Crankcase vent

Bottom End (cases and crankshaft)
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65 Eric
Posts: 47
Joined: Fri Jul 13, 2007 10:35 am

Crankcase vent


Post by 65 Eric » Fri Oct 19, 2007 8:09 pm

Description: Hey everyone, been putting together a 65 pan, my first, and don't know what this oil line is for

Hey everyone, been putting together a 65 pan, my first, and don't know what this oil line is for. It's at the bottom of the right side of the case and inboard of the oil pump. Guy at the dealer told me to plug it, doesn't sound right to me. Is this the line that dumps oil if your oil pump check valve is leaking (sumping)? I learned about that here, you guys have been a big help, appreciate any info on this. By the way, my Clymers manual is no help here, no oil diagrams.


Post by fourthgear on Sept 19, 2006, 5:03pm

Sounds like the vent/breather line to the oil tank and since you have a 65 (electric start w/ alum. primary)there should be a " T " fitting in there that branches from that vent /breather line to a nipple on the inner primary( middle of inner primary), hoses are used to connect them all . Unless you are running a belt drive or closed and filled primary , I would not plug the vent line , it is supposed to help the oiling and scavenging of the primary chain drive system, not to mention venting of the motor.

Post by 65 Eric on Sept 19, 2006, 6:06pm

Thanks Fourthgear, I forgot to mention I installed an open belt, it had a wet clutch before. Should I run a hose to ground?

Post by Cotten on Sept 20, 2006, 1:33pm


I believe that the line that you refer to is indeed the oil return from the bottom rear of the primary case.

(The breather is a simple 3/8" metal downtube aimed at the ground, and is tapped into the cast-in breather gallery on the flywheel portion of the case with a large fitting that is captured upon the tube.)

The nipple fitting for the return line is a very long one, as it is difficult to install a short fitting behind the pump. The usual way to plug the line is to tap the end of this long fitting for a set screw.


Post by 65 Eric on Sept 20, 2006, 3:44pm

Thank you Cotten and Fourthgear, it is a long 3/8 tube captured in a 3/4 fitting. The tube itself must seal against a seat in the case. I'll use a fine thread set screw of the appropriate size. This site is amazing, (thanks Panhead) there must be over a thousand years of combined experience here. Don't know a lot about Panheads (yet) but if I can help anyone with machining issues (been a Toolmaker for a few decades) feel free to ask.


Post by mtnspan on Sept 20, 2006, 6:05pm

If you would like to see how mine is plumbed send me a pm. I'd be glad to help ya!
Bob in San Dimas

Post by fourthgear on Sept 22, 2006, 12:50pm

Post a photo here if you can for all to see and for reference later if ya can.

Post by mtnspan on Sept 22, 2006, 9:54pm

Fourthgear, I'll try to get a pic, but I think Eric is asking about the vent line from the case to the oil tank. (upper fitting next to oil pump) The lower fitting would be the breather vent which on mine has a small filter attached.

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