Ironhead Oil Transfer Valve

FourCams · #1 17th August 2009

I've heard a lot of stuff about the mysterious oil transfer valve but couldn't find a thread that's dedicated specifically to it - so I'm starting one.
The transfer valve should be threaded into the case behind the primary cover and to the rear of the front primary chain (drive) sprocked.
It looks like this:

The oil transfer valve was used from 1957 - 1976. (OEM part number 25075-55.) It was discontinued in 1977.
I've been under the impression that it was put there to help keep the dry clutches from getting wet and it's designed so that oil will go from the primary to the engine if the primary oil level is too high. Does this sound right?
If the oil transfer valve is not blocked, oil from the primary can mix with oil in the engine. Some people plug the oil transfer valve and use ATF or other primary lubes in the primary/transmission. I'd be interested in seeing the different methods people have used to block off the oil transfer valve and what primary lube has been used after it's blocked. (Please don't turn this thread into an oil argument.)
If I understand correctly, the trans needs to be vented seperately if the oil transfer valve is blocked?
Anyhow, here it is.. the oil transfer valve thread.
Please share your oil transfer valve wisdom here.

BuckIRyder · #2 17th August 2009

Blocked mine off ('72CH) years ago. No ill effects seen. Pulled it out and a friend put a spot of weld in it. Its just as effective to pull the guts out and tap the hole and locktite a screw in. I did it because my primary was mysteriously filling with oil. Turned out to be a failed sprocket shaft seal. My motor sprocket was cracked thru the land that the seal rode on and that cut up the seal face. My trans vents thru a very small hole in the primary fill/inspection plug. And yes the trans needs to be vented somehow. I use 20/50 motorcycle synthetic as lube.

Ivan RoachCoach · #3 17th August 2009

...to either 8-32 or 10-32 thread-size (I forget which), thread in the appropriate screw slathered in red Loctite, and peen the screw head until it's distorted.

It'll never unscrew or back out of there --- EVER.

superwarden · #4 17th August 2009

Yep get rid of it if you like. Not much oil is ever "transferred" through it.

RRB · #5 17th August 2009

Quote:

Originally Posted by FourCams

I've been under the impression that it was put there to help keep the dry clutches from getting wet and it's designed so that oil will go from the primary to the engine if the primary oil level is too high. Does this sound right?

Doesn't sound right to me. I don't think it had anything to do with the clutch, as the plates were isolated behind the derby cover and "should" be impervious to the oil in the primary/trans. I don't think the intention of the valve was to keep the primary oil at a certain volume. I think the valve had more to do with crankcase pressure than with oil levels.

Quote:

Originally Posted by FourCams

If the oil transfer valve is not blocked, oil from the primary can mix with oil in the engine.

The problem is usually not oil from the primary migrating from the primary to the crankcase, but the other way around, at least in my experience.

Your thread is a good idea, though. I'm interested in what others have to say, too.

MDT · #6 17th August 2009

I just posted on another thread, it's a crankcase "breather". If oil splashes over to the primary side it is incidental. If you use the same oil in your tranny and your engine, it's not a problem. If you don't you should probably plug it. I don't plug mine.

FourCams · #7 17th August 2009

So... what exactly is the purpose of the oil transfer valve?
The primary vents through the oil filler plug doesn't it?
I'm reasonably certain (but not positive) that if the primary is overfilled the oil will go into the engine throught the transfer valve. I don't think it's supposed to allow oil from the engine into the primary though.

MDT · #8 17th August 2009

The pupose is to vent the pressure from the engine crankcase created by your pistons as they go up and down. As Mick stated in the other thread, oil transfer valve is not the proper term for this item. It was never intended to prevent too much oil in your primary.

FourCams · #9 17th August 2009

Quote:

Originally Posted by MDT

The pupose is to vent the pressure from the engine crankcase created by your pistons as they go up and down. As Mick stated in the other thread, oil transfer valve is not the proper term for this item. It was never intended to prevent too much oil in your primary.

Why would the crankcase vent into the primary? The crankcase has a breather on the oil pump and it vents through the cam chest doesn't it?

Are sure you're not talking about the "foo foo" valve?

If it's not the proper term, why would J&P, V-Twin, this forum, and every other Ironhead forum I've seen over the past 15 years refer to it as an oil transfer valve?
And why would the people who have plugged it not be having problems with engine seals if after they blocked it they vented the transmission and not the engine?
It makes more sense to me that it would vent from the primary into the crankcase - especially since there's a vacuum in the engine when the piston goes up and the crankcase breather is on the opposite side of the engine.

(I'm really confused)

Hopper · #10 18th August 2009

+1 on that. There is a whole crankcase breather system timed on the oil pump and venting out past the generator drive. That oil transfer valve, whatever its purpose, is not to control crankcase pressure. No way is the crankcase breathing into the primary, which then breathes to atmosphere through a pin hole in the filler cap.

Which way is valve set up to flow? If someone has a set of cases around, can they see if the valve is set to allow flow from the primary into the crankcases or vice versa?

I always assumed it allowed oil to flow from the primary back into the crankcase if the sprocket shaft seal was leaking.