is there anyone that can tell me the difference of the 2a4424/8m9760 and the 1p3409 pump that i am told is the replacement for the 2U pump

22B

Hi 22B,
purely of the top of my head after looking--NPR would give relevant Service Magazine articles relating to your query.

First would be change from Castellated Nut holding the Tall older unit together on to the later Forged body pumps with a bleed screw.

Later Forged Body pumps without bleed screw.

Somewhere in there would be a quiet idle cut on the Low Idle side of the Plunger Helix dump channel, see scan below from a Service Magazine Dated :- June 20 1949 on the D397 engines.
Articles I found told of the Pusher D8 having a fuel system with characteristics of the units used on the D386 engine which are the predecessors of the D397 units.

I feel I read about this quiet idle cut that may have first been applied to D2 type engines for a more stable Low Idle and seem to have spread across the range.
I will keep looking for more on this.

Changes beyond these to the 1P numbers I am not personally aware of--someone else or said Serv. Mag. articles or such from the NPR supersessions may tell more and if said 1P units, or indeed any of the other P/No units, need to be installed as a full set or not to save rough running at lower or other speeds.

I stand to be corrected.

Cheers,
Eddie B.

Hi John,
interesting your comment about the broken cranks in early D2's.

I have yet to research this Cut further but, I do recall it was also for maybe a RPM hunting issue at low idle in the small engines, other than this until I can maybe find an article here on it I am guessing and working with a hazy recollection from my time in the Injection Pump Shop at the Dealer.

Lightly loaded small Diesel engines require very little fuel to idle and I can see in my mind that the course type of governors used on early engines would be hard pressed to achieve a stable Low Idle speed without the cut or some form of modification to the Helix profile that would likely be less effective due to the Governor's limitations.

Cheers,
Eddie B.

"22B" wrote:

is there anyone that can tell me the difference of the 2a4424/8m9760 and the 1p3409 pump that i am told is the replacement for the 2U pump

22B

They are all 10mm forged body pumps.
2A4424 is the same as 8M9760
1P3409=5M7577=7M9870=8M2899 and require a 7M7435 spacer under the pump for D339, D342, D7 and D8 applications.