Don't know if this is good or not but running it by you guys .
This only happened once. Went for a short ride and looked dn to see my oil filler cap had popped off and was sitting loosely on top of filler hole.
Rubber seal seems to be tight on cap but the pressure seems to be high..
No hot rodding at all when it happened.
Has not done it again but pressure seems high in the oil tank..??

 

Is your oil level higher than the bottom of the weld on the filler tube? If you have too much oil in the tank it will cover the vent and cause pressure build up.


Also check the breather hose for kinks.

 

Made sure hoses were open and I run my oil slightly lower than full mark

 

Happened to a friend of mine. Turned out to be a broken piston ring causing excessive crankcase pressure to build. If tank pressure "seems high", it must be coming from somewhere. I'd perform a leak down test and see what it tells me.

Its happened to me a couple of times, but it's always been a shrunken filler plug. A new plug fixed it.

 

This only happens when you vent your heads to atmosphere and not to the carb like the EPA wants you to!!!!

 

Well you ought to know your head been vented since you were born😁

 

New engine so doubt rings.

 

we have had new pistons with the ring lands that do Not have the right spacing for the rings and they stick an wont let go

do a leak down test dry then wet

 

Follow up on oil tank pressure and oil cap being pushed off. Not that anyone cares but awh well.
I ran 2 - 3/8 ID gas lines, one off each head breather. Ran them both up and over the heads and under main frame, then down and out by the rear swingarm and pointed out past rear tire. Seems to be doing well and the oil cap stays in place. Problem solved.

 

This sorta happened to me. When the plug pops out, does oil come with it? Mine was pumping primary oil in to the engine or the engine was sucking it out of the primary. If this is true check primary oil level to see if it is low. I have seen a couple of threads about this type of trouble.

Good Luck
Doug