Crankcase vent

[Wilson]

This is a newby race question, but why do I need a bigger crankcase vent than comes on a stock ‘85 Slabbie engine?  I have seen many venting systems on race prepped bikes but have never understood the reason why when a venting systems already exists on the bike.  If it is a good idea how should I run the vent hose?

[Guest YoshiJohnny]

If you don't have one they tend to pressurise the crankcases when they are revving flat out for long periods, that results in power loss as the pistons are fighting against the pressure (not huge amounts but well...y'know...racing and that....) I just ran them from the oil filler to a catch bottle easy peasy... Hel do the fittings and the adaptor for the filler cap

[Wilson]

I’m still a little confused.  What then is the function of the vent and hose running from the top of the engine to the air box?

[MeanBean49]

41 minutes ago, Wilson said:

I’m still a little confused.  What then is the function of the vent and hose running from the top of the engine to the air box?

It is a vent, it goes to the airbox so oil mist goes through the engine and not all over.

The vent is too small though for constant high rpm. A bigger vent from oil filler into the airbox would work better.

When you ditch the airbox you need somewhere for the oil to go, so a catch bottle is the best bet

[Wilson]

Thanks for clearing that up for me.

[Dezza]

What if fitting a breather to the oil filler is impossible? I ask as my non-Suzuki frame means the frame spar is so close to the oil filler an aftermarket breather will not fit. Can one be fitted elsewhere?

[KATANAMANGLER]

I will be putting an alternator blanking plate on this year as I will be running total loss. My intention is to fit a vent hose on there instead of from the clutch cover.

[dupersunc]

I weld a tube and an10 fitting to the clutch cover.

[R1guy]

I just got this turned up. Same diameter as the breather on top of the cam cover.