B31 Timing Case Breather

[Grumps]

Hi
I have just taken off the timing case cover of my B31 to replace the gasket.

At the bottom there is a breather that vents via a pipe to the atmosphere. Inside the cover the breather is a short metal pipe crimped over at it's internal end. If I blow down the fitting from the outside it seems to be blocked - which I would expect as it's crimped over.

Can anyone please explain the function of this breather and what I should check on it before I refit the cover?

Thanks

[JulianS]

The valve should only allow air from the inside out, you should not be able to blow throught it from the outside. Check the crimped tube and you will find a hole drilled in the side which allows the air to escape. There is a disc inside the valve.

[Spaceman]

As said, there is a hole near the crimped end, obviously on the side you can't see in the picture, and the air pressure created by the falling piston pushes the disc valve open to allow air to escape to the atmosphere. The crimped tube is used to keep the exit hole clear of the oil level inside the case.

[Grumps]

Cheers lads. All ok then. Thanks.
Case back on. Seems oil tight 👍👍

[Grumps]

Should I feel pulses of air coming out of the open end of the breather pipe where it ends behind the primary case?

[Spaceman]

If the breather is working properly then that's exactly what I would expect. If there's not pulses of air coming out it probably means the disc valve is not being opened or the inlet or outlet tube is blocked.

[Grumps]

Thanks. I'll check.

I also ride several modern bikes. Press a button and go 😂👍 Nostalgia is hard work 😂

[Spaceman]

Modern bikes are fine but, when the ECU refuses to fire up the starter, they can be a nightmare to debug. You don't need a PC and an OBD2 adaptor to sort out classic bikes

[EDDIE SIMPSON]

yes nostalga is hard work. 2 minutes trying to start my old gsx1100 and the battery was flat and no kickstart. if it wasnt in top tune it was a hard starter and the batteries hated cold weather. 3 or 4 kicks on my b31 at most. any weather. i also see less of Arther Pullout on my old thumper.

[Grumps]

I ran the engine but there was no discernable air movement at the end of the breather pipe. (The one at about 7oClock on the timing case. It has a copper crimped pipe inside the case.Talking to C&D Autos these valves are not available now but they are able to be dismantled. I might do that next to see if it's blocked.

But, what if it is not working properly? What is the effect on the engine? Does it matter?

Cheers

[Spaceman]

I am sure you will find the breather is slightly blocked or the disc valve is stuck in the closed position and, after taking it apart, it hopefully be easy to sort the problem.

In terms of whether the breather is really necessary, this is a relatively small engine and it is probably marginal in its effect. In the worst case, you could probably remove the disk value and leave the breather open to the atmosphere.

[Grumps]

Cheers Spaceman.

[Rog1]

I ran the engine but there was no discernable air movement at the end of the breather pipe. (The one at about 7oClock on the timing case. It has a copper crimped pipe inside the case.Talking to C&D Autos these valves are not available now but they are able to be dismantled. I might do that next to see if it's blocked.

But, what if it is not working properly? What is the effect on the engine? Does it matter?

Cheers

The effect of a non functioning breather on my engine (though it's the 500cc version) was to make engine oil pour out of the primary side main bearing like a waterfall. Most of it went on the road, except for what went into the primary case. It raised the oil level (!) enough that I had to strip the clutch to get all the oil off. I dismantled the valve, cleaned it all up and rebuilt it, and made sure the disc made a clicking sound every time I turned the valve upside down, before replacing it. Before you ask, no; the bike doesn't wet sump.

What I don't think has been mentioned is that there is a hole in the crimped pipe which should face towards the outer casing and very slightly back.

[Grumps]

Thanks Rog1. Something else to check !!!

[Rog1]

Thanks Rog1. Something else to check !!!

I forgot to say: to get the hole in the crimped pipe to point where you want there's a usually a certain amount of faffing around with different thicknesses of cardboard gasket between the valve and the timing case. It can be done with the case on the bike if you mark the valve body to show where the 'ole is.

I've just realised that not being able to blow through the valve from the outside pipe means the valve is either working (it's a valve!), or blocked/stuck shut.