Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties Breather plumbing

Breather plumbing

Post Tue Aug 07, 2012 10:12 am

Posts: 543
Location: Wa, USA
I have read on several different forums that HD oil systems must have a sealed (not vented) oil tank to work correctly. This doesn't really make sense to me, so any info on this would be appreciated.

I am thinking of replacing the breather tube in the cam cover with a fitting and plumbing it into the tank to return the oil mist from the breather to the tank. This would require a non sealed tank with a breather screen type cap or some other way for the tank to breath. Anyone have any thoughts on this?

Post Wed Aug 08, 2012 5:33 am

Posts: 219
Location: Georgia
Didn't the original 45s have the oil tank alongside the gas tank and were vented?
F

Post Wed Aug 08, 2012 12:33 pm

Posts: 391
I am thinking of replacing the breather tube in the cam cover with a fitting and plumbing it into the tank to return the oil mist from the breather to the tank. This would require a non sealed tank with a breather screen type cap or some other way for the tank to breath. Anyone have any thoughts on this?

Thoughts? Yes, DON"T try it!
The oil tank is vented to the crankcase. This allows the oil to flow by gravity to the pump inlet. The system was never intended to be vented to the atmosphere. If you want to direct the oil mist from the breather somewhere just direct it to the rear chain as Shovelheads do, but not to the tank!

Didn't the original 45s have the oil tank alongside the gas tank and were vented?

Oil tanks on 45s were never vented.

Robbie

Post Thu Aug 09, 2012 12:57 pm

Posts: 543
Location: Wa, USA
Not trying to be a wiseass, but if the tank is vented to atmosphere, is gravity suspended? I ran my 45 for years with an oil cap that didn't seal as the result of an unfortunate incident involving a curb. It seeped a little oil, but the oiling system worked fine. I have read a lot of "don't do its" but the reasons do not really make sense. Gravity feed should work no matter what as long as the oil level is higher than the oil pump inlet and there is no vacuum lock in the tank which is what I always thought the vent was for. The tank being also vented to atmosphere should not affect gravity feed at all.

Post Thu Aug 09, 2012 8:48 pm

Posts: 391
Never mind, sorry to wast your time and mine! In the future I'll not bother!

Post Fri Aug 10, 2012 1:04 am

Posts: 543
Location: Wa, USA
Rubone;

I am not trying to denigrate your advice, only to understand. As I said, I have heard others say what you said. I am only looking for a more thorough explanation for why it doesn't work. If you could explain this further, I would appreciate it.

Post Fri Aug 10, 2012 9:54 pm

Posts: 1676
Location: Interlaken, NY USA

Woody, I plumbed Frankenstein to a BSA oil tank that had an atmospheric vent with no problems. Blanked off the vent line hole on the cases, and otherwise plumbed as normal. Never had a problem with the oiling or breathing system. That was many years ago. Also recently looked at a build by Paul Friebus of a big twin 80, with a much modified vent system. If I understood correctly, he streamlined the internal passage for the breather, and was running a 5/8-3/4" tube about 2 inches long instead of the original breather's opening.
Also, as a by the by, Frankie has no generator thus no oil slinger, and has never had any excess oil coming from the breather.
Just my personal observations, you understand....
DD

Post Sun Aug 12, 2012 11:37 pm

Posts: 543
Location: Wa, USA
Dr.
Thanks for the info. Your experience makes me inclined to give my plan a shot.

Post Mon Aug 13, 2012 5:22 pm

Posts: 67
Why?

Post Mon Aug 13, 2012 7:36 pm

Posts: 1676
Location: Interlaken, NY USA

Upon reflection, it occurs to me that the "closed" non vented system as featured on a stock machine isn't so closed. The tank vent line runs to the cam chest. The breather port connects directly to the cam chest, right? So, the tank is currently vented to atmospheric pressure via the vent line, cam chest, and through the present breather pipe, right? Looks like you're just coming up with another parallel connection from the cam chest to the oil tank, then to atmosphere. And a more direct one at that.
That would explain why I didn't have problems when I did it on Frankenstein,
DD

Post Tue Aug 14, 2012 9:21 am

Posts: 543
Location: Wa, USA
That is my thinking, also. I originally started thinking of a way to do this in order to eliminate the constant oil mist that bathes the front exhaust pipe under the engine. After a few years, it builds up a pretty good crust on the pipe and I wanted to try to get rid of it.

Post Tue Aug 14, 2012 11:42 am

Posts: 219
Location: Georgia
Woody
The timed breather system creates vacuum in the crankcase to evacuate oil out of it. If you vent the oil tank it can't create the vacuum. It may not evacuate oil from the crankcase correctly.

I modified my breather to a 1/8 NPT thread fitting and piped it back next to the rear wheel. What little mist mine creates goes on the road and back tire.
F

Post Tue Aug 14, 2012 5:11 pm

Posts: 1676
Location: Interlaken, NY USA

F, True the timed breather system does as you say, but that breather vent is the pump tower. It vents to the cam chest, which is not part of the area in which a vacuum is created. That area is roughly maintained at atmospheric pressure. Note the rush of air escaping when the timed breather vents the crankcase area.
DD


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