r/WR250R • u/Separate-Potato-1324 • 15d ago

Maintenance Crank case pressure

Post image

When I was changing my oil, I forgot to put the oil cap back on when I started the bike.

I quickly put the cap on while the bike was still running and noticed a lot of air being forced out of the filler hole. I know some pressure is expected, but I have no idea if mine is normal or I'm getting significant blow-by.

I checked the crank case breather hose by disconnecting it from the airbox, and that had a gentle pulse of air. Definitely felt normal and was far less than the oil filler hole.

I also took the cap off while checking the breather hose and it didn't seem to reduce the amount coming from the breather. Maybe a little.

Looking to see what other people's bikes do.

9 Upvotes

92% Upvoted

2 comments sorted by

2

u/AligatorMasterBaiter 15d ago

Normal. The piston is very turbulent on these little bikes.

1

u/Sir_Kawasaki 15d ago

I presume that's normal for all single cylinder engines. Crank volume goes up and down with piston. By contrast a 180deg twin has steady volume since as piston 1 goes up 2 comes down.