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Author Topic: Crankcase Pressure  (Read 712 times)


  • Bulleteer
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  • Posts: 117
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Crankcase Pressure
« on: August 16, 2010, 09:43:44 am »
I did an oil change yesterday and forgot to refit the oil filler cap before starting the bike. It ran ok but what was surprising was the amount of crankcase pressure being vented from the oil filler hole, it was quite difficult to refit the cap with the engine running.

I traced the ‘proper’ breather from the R/H crankcase just behind the oil filler cap back to the airbox expecting there to be a similar level of venting (oil filer cap on and engine running) but it was hardly noticeable.

Strange that the crankcase breather doesn’t release as much pressure as the oil filler hole. Is this normal? Nothing seems wrong with the engine.


  • Bob's Your Uncle
  • Grease Monkey
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  • 2010 Black Bullet C5
Re: Crankcase Pressure
« Reply #1 on: August 16, 2010, 10:54:37 am »
Mine pushes out quite a bit of air in the airbox. I think what you're sensing there is just physics - a larger opening will have less restriction and push more air out.