61 M20 crankshaft non return / breather valve

Information relating to the Matchless G9 or AJS Model 20 500cc twin
Member
Posts: 8
Joined: Sat Aug 19, 2017 9:14 pm
Location: SOMERSET UK

61 M20 crankshaft non return / breather valve

Postby bsazb34 » Sun Aug 20, 2017 10:25 am

Hi there,
I have just completed a full restoration of my 1961 Model 20 but on first running the primary just filled up with oil even though I was getting oil from the tank return. Having stripped the primary case again I looked at the crankshaft end diaphragm valve and was surprised to see that the diaphragm was free to move about within its body. I don't know if this is how it is supposed to be but it looks to me that this will allow any oil pumped into the crankshaft to pass through and flood the chain case.
Can anybody advise me on this.

bsazb34

Member
User avatar
Posts: 1774
Joined: Mon Jan 01, 1990 12:00 am
Location: LANCASHIRE UK

Re: 61 M20 crankshaft non return / breather valve

Postby dave16mct » Sun Aug 20, 2017 10:50 am

The usual cause of this is that the owner tops up the oiltank before the engine has been warmed up. The oil that has dropped into the crankcase hasn't been pumped back into the tank. It floods the chaincase through the crankcase breather. Worse if left on the side stand.
Drain out the chaincase untill it is just below the bottom edge of the chain. Drain the crankcase and try again. Also sounds like you need a new breather valve.
Dave.

Member
Posts: 8
Joined: Sat Aug 19, 2017 9:14 pm
Location: SOMERSET UK

Re: 61 M20 crankshaft non return / breather valve

Postby bsazb34 » Sun Aug 20, 2017 11:10 am

Thanks for that I'll get a new breather and try again

Member
Posts: 8
Joined: Sat Aug 19, 2017 9:14 pm
Location: SOMERSET UK

Re: 61 M20 crankshaft non return / breather valve

Postby bsazb34 » Thu Aug 24, 2017 10:05 am

Hi again,
So I got another breather valve from the club but am rather confused over how it is supposed to work. Fresh out of the box I placed it 'nose down' on the bench and filled the back of the unit with cold fairly viscous oil and watched as it just started to ooze through valve. My problem is getting it through my head how this is supposed to stop pressurised low viscosity, hot oil, from passing straight through and once again flooding the chain case and eventually the floor, what makes it seal?

Member
Posts: 574
Joined: Thu Feb 27, 2014 9:27 am
Location: Kent, England

Re: 61 M20 crankshaft non return / breather valve

Postby JimFitz » Thu Aug 24, 2017 1:28 pm

The valve is designed to stop a pressurised oil mist so clean all the oil off and then try to blow through it from the crankshaft side - it should close. You should be able to suck air back through it.
After I cleaned mine up I ran it with the primary cover off and I could feel puffs of air on the back of my hand as it was opening and closing.

Jim
Too old to Rock and Roll but too young to die.

1952 G80 rigid, 1960 G12 DL / Watsonian Monza, 1954 G80S.

Member
Posts: 8
Joined: Sat Aug 19, 2017 9:14 pm
Location: SOMERSET UK

Re: 61 M20 crankshaft non return / breather valve

Postby bsazb34 » Thu Aug 24, 2017 1:36 pm

Thanks for That Jim, when I got the new one today I tried blowing through it as you described but it seemed to put up little resistance to the air flow and definitely didn't close I haven't tried fitting it yet and probably won't get a chance before next weekend so just have too see what happens then.

Chris

Member
Posts: 8
Joined: Sat Aug 19, 2017 9:14 pm
Location: SOMERSET UK

Re: 61 M20 crankshaft non return / breather valve

Postby bsazb34 » Thu Aug 24, 2017 1:37 pm

Sorry Jim did you mean blow through from the crankshaft or crankcase side?

Member
Posts: 574
Joined: Thu Feb 27, 2014 9:27 am
Location: Kent, England

Re: 61 M20 crankshaft non return / breather valve

Postby JimFitz » Thu Aug 24, 2017 1:47 pm

From the crankshaft side (I think). It was a while ago when I did mine - well more than two weeks :D .

It should only pass air in one direction in any event.

Jim

The more I think about it I think it should pass air from the crankshaft side and not from the chaincase side.
Too old to Rock and Roll but too young to die.

1952 G80 rigid, 1960 G12 DL / Watsonian Monza, 1954 G80S.

Member
Posts: 8
Joined: Sat Aug 19, 2017 9:14 pm
Location: SOMERSET UK

Re: 61 M20 crankshaft non return / breather valve

Postby bsazb34 » Thu Aug 24, 2017 2:09 pm

Thanks again Jim I think I'll have to fit it and give it a go. This all stems from the end of a four year rebuild when last Saturday I took it for an MOT and it pumped a full tank of oil apparently through the valve and into the primary chain case and subsequently all over 2 1/2 mile of road in Bridgwater.

Chris

Member
Posts: 140
Joined: Wed Oct 12, 2005 9:45 pm
Location: MIDDLESEX UK

Re: 61 M20 crankshaft non return / breather valve

Postby John Jarrett » Thu Aug 24, 2017 5:52 pm

Are you sure you have your feed and return pumps the right way round on the oil pump plate. The return pump is the wider of the two and goes on the left side of the pump plate as you look at it from the timing side.

Next

Return to G9 / AJS Model 20

Who is online

Users browsing this forum: No registered users and 1 guest