Can oil pump be bench tested?

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Hi all,

This is an interesting thread. The french article OP found old pump bodies to be out of alignment. This was an eye opener. Anyone wanting to improve his/her oil pump by lapping should check faces for trueness first.


-Knut
 
Carl H said:
Dans le sud des États-Unis, ils ont des insectes qui font des nids avec de la boue dans des trous, comme des tuyaux d’évacuation de réservoir d’essence. J’ai eu un problème avec un insecte qui est entré dans certains corps de glucides NOS et a laissé de la merde dans le circuit de carburant inactif. Et j’habite dans le nord du Massachusetts.
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Nous avons aussi des insectes comme ça dans le sud de la France. ;)
 
NickZ said:
I ran the tests on all 4 pumps.
Test Conditions:Castrol SAE 20W-50 used engine oil (300 miles), 70* F; 0.100" Flow Restrictor.
For the feed side testing, all 4 pumps exhibited a pretty much linear relationship between pump rpm and pressure over the range of rpm used. The figure of merit I used for comparison of the feed side performance of the pumps was the pressure at 5000rpm equivalent engine speed. Again my original pump performed best, at just over 70psi. The next one was about 68psi and the other 2 between 63 & 64psi.

For the return side testing, I ran the pumps at the equivalent of 2600rpm engine speed. The pump from the '73 750 engine performed best with flow rate measured at 0.536 liters/minute. My original pump came next at 0.484 liters/minute. Next was the other '71 pump at 0.366 liters/minute. The pump from the '73 850 engine had no return function.. It didn't move any oil out of the container at any pump rpm.

So what do I conclude from all this?
I feel comfortable just putting the original pump back in the engine and leave it at that. It has the overall best comparative performance. There is only a very small amount of end play (0.0015") on its shaft, so I'm not convinced there would be any benefit to disassembling it and lapping the surfaces.

Sounds like all this test rig building & testing was a waste of time... but no. I'm really glad I did this testing instead of just replacing the original pump with the now known to be non-functional spare (which came from the 850 parts) as I had seriously considered doing (see my original post).
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Really nice test bench setup and i sure appreciate the good data. Ive been doing some bench testing too and will share more data later when i get things a bit more sorted out. But ive noticed thatthe scavenge pump performance is very
sensitive to inlet side restriction. Its 60% more capacity than the feed side pump but it cant do squat with inlet restriction. It cavitates easily. So i checked the longest segment of the inlet path on the bike and its the 4.75” drilled hole passage from sump drain plug hole to the sharp turn upward where it meets the 1.75 drilled hole up to the turn into the pump. Anyway that 4.75” run is only a 3/16” dia. QUES: ever heard of anybody drilling it out to 7/32”???
I just drilled mine out to 13/64 but of course am concerned about pressing my luck to go any bigger. The resistance to flow varies with the fourth power of the inner diameter. So a 3/16 ID for example would have over 3 times the resistance
as a 1/4” ID hole of same length.
Thks for whatever comment u can provide, TomV
 
Tom Vachon said:
Really nice test bench setup and i sure appreciate the good data. Ive been doing some bench testing too and will share more data later when i get things a bit more sorted out. But ive noticed thatthe scavenge pump performance is very
sensitive to inlet side restriction. Its 60% more capacity than the feed side pump but it cant do squat with inlet restriction. It cavitates easily. So i checked the longest segment of the inlet path on the bike and its the 4.75” drilled hole passage from sump drain plug hole to the sharp turn upward where it meets the 1.75 drilled hole up to the turn into the pump. Anyway that 4.75” run is only a 3/16” dia. QUES: ever heard of anybody drilling it out to 7/32”???
I just drilled mine out to 13/64 but of course am concerned about pressing my luck to go any bigger. The resistance to flow varies with the fourth power of the inner diameter. So a 3/16 ID for example would have over 3 times the resistance
as a 1/4” ID hole of same length.
Thks for whatever comment u can provide, TomV
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showing my failure to remember what I was taught in hydraulics/fluidics way back when - 1972 ?? -
but I do remember that increasing diameter decreases pressure and decreasing diameter increases pressure on the column of liquid that is being pushed . I seem to recall that it is easier for a pump to push than it is to pull but I forget the whys and the effect of changing the diameter of the inlet path regarding pressure / flow. I get the resistance bit but very foggy on the rest . Presumably the length of the tract has an effect at least from a friction standpoint and also on flow as for a given diameter the longer the tract the more mass has to be pulled. I know this is not much help and I would like to understand again what I think I understood 50 years ago.
 
It depends on the type of pump as to whether it pushes better than it pulls and a positive displacement gear pump is a type that does push better than pull. The pump in your washing machine or dishwasher pulls well but you can block the outlet easily with your hand and is a centrifugal pump.
 
Richard Tool said:
showing my failure to remember what I was taught in hydraulics/fluidics way back when - 1972 ?? -
but I do remember that increasing diameter decreases pressure and decreasing diameter increases pressure on the column of liquid that is being pushed . I seem to recall that it is easier for a pump to push than it is to pull but I forget the whys and the effect of changing the diameter of the inlet path regarding pressure / flow. I get the resistance bit but very foggy on the rest . Presumably the length of the tract has an effect at least from a friction standpoint and also on flow as for a given diameter the longer the tract the more mass has to be pulled. I know this is not much help and I would like to understand again what I think I understood 50 years ago.
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The resistance to flow is directly proportional to the length of pipe, tube, passage and directly proportional to the amount of flow. But its inversely proportional to the diameter to the fourth power. Bear in mind that as the diametr increases the cross sectional area for flow increases by the square and then add to it the friction and viscous effects that also increase by the square so it ends up to the fourth power. So a diameter 1/2 the size creates 16 times more resistance to flow! Kinda hard to fathom but thats what it is, all else being equal.
Anyway thats why im enlarging that 4.75” drilled hole that runs from the sump drain plug hole dver to the vertical drilled hole that goes to the scavenge pump.
Its only 3/16” diameter. Dont know why they made it less than say 0.25” since the pump is sensitive to inlet restriction, especially at high rpm whete it seems hard for the inlet side to keep up. I never had the cases apart to get an idea of how much extra, if any, stock is around that drilled hole. This is all kinda preliminary for me and i’ll let u eventually know where i end up with everything. In the meantime does anybody know if others enlarged that 4.75” long drilled hole?.
thks, and Merry Christmas! TomV
 
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