SBC Oil Pump Question

[ScotI]

I swapped an oil pump from one engine (sbc) to another. It’s a stock style Melling pump w/stock style pick-up that was new/no miles.

I ‘pre-assembled’ the top end of the ‘new’ motor. I was trial fitting various brackets & air cleaner on the intake, & needed to install the distributor. In order to seat the distributor, I had to rotate the oil pump shaft slightly & that’s when I noticed what I perceive to be a possible problem.

The pump has inconsistent resistance when you are spinning it. It feels like it might be binding but then it will spin freely. In all honesty, I’ve never verified the operation of an oil pump so I’m not sure what I should expect. The engine did not have oil in the pan, so the pump was spinning 'dry' when I noticed this issue.

Does this seem normal?

[Davezz28]

Oil pumps are cheep, just replace it. You don't want a $30 part destroying the entire engine.

[ScotI]

Oil pumps are cheep, just replace it. You don't want a $30 part destroying the entire engine.

I would rather understand whether the issue I described will be a problem by learning more about how they work. What if I were to get another & it did the same thing? That wouldn't necessarily mean it's normal, it could mean I got another bad one.

But . . .... Good logic. $30 is cheap insurance.

[myclone]

The pump should sping freely with no "tight spots" if its dry. Could be a warped pump cover, machining swarf that wasnt fully cleaned out during manufacturing, or any number of things. You could take it apart and dress the flat machined surfaces using ~2k grit paper, clean out the swarf, or fix whatever is wrong with it and be fine. However, like was mentioned above they are cheap so is it really worth your time to "fix" a new pump or is it better to throw it in the "use for cheap rebuild" pile and pick up another pump.

If it were me Id disassemble it, clean it thoroughly, and put it back togeather to see if its still sticky. If it is Id pitch it but if cleaning it fixed it Id use it.

[ScotI]

....However, like was mentioned above they are cheap so is it really worth your time to "fix" a new pump or is it better to throw it in the "use for cheap rebuild" pile and pick up another pump.

That's the pile it came from because this is the 'budget-special'. I guess I'll purchase a new one.

Thanks guys!

[Davezz28]

It may be the way the PU was installed. The pumps are made out of cast iron and if it was clamped into a vice to beat the PU on, it can actually bend the cast and cause a tight spot when the gear goes by the dented area.

Take the pump apart and look to see if there is a shiny spot on the edge of the gears or a spot inside the pump that show where the gear was rubbing the pump body.

If the PU was welded on, they may have got too much heat in the pump and warped the cover or some other part.

You may be able to determine what is causing the tight spot, but the pump should be replaced.

[ScotI]

On the first motor, the pick-up was just pressed in.

When I swapped it over to the 'new' motor, I used one of those Moroso straps that secure the pick-up w/o the possible heat distortion from welding.