Fuel-lubed vs. Oil-lubed Injection Pumps

[rbattelle]

It is my understanding that the P7100 is lubricated primarily by engine oil. The VP-44 and CP-3 are both fuel lubricated only. It seems like the P7100 is significantly less prone to failure as a result of a failed low pressure fuel system.



So my question is - why did Cummins change from an oil lubricated pump to a fuel lubricated pump? I suppose "technically" it's somewhat simpler internally to just use the fluid you're pumping to provide lubrication.



But an oil-lubricated injection pump sure seems like it would cut down on all the VP-44 (and CP-3) failures from bad lift pumps.



Perhaps someone with more experience can shed some light on this...



-Ryan

 

[Joseph Donnelly]

The top end of the P 7100 is fuel lubricated. The other designs don't have the high rubbing forces of the P pump running lifters on cam lobes with heavy springs.

 

[nickleinonen]

and another potential problem with a engine lube oil lubed case on an injection pump and fuel lubed upper end is if you get any leakage past the plungers in the pump, that fuel leaking down will get into the lube oil... not too big of an issue, but still...

 

[rbattelle]

I didn't realize the P7100 is partially fuel-lubed. Now I understand the switch to a completely fuel-lubed pump.



-Ryan