Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties Puking oil from crankcase breather

Puking oil from crankcase breather

Post Mon Mar 15, 2021 2:00 pm

Posts: 42
I have been riding my UL around the neighborhood to get the last few bugs worked out. I have been having luck getting everything all sorted except for one thing

Oil is puking out of the crankcase breather on the cam cover.

I replaced the flutter valve a while back. I'm running the CHP pumps and the breather is timed correctly AFAIK.

What is causing this?

I'm not talking about it leaking a bit on startup like these tend to do.

I mean, it leaks little to no oil on startup, and the more the motor is run, the more oil is puking from the crankcase breather on the cam cover. Riding it down the road, it is gushing oil from the breather, all over the side of the motor, exhaust, frame etc.

Post Mon Mar 15, 2021 6:02 pm

Posts: 606
Location: Spokane WA USA
Maybe reading this post will give You an Idea.

Post Mon Mar 15, 2021 7:53 pm

Posts: 42
Yeah, I have read through that a few times actually.

I have emailed Carl at CHP, and he has told me to check and make sure the breather gear is timed correctly, and, to make sure the generator has the oil separator gear installed on it.

(I didn't know there was an oil separator gear on the generator!!)

I'll be pulling the cam cover to check those things soon.

I also suspect the flutter valve...... Will check that too.

Carl mentions in there how he added a secondary scavenging system to work with the scavenge pump. I need to ask him about that for more info. But I think that was just to reduce the amount of power robbing oil that is in the crankcase acting like brake as he put it. He didn't mention anything about puking oil from the breather...... I wonder if that secondary scavenging setup he details there was done ALSO for the purpose of preventing oil from puking from the breather?

Post Sat Mar 20, 2021 7:53 pm

Posts: 606
Location: Spokane WA USA
"I didn't know there was an oil separator gear on the generator!!"

When You pull the cam cover, Check the Football shaped spring loaded contact plate that contacts the slinger gear face end of the generator, Make sure it is not binding. Hopefully the generator has a slinger gear.

If all is well there Follow elsewere.

Post Thu Mar 25, 2021 1:55 pm

Posts: 42
Thanks Don,


I really don't know what I'm looking for regarding the oil separator. Is it that round disc behind the drive gear?
Does this generator look like it's setup right?
I'm not seeing a football shaped plate? Or maybe I'm just dumb. :shock:




These pictures show how I'm timing the breather. Using a set of calipers to push the gears in and hold them the specified distance from the case mating surface where the cover goes.

I've stuck a screwdriver in the breather timing hole for a visual aid.


My flutter valve seems to be broken...... I got it on Flea-bay from a guy named Yor-mario on there. Or something like that. When I got it and installed it, I could both SUCK and BLOW air through the flutter valve. I asked the seller about this and he said "They work on vacuum from the motor. Need to have installed and motor running to work".......

Now I can't suck OR blow air through the flutter valve. My understanding is you should only be able to suck air through the flutter valve but not blow air through. IS THERE NOT A BETTER TEST THAN THIS?!?!

When I pulled the cam cover there was quite a bit of oil in there. There shouldn't be very much in there if the flutter valve is working correctly should there?

Post Thu Mar 25, 2021 5:02 pm

Posts: 606
Location: Spokane WA USA
"Does this generator look like it's setup right?"
No! You have a Knuck/Pan gear on the gen. end.
This is what it looks like: ... XQxj1R7ZK0

The face of the slinger mates up with that floating "football shaped" piece on the cam cover, That leads to the breather tube to atmosphere. "the ground".

Inside the cam cover: ... SwiwdeI98f

I cannot believe the insane prices! I would buy factory stamped / matching cases for under $100.00
Sorry i am giving away My age.

Flutter valve, Spray clean out carbon, clear passages, It is just a triangaular piece of metal used to block pressure/vacuum Hence "Flutter"

Post Thu Mar 25, 2021 8:15 pm

Posts: 42

Thanks for all your help thus far :D

This gen is a Cycle Electric unit , 12 volt. It has been on the bike for 20 years, and when the bike was last running it never presented a problem so I think it must be ok?

I found some information on another forum regarding this generator.

"From Cycle Electric:

The two brush and three brush generators use different oil deflectors. The oil deflector prevents too much oil from getting on the ball bearing. On two brush models it also sets the location of the gear.

Since the gear is pined in place on the three brushes, the oil deflector has a spring between it and the bearing to hold it up against the gear.

The oil deflector used on two brush generators has a built in collar. The gear is drawn onto the shaft with a nut until it pinches the oil deflector tight against the inner race of the ball bearing. This sets the location of the gear and locks the armature in place.

When changing from a three brush to a two-brush generator do not use the old oil deflector and spring. Use Harley Davidson part #31035-58."

Post #4 here: ... p?t=212188


I also can't believe the ridiculous prices. Some of them are downright obscene.

I understand what you mean now! Yes that football shaped piece is in place on the cam cover I have here.

I definitely cannot suck any air through the flutter valve. This must be why it's puking oil from the breather tube?

The stupid thing is like I said, when I installed this flutter valve not that long ago, I could blow and suck air through it.

Post Fri Apr 09, 2021 11:31 am

Posts: 42
I installed a new flutter valve and it allows you to suck air but not blow air.

Hoping this was the main if not only reason why oil is puking from crankcase breather.


https://www.flatlandmotorcyclecompany.c ... -1639.html

Is this the correct setup to install an oil separator on this generator?

Post Fri Apr 09, 2021 5:55 pm

Posts: 606
Location: Spokane WA USA
"Is this the correct setup to install an oil separator on this generator?"

Post Mon Apr 12, 2021 11:25 am

Posts: 42
Thanks Don.

I emailed Flatland motorcycle company and they are telling me I need this slinger gear.

https://www.flatlandmotorcyclecompany.c ... t/?q=29143

I have asked them how the retaining pin and spring are installed but have yet to hear back from them...

Here is what my generator looks like with the pan/knuck gear removed.


The only thing holding that pan/knuck gear on was that nut...... I'm not sure if I can just use that same nut to attach the correct oil slinger gear..... There is no hole in the generator shaft for that retaining pin... And what about that spring??

So confused.

Post Tue Apr 20, 2021 6:22 pm

Posts: 606
Location: Spokane WA USA
If Your set up worked with out rubbing the cam cover inside, then I would say, install the slinger to cover the gen bearing, install the spring, install the slinger gear, and use a new lock nut to retain all.

All slinger gears including the sportster seem to work with the treaded end shaft with 4 splines and locknuts.
But! watch out! due to variations in 4 spline machining, You may need to space between the spring and gear.
the gear alignment is checked just prior to cam cover install.
I have only run 6V generators. Most do not have the threaded extension to the shaft except Police Gennys. early gears were pinned using a taper pin, or a spiral wound pin to retain the gear to shaft. or a lessor roll pin here.

Post Mon Aug 23, 2021 1:51 am

Posts: 42
I installed the correct generator gear, the one with the oil separator.

I also found that the football shaped spring loaded contact plate appeared to be stuck down in the cam cover and freely moving back and forth (What is the actual term for this football shaped piece?)

I removed it and purchased a new one. However, the pins that it installs with are too small. The pins press fit into the cam cover, but the pins supplied with the new piece are way to small to work, they just fall into the corresponding holes in the cam cover.

How does this piece work, and how are these pins supposed to be installed? Press fit I assume. Which won't work here so what's the course of action now?

I recently dragged home a discarded Craftsman 101 lathe. Making some pins of the correct size could be possible.

Also, I see cam covers on Fleabay that appear ready to go. May go that route.


These pins are what press into the cam cover. They are way smaller than the holes in the cam cover that they press into.


How much gap is there in between these two pieces typically?

Post Thu Aug 26, 2021 7:40 am

Posts: 3553
Location: Central Illinois, USA
Sorry for a late reply, WildOne,..

But I had hoped an expert would reply instead.

The brass 'separator seal ring' (25281-37) is spring-loaded (25287-37) so it will gently press upon the end face of the slinger (31071-37), traveling freely upon the dowels.

PS: I can't remember how it all works to separate the oil mist, but I do know the 25350-37 breather valve is critical.

Post Thu Mar 17, 2022 12:40 pm

Posts: 42
After checking and fixing everything else: verifying breather timing, flutter valve, cam cover seal ring, oil seperator gear... None of that did anything to stop the CHP feed pump from puking from the breather.

I finally did what Dick (Frankenstein) did where I tapped into the pressure regulation circuit.
(First post of page 2 here: viewtopic.php?f=12&t=12718&start=20)

Carl who makes the CHP feed pumps stopped responding to me. He wasn't very helpful throughout the process.

Here's some videos I made:

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