Oil Pump Seal

Classic short-frame models

Oil Pump Seal

Postby Otis » Wed Oct 16, 2019 8:19 am

Logic would have it that the open side of the oil pump seal 26227-58 would face towards the scavenger gear where the oil is but a reputable engine builder told me the open end faces up towards the engine when the pump is mounted putting it against the pump body. Can some please clarify this for me. I’ve always been told the open end of any seal faces the oil or grease it’s containing.
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Re: Oil Pump Seal

Postby Lisa » Wed Oct 16, 2019 9:13 am

When installing seal in the pump gear housing the lip is facing down flat up - in the inner cover it is the opposite lip up flat down. If you don't use a modified inner cover with seal your pump will in fact wet sump over time. Just a word to the wise. And this is the PROPER way the seals go in no matter what anybody else says.
Last edited by Lisa on Wed Oct 16, 2019 5:00 pm, edited 1 time in total.
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Re: Oil Pump Seal

Postby Ferrous_Head » Wed Oct 16, 2019 4:22 pm

Your correct in your belief. Normally the lip does face towards whatever your trying to contain. In a situation where pressure on the oil/grease side is higher than atmospheric pressure the lip design helps use that pressure to seal.
If you install them "backwards" oil/grease is liable to leak.
In a situation where the seal allows the oil/grease to leak out of the case/housing that's an obvious problem. Who wants oil dribbling out of their gearcase ?
If the seal in the pump body was totally missing what would happen ?
In fact, not a lot. Some oil could migrate into the feed gear area. Which is full of oil anyway.

With the inner cover if you install the seal "backwards" it might allow some oil to migrate into the tower area when under pressure. ie when the engine is running.
But that would never be a real problem as long as the engine is running.
When the engine is stopped the pressure will drop and I suspect the seal would still hold well enough to stop the engine from wet sumping. Certainly it has to be better than no seal at all. Harley's design.
"I know only too well the evil that I propose, but my inclinations get the better of me."
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Re: Oil Pump Seal

Postby Lisa » Wed Oct 16, 2019 5:08 pm

If there was NO seal in the gear housing the oil will weep through the shaft to the return gears and in fact over time wet sump right through the return system all your oil in the oil tank to the lower end just like the breather gear shaft. OH almost forgot about the valve and or ball seat they half to be perfect also with no air pit 's from a cast or an inferior seat product.
FACT all half to be sealed or you will in fact HAVE a wet sumper that you can enjoy. LOL = don't put a seal on a door and you end up with a air leak amount will very ? Same thing....
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Re: Oil Pump Seal

Postby Otis » Wed Oct 16, 2019 6:12 pm

So just to clarify. The lip (as you and my service manual call it) faces upward towards the feed gears, not downward towards the scavenger gears?
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Re: Oil Pump Seal

Postby Lisa » Wed Oct 16, 2019 7:43 pm

Put the pump on the table put the seal in the hole lip down and push down in done deal done right flat facing you lip down. If your pump housing doesn't have a cut out for a seal have it machined for one because without it the pump will in fact wet sump through the shaft to the return gears and into the lower end over time. On the inner cover seal lip up flat down opposite of the housing seal. This is the proper way the seals go in. OH if you don't put an inner cover with a seal in it watch it wet sump over time. FACT from experience.
Last edited by Lisa on Wed Oct 16, 2019 9:51 pm, edited 1 time in total.
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Re: Oil Pump Seal

Postby Ferrous_Head » Wed Oct 16, 2019 8:57 pm

As per the FSM.

"Install seal carefully over shaft, with lip side facing pump body."


This may sound counter intuitive. But while the scavenge side gears are bigger the return side has less pressure in it than the feed side. And it's the pressure that would determine which way the oil flowed around the shaft.

I have had a lot of engines which didn't wet sump. It is fairly clear to me that the clearance between the shaft and the inner cover is the critical point. When new these clearances MAY be tighter. It might just be production tolerances. For a long time I thought it might depend on whether the engine when stopped cam to rest with the breather valve open, or closed.

if I have an engine out of the frame now I would do the modification. The costs are minimal, (last two I had done cost me about $50 each including the seal ($95 on Ebay).
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