In my opinion i would only do the drip method if i couldn't find the sweet spot with the standard timing pin method.

Thanks alot, that's how I'll do it then. I built the pump, so the timing pin should be where mercedes put it. The bosch diesel shop only calibrated it between elements, at least that's what I asked. So I already have the delivery valve tool (welded 4 or 5 delivery valve holders one on top of the other and a handle). But I will then try the dripping method to make sure it is spot on. Thanks guys!
02-04-2019, 10:44 PM
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barrote Offline
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#10
RE: Bosch M pump timing question
Hum hum ... u probably have 2 problems ....
How did u checked cylinder phasing?
How did u checked SOI?
What changes have u done in the governor, well the governor can handle a lot , but most probably it is not stable...
Did u know that M pumps in benzes are known to work 180° ofset?
I guess now u have problem in hands...but start by checking SOI ... it must be between 22 and 24 btdc.
Drip method or timing light ...
FD,
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02-07-2019, 06:31 PM
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