Intake Cam to vent cap problem 1959 G12 HELP!

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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Intake Cam to vent cap problem 1959 G12 HELP!

Postby Sibs6 » Wed Oct 02, 2019 1:14 pm

I purchased new cams for my engine a while back. When fitting the round disc(with the hole through it) for the vent into chamber on the primary side, and aligning with the female end of the intake cam , The disc protrudes out too far and the vented cap hits the disc.
The vent cap binds on the disc with a 1/8 gap between cap and engine case.
The disc does not recess into the chamber far enough. Female end of cam has a 10.mm recess and the male side of the disc is 4.5 mm
The Disc is my original from the motor but I fear the cams are wrong. It looks like the female end of the cam is deeper then the male end of the disc thus preventing the proper fit.

Please help, Have I got the wrong cams????

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Re: Intake Cam to vent cap problem 1959 G12 HELP!

Postby JEAN-NOEL » Thu Oct 03, 2019 4:43 am

Hello,
assuming you have a G12 original engine, there in not vent disc on the inlet camshaft ! Only the earliest 500 twin had them.
The vent valve is in the primary chaincase on the crankshaft.
Kind regards.

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Re: Intake Cam to vent cap problem 1959 G12 HELP!

Postby Sibs6 » Thu Oct 03, 2019 11:57 am

Can I post a couple pics here? or at lease send them to you Jean? I don't see where I can add images.

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Re: Intake Cam to vent cap problem 1959 G12 HELP!

Postby ajscomboman » Thu Oct 03, 2019 4:00 pm

You can only post pictures if you are a fully paid up club member. To be honest if you're planning on a rebuild it maybe worth the while to join, that way you'll have unlimited access to the forum and all the help you require. As guest you only have 90 days and limited access.

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Re: Intake Cam to vent cap problem 1959 G12 HELP!

Postby JEAN-NOEL » Fri Oct 04, 2019 8:32 am

Hello Al,
I can confirm that the rotating "disc" was discarted since 1951. Crankcase pressure release valve for 1952 - on was a diaphram valve fitted on the drive side of the crankshaft. What is the number stamped on your crankcase ?
A agree with Rob : the best way to get help in your restoration project is to become a club member.
Kind regards.

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Re: Intake Cam to vent cap problem 1959 G12 HELP!

Postby Sibs6 » Fri Dec 13, 2019 1:34 pm

Thanks all, problem solved with your help.
Meant to reply a while back but just got busy.

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