Why is my oil cap/dipstick popping off when I put my Harely in gear after warming it up?

I have a 99 Harely Sportster and lately when I warm it up and begin to drive in 1st gear the oil cap/dipstick pops off causing oil to burst out. Is this a simple oil cap change or something else.Why is my oil cap/dipstick popping off when I put my Harely in gear after warming it up?
if this is an original stick, the gromet might have outlived its usefulness. if u look, the stick has 2 slots to line up in the oil tank. its alot easier to get the stick in right and be able to get it in nice and tight. i know that getting the dipstick in can be a real pita by experience.Why is my oil cap/dipstick popping off when I put my Harely in gear after warming it up?
bad grommet, oil fill to high, crank case pressure due to worn engine or relief is clogged
Because its a Harley.
This is a problem which in not unknown in Sportsters, just unusual. The normal cause is the oil tank vent line which runs from the top of the oil tank, down to the engine case, is routed under the electric starter, and get pinched shut. As soon as the engine speed picks up a bit, the tank cap pops out. Have seen this one a half dozen times, in the past 20 years, has happened ever since Sportys got electric starters.








Tomcotexas
It could be a couple of things. If you're bike has high mileage, you could be getting a lot of piston blow-by causing your crankcase to be over pressurized, blowing out your cap. Your crank case vent may be faulty or plugged, check a manual. If your motor is high HP, you may be just putting too much pressure into the crankcase. Or like the other guy said, your ';O'; ringed dipstick is worn out or you have too much oil in it.
Im guessing thats what happens when you buy American....although, Im not sure if they make Harely's in America........ I know HARLEYS are made in America though....





Seriously - have you checked the level? Perhaps there is too much oil in the crankcase. Secondly, does this just push in, or does it actually screw into the reservoir? If it only pushes in, check the rubber gromet - it might need replacing.