Ironhead Oil switch light comes on after short ride

[staniel]

Originally Posted by Ferrous Head

No, gravity will ensure oil comes out if the switch fitting is removed. It's how we prime the pump after an engine rebuild.

This is a little confusing to me. You don't rely on gravity to prime the pump. To prime the pump, you have to turn the engine over to push oil thru the pump with the switch removed to displace whatever volume of air might be in the lines. This is what I did when I removed the switch the other day to confirm the pump was working.

If my pump wasn't working, oil shouldn't have spit out when I removed the switch and kicked the engine over because the gerotors wouldn't be "pumping," right?

[staniel]

Originally Posted by toodogs

1 atmosphere is ~14 psi. a conventional pressure gage at 0 takes the atmospheric pressure into account, the 3 psi gage is in addition to the atmospheric pressure.

Lol you're right... I had a little bit of a brain fart

[ryder rick]

You are confusing absolutely and differential pressures.

No a loose vent hose will not make the light come on.

The switch is likely out of range.

[needspeed]

To your question: could it be a bad switch? From a recent thread with a similar issue it appears that the switch function can vary between brands.

Good info at post 11.
http://xlforum.net/forums/showthread.php?t=2081474

If you can't find the problem, a switch swap might be tried. At least they're inexpensive and easy to put on.

Not important but just a note. Your '72 doesn't have gerotors. It pumps with spur gears.

[ryder rick]

20w50 or 60W?

[Ferrous Head]

This is a little confusing to me. You don't rely on gravity to prime the pump.

Well, I do.

The oil light switch is fed by a very small hole. You may have a partial blockage there or the switch may be faulty.

I remove the switch and leave the bike over night. In the morning you will find a small puddle of oil in your drip tray. You have allowed enough time for the oil to displace any air pockets in the system.
I then replace the switch and remove an oil line at the bottom of a rocker box. I then kick/turn the engine over until I see oil flowing from there. Replace the screw

I then remove an allen screw (grub screw) from the front rocker box. And I check for oil flo there.

If that's all good I continue kicking until oil flows from the return line into the tank.

This takes an average of 66 kicks on a fresh engine. So, be patient.

This procedure does not confirm that oil is flowing through the crank but it's easy enough to do.

Gravity does allow oil to flow down through the line and the pump. This is exactly why most early Ironheads wet sump.

[staniel]

Originally Posted by Ferrous Head

I remove the switch and leave the bike over night. In the morning you will find a small puddle of oil in your drip tray. You have allowed enough time for the oil to displace any air pockets in the system.

Maybe I'm getting hung up on terminology here, but gravity can't displace the air in the system if you aren't pushing the air thru (i.e. turning the engine/pump over). Priming an oil pump is similar to bleeding brakes in that they have the same intent: remove any air in the system. Or maybe I'm misunderstanding it at that level.

Idk! In any case, I'll do those checks that you stepped thru just for peace of mind, but it makes sense to me that if I have oil returning to the tank, my pump should be working.

The light was off when I started the bike last night, but I haven't had a chance to give it a test ride.

[brucstoudt]

gravity is pushing the air out of the oil lines.the same way gravity wet sumps your cam chest over the winter when it sit's idle.it's a known occurence,it's not heresay.

[Ferrous Head]

In fact you aren't "pushing" the oil. With gravity it "pulls' the oil down.

In the same way your gas tank works. There is no air pressure differential between your gas tank and your float bowel.

Oil pumps are designed to pump oil. If the oil pump has oil in it, it will create a suction on the inlet side. This is because it will move more oil than gravity can provide when the pump is not working. But if the pump only has air inside it the suction effect is simply not there.

This is why we "prime" the oil pump. Initially filling it with oil so that it's providing the suction to pull in more oil.

We just remove the switch to allow the air inside the pump to leave the system. That allows gravity to do it's job. Gravity will provide about 2-3 PSI in our case to pull the oil through the system.

I bleed the brakes on my Corvette the same way. Gravity. It works. It takes longer than using a vacuum bleeder and it is faster if you have someone else helping you by forcing the fluid by pumping on the brakes. But gravity does work if you work on your own.

[Ferrous Head]

Oh !

No need to do the other checks if you have oil returning to the oil bag. It's what I do on an engine I've had apart.

gravity is pushing the air out of the oil lines.the same way gravity wet sumps your cam chest over the winter when it sit's idle.it's a known occurence,it's not heresay.

Bruce is right on the money. These pumps have a basic design flaw. The drive shaft for the pump has an oil seal in the body, between the feed and return sections of the pump. But none on the top side of the feed section where the drive shaft exits the pump.
This will ultimately allow oil to escape from the pump.
Rather than address this problem HD decided it was a non issue as when the bike is ridden regularly the return system will "fix' the problem. They did add a transfer valve to allow a large volume of oil to pass into the primary side "just in case".

I have no idea why they just didn't add a seal on that shaft.

I have a thread on here somewhere that shows you how to do this yourself if your so inclined. (But you have to remove the pump to do it and HD did not design this bike with a provision to remove an oil pump with the engine in the frame). Another design flaw ?