Engne breathers

Morning All

The 6mm bore breather pipe that terminates in a ring at the back of the gear box leaks a little oil, and since I don’t tend to rag the Cali about too much I was wondering why since I don’t appear to be loosing any oil

So, I might be out thinking myself her, but given that my bike is knocking on for 20 years old is there any need to clean out the breather system and if so how to do it??


Hi Tris, first job is to check the gearbox oil level, if more than expected comes out of the level plug there is a possibility that bevel box oil is transferring via the drive line, which means replacing a couple of seals. If all is well, level wise, then this is usually due to over-enthusiastic use. There is often the odd drip from this breather so the solution could be just to fit a longer pipe that goes up a bit more in a longer loop. Let us know how you get on.

If the bevel box is transferring oil into the gearbox then first thing is to burp it.
Get everything nice and warm, crack open the bevel box filler plug then screw it shut.
This creates a minor vacuum in the bevel box that can solve that problem.
Apparently, according to men who know, this shouldn’t work.
It often does.

“6mm bore breather pipe that terminates in a ring at the back of the gear box

This sounds more like engine breather actually, the hose terminates at rear of gearbox, but does not originate from gearbox.

EDIT: (excessive) oil loss from engine breather is a sore point with me at the moment!

EDIT: is yours a Tonti framed Cali?

I was trying to ask about the engine breathers not the gearbox. But maybe my description lead to the gear box breather :frowning:

Re gearbox
I had a problem with the gearbox output seal and the oil was going the other way into the bevel box. I think that’s sorted out now.
Burped the bevel box as a precaution anyway

Re Engine
I know everything goes up to the top frame tube but I’m a bit nonplussed as to exactly what does what and whether there could be a load of Cr*p in the frame stopping it doing whatever its supposed to do :blush:

Mike its a Tonti framed Cali

The engine breather tube from the engine block is a lot bigger than 6mm.

As I understand it the engine breathes via the rocker covers, the vapour goes into the top frame tube, and any oil which condenses drains back through the large diameter tube just in front of the bellhousing. The rest of the vapour is fed into the air cleaner box to be burnt in the engine.

Isn’t it a different frame that uses the top tube tho?

@ gtmdriver yes but he means the open-ended 6mm hose that ends in a ring at the back of the gearbox.

This would be the ‘overflow’ …

If I’m reading the parts list drawing properly there appears to be a one way spring loaded ball valve in there at the bottom.

Is this known to bung up/stick?


A lot depends on the state of your engine and your oil but the ball valve can indeed gum up and stick.

Aha - I think I’ll rave that out - if only for peace of mind!


It’s not spring-loaded it only works by gravity.

Never heard of one sticking and I think it would be very difficult to do, or something very wrong with your oil.

PS: (omission) what could do with checking is the general state of the hoses and clips.

Also blow air down the small bore metal drain tube to make sure it is clear.