Is it normal for my bike to...............

[jordanearl]

have a lot of air pressure inside the engine after i have ridden for 15 to 20 minutes?  i went to check the oil after a ride to work today, and there was a lot of pressure relaeased when i opened the oil cap.  Is this normal?also, the oil level is at full and looks brand new.(changed oil about 500 miles ago)

[mjm]

have a lot of air pressure inside the engine after i have ridden for 15 to 20 minutes?  i went to check the oil after a ride to work today, and there was a lot of pressure relaeased when i opened the oil cap.  Is this normal?also, the oil level is at full and looks brand new.(changed oil about 500 miles ago)

No.  There should not be any pressure in the crankcase

The crankcase is supposed to be vented through a hose from the top of the valve cover to the airbox in stock configuration.  If individual or "lunchbox" type air filter has been installed then it is either vented to air or through a filter on the end of the hose.

[jordanearl]

so what should be my course of action?  What are the negative affects of this happening?

[Jake D]

Try taking the dip stick out when the engine is warmed up, idling, and on the center stand.  Note any change in the idle and report it here.

What year is your bike?

[mjm]

so what should be my course of action?  What are the negative affects of this happening?

Check that the vent hose is not kinked or blocked.   A SMALL amount of air "puffing" in and out of this hose is normal as the crankcase volume changes with the pistons moving up and down - a large amount indicates some problems - particularly bad rings.  If ther engine is running you may also get a bit of "puffing" from the oil fill opening if you unscrew the dipstick.

Do a compression and leak-down test to see if there is excessive blow-by.

[scratch]

Be careful not to get the dipstick caught in any gears when you unscrew it while the engine is running! Also, be prepared to be sprayed by oil being flung off by said gears. Unscrew the dipstick and look in there before starting the bike.

Another thing would be to squirt some oil in the sparkplug holes to see if that increases compression after you have run the bike so you can hear the difference.

[jordanearl]

i had just had the carbs rebuilt by the local bike shop.  So I went back there and showed him.  Easy fix, he had forget to place the hose back on airbox, all is good again.  Thanks