Blowing air

[Joshua Brew]

Hi guys. Just a quick one! Is it normal for my bike (1100evo) to blow a little bit of air throufh tbe filler cap when the bike running. It doesnt use any oil and it runs just fine. Just noticed when i was messing about in the garage. Im sure its dine just welcome you opinions
Cheers

[350TSS]

Presumably with the cap removed and engine running then the air in the crankcase beneath the pistons has to go somewhere - usually out of the engine breather but like electricity it will take shortest path if the cap is off.
Interesting aside a single cylinder configuration can never produce as much power as an inline 4 because of pumping losses.
In a 4 the crankcase pressure stays pretty much the same, because as one piston descends another rises by the same distance so the pressure beneath the piston is pretty much constant. A single has to displace its swept volume of air on the power and exhaust strokes.

[Joshua Brew]

Presumably with the cap removed and engine running then the air in the crankcase beneath the pistons has to go somewhere - usually out of the engine breather but like electricity it will take shortest path if the cap is off.
Interesting aside a single cylinder configuration can never produce as much power as an inline 4 because of pumping losses.
In a 4 the crankcase pressure stays pretty much the same, because as one piston descends another rises by the same distance so the pressure beneath the piston is pretty much constant. A single has to displace its swept volume of air on the power and exhaust strokes.

Hi, i like the way you think. Nice practical approach. Thanks for the reply. I will be able to sleep at night.

[TimDW]

Hi guys. Just a quick one! Is it normal for my bike (1100evo) to blow a little bit of air throufh tbe filler cap when the bike running. It doesn't use any oil and it runs just fine. Just noticed when i was messing about in the garage. I'm sure its dine just welcome you opinions
Cheers

This is normal. It is the crankcase pressure. Normally it goes through your blow-by (engine breather) to the airbox. But as 350TSS said, it takes the easist way.