AJS & Matchless Owners Club

Hi!
I'm fully restoring a -54 Matchless G3L, and I've noticed something interesting about the crank case vent. The steel membrane on my machine was looking a bit sad (bent/convex) so I ordered a new one from the club store among some other things. Anyway, the new membrane is about twice as thick as the old one, and will not be able to move freely if assembled(!)

The old membrane was about 0.2mm, and the new one was 0.4mm. Now which is it supposed to be? Anyone noticed this before? How much should this membrane be able to move?

(Sorry about the metrics but I'm swedish...)

There is the old mantra, if it ain't broke don't fix it.

Was the breather working? They always drip a bit.

Mine's the same that was in it 40 years ago when I got it; still working. But it is flat. Never measured it, sorry.

Johnny B

Mmm, yes but I guess I'm a bit of a perfectionist... Perhaps a bad choice of motorcycle Good thing that I've got a Suzuki too, which is a fantastically trouble free machine but somewhat boring...

It was probably dripping a bit. The bike came with a nice oil collecting oven pan when I got it I more or less tore the bike apart down to the lucas horn right after buying it... Most original parts were attached, but the bike really needed a restoration.

Hej Arcturus,

I've just been and measured one in my shed. It was exactly 10 thousandths of an inch which is 0.254 mm according to the internet.

John

Thanks! This confirms my hunch that the old one is of correct thickness. The new membrane is to thick and won't be able to move if assembled. Watch out for this if replacing the membrane!

I am not sure that the thickness is that critical. I have an early Triumph twin which has a brass diaphragm in the breather valve and the brass is much thicker than 0.010". I dont have the measurement at the moment (I am at work) but I am thinking 0.70mm to 0.90mm thick, say 0.30" to 0.035".

If replacement membranes are too thick then surely there would be loads of comments on this site from those people who have them?

John

On my bike it won't move if I assemble the thicker membrane. Perhaps there isn't enought clearance to begin with..? Perhaps that's why the old membrane looked bent/convex..? Ehhh, I need to look into this again.