Oil Tank Vent

[dwjohnson]

  I think this would pertain to or include the Big Twin oil tank vent system as well, but I'm working on an 95 XL.
     The small 1/4" or 5/16" hose that connects from the oil tank to the rear of the Sportster cam cover is the vent correct? But is it just an atmospheric vent for the oil tank to drain correctly or is it something more? I'm not sure why it is connected to the gearcase? Does the tank need or get pressure from the engine to force the oil to the pump? Is this just an EPA method not to vent the tank out to the open and to try to recirculate? Or is there a purpose for the air/vent from the gearcase or engine? Doesn't the engine actually breathe thru the top end air cleaner bolts and umbrella valves?  The reason I ask,  I want to do away with that hose from the tank to cam cover if possible, would you block off the cam cover fitting and just vent the oil tank to atmosphere? I plan on installing a big 1/2" vent out the top of cam cover. Assuming the oil doesn't slosh out of the tank thru that vent right? Or does the cam cover really need to connect to the tank, and why?
Thanks for any insight or thoughts.

[14Frisco]

The small 1/4" or 5/16" hose that connects from the oil tank to the rear of the Sportster cam cover is the vent correct? But is it just an atmospheric vent for the oil tank to drain correctly or is it something more? I'm not sure why it is connected to the gearcase?

It is the gear case vent hose - the gear case vents to the oil tank.

[Karl H.]

The oil tank is part of (and is interconnected to) the engine cavities (crank case, gear case) that are vented through the top end umbrella valves into the air cleaner. The oil tank must have the same pressure resp. vacuum as the other engine cavities.

Karl

[smoserx1]

I have two service manuals and both of them say

This crankcase breather connection provides
the pressure balance necessary for oil circulation.

There has been some discussion about this in at least one other thread recently, and one poster who's opinion I respect says it is ok to get rid of this connection (and seal each end) IF you vent the oil tank to the atmosphere with something like a vented filler cap or other means of venting the tank.  There have been lots of kits appear on the market lately to accomplish this, but I surely wouldn't just eliminate this vent and nothing else.  What if you end up with a vacuum in your oil tank that starves your pump and trashes your motor?  Engineers designed this vent for a reason. 

[dwjohnson]

 Yes all this sounds about like I was thinking. If I were to vent oil tank and gearcase independently to atmosphere, I think I should be fine. Is this the way everyone else see's it??  Thanks for the thoughts.

[Norton Commando]

Yes all this sounds about like I was thinking. If I were to vent oil tank and gearcase independently to atmosphere, I think I should be fine. Is this the way everyone else see's it??  Thanks for the thoughts.

That's the way I see it, too.

Jason

[Karl H.]

The engine case has a slight vacuum which is maintained by the umbrella valves. The oil tank should have the same pressure. Otherwise the oil flow gets compromised.

Karl

[Norton Commando]

The engine case has a slight vacuum which is maintained by the umbrella valves. The oil tank should have the same pressure. Otherwise the oil flow gets compromised.

Karl

So, if you apply vacuum to the oil tank, oil flow from tank to pump or from pump back to tank will not be compromised?

I guess I don't understand why there would be any impediment to oil flow with a positive displacement pump if the tank is vented to atmosphere.

Jason

Jason