Which is the best type of crankcase breather for a Trials Cub, some people leave the original with the small hole inside the r/h engine case.

Another method blocks this off and then a pipe is fitted from the screw in bung on top of the crankcases, I am told that one can also be fitted on to the head but I have yet to see this type.

So which method works the best.

Its the crankcase that needs to breath, the last two methods you mention both work fine, a breather tube stub can easily be fitted to the bung cap (1 inch long X 3/16 I/D x 1/4 O/D tube - alloy/brass) on top of the crankcae, you then fit a 1/4 I/D plastic tube long enough to tuck under tank, the second option is to fit a similar size breather tube to the either rocker cover, the plastic tube is then fitted and the much shorter tube again tucked under the tank - both methods work fine, I favour the first option being closer to the crankcase.

Hope this helps Brian H

certainly the breather using the cap in the top of the crankcase should have the most benifit and I followed this route using fuel type piping, having looked at a number of trials bikes since this method has been confirmed as the most popular, however pipes of much bigger diameter appear to be the norm with the max i have seen been 15mm ID, what differnce do they make unsure.. but making them up only took an afternoon and cost pennies,, music to any trials fan

Edited March 15, 200719 yr by totalshell

My initial choice of breather was the one on the top of the crankcases but I am concerned that the pumping effect from the underside of the piston might send oil up the pipe and out to atmosphere a sort of total loss system if you follow me, Is there any likelyhood of this occuring.

never had a drop out of my breather on the crankcase. although mine is an open pipe as described above. I am going to swap to the type of breather pipe found on royal enfields which have the open end 'nipped' up so that nothing can get 'sucked 'in

Thank you all for your ideas it sounds as though the crankcase breather is definitely the way to go.

Cheap way to the nipped up breather.

Cut a length from an old bicycle tube and fit it over the end of the open pipe.

The tube is naturally flat.

certainly the breather using the cap in the top of the crankcase should have the most benifit and I followed this route using fuel type piping, having looked at a number of trials bikes since this method has been confirmed as the most popular, however pipes of much bigger diameter appear to be the norm with the max i have seen been 15mm ID, what differnce do they make unsure.. but making them up only took an afternoon and cost pennies,, music to any trials fan

Which bung on the top of the crankcase are you talking

Vinnied

the larger diameter of the two (the smaller being the gearbox filler) i think this is where the distributer might be on some models

1,2,or3 totalshell

Vinnied

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3

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3

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was going ( and will still try to post a pic of mine)

best wishes

Did not mean to get you that mad cheers

See you at pre65

Vinnie

Edited March 22, 200719 yr by Vinnied

4 yr old daughter thought it was funny to put all the 3's cant find a photo close up but have this of John Maxfields bike to demonstarte the size of pipe some people go up to,

http://picasaweb.google.com/totalshell/Edi...762829491420802

Edited March 22, 200719 yr by totalshell