Triumph 500 twin

[Admiral_dk]

I must have misread something earlier - as I thought you had done that 

But it do explain why I didn't see them in the last picture ....

Per

[John Roberts]

 Jasonb has brought up the subject of crankcase breather pipe on another thread, I had not given this any thought for my Triumph twin. which is 50cc.
Could I get away with a 6 mm bore  breather pipe?

[Roger B]

I would think so. my 12 cc twin has a 2mm breather hole. If I remember correctly it is a parallel twin so it will be displacing the full volume of air. Hopefully you won't have much piston blow by to deal with.

[John Roberts]

Thanks Roger.

[Admiral_dk]

If you do as Jason suggested and put in an one-way-valve,  so you end up with a negative pressure inside the Crankcase - then all is good, as you wont get any leakage + you reduce the pumping losses.

My (old) full size engines have approx. Ø12mm. hole for the breather - for 550-1100cc. - the nevest I believe is Ø16mm. for 650cc.

Per

[John Roberts]

I think Per I have it about right, scaling up Rogers engine breather and down a full size one. I will be be adding a one way valve as suggested.
Thanks, good idea.