Oil Cap

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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Oil Cap

Postby Rosy » Sun Oct 13, 2019 3:33 pm

I have a new oil cap from the club spares for my 56 G9, screw on type, but it doesn't screw in it goes on about half thread then stops. Compared to the old one which has a slight taper from the cap to the end of the thread, the new one has a parallel thread, is this how it should be? if not should I try and file the thread with a thread file. Or may be send it back for another one. I need a new one because the old one has a 3mm hole drilled in the cap.

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Re: Oil Cap

Postby alanengineer » Sun Oct 13, 2019 7:15 pm

Maybe, you have an inclusion in the thread of the oil tank, run a tap down that to check

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Re: Oil Cap

Postby clive » Sun Oct 13, 2019 9:23 pm

I would imagine a thread would normally be parallel and the tapered one would be due to wear. I find that i have to be very careful when fitting my screw in cap that it is not wrongly threaded. If it is it only turns on half a turn before going tight. Having another try can start it properly.
clive
if it ain't broke don't fix

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Re: Oil Cap

Postby Rosy » Mon Oct 14, 2019 7:18 am

I thought of a tap, but a tap that large! and cost, I spent half an hour trying all ways to screw the cap in with no joy, it doesn't even feel like it will force in which is I suppose a good thing. I will at some time be taking the tank off I could then find an engineering shop that might run a tap through it. Any idea of the size of the thread?

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Re: Oil Cap

Postby Rosy » Thu Oct 31, 2019 6:57 pm

alanengineer wrote:Maybe, you have an inclusion in the thread of the oil tank, run a tap down that to check

Yes you are right an inclusion, the first few threads are damaged. but what size tap would I need? and where would I get one that big? or if any one has one could I please borrow it?

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Re: Oil Cap

Postby Group Leader » Thu Oct 31, 2019 9:51 pm

Maybe use a thread file in preference to a tap if you can find the appropriate size/thread form?

https://www.cromwell.co.uk/shop/cutting-tools/thread-restoring-files/thread-restoring-files/f/61

Alan
1953 AJS 16MS, 1939 BSA 250 and a 1/3 scale Sopwith Triplane but that's another story ..... :lol:

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Re: Oil Cap

Postby Rosy » Tue Nov 05, 2019 7:15 pm

Oil cap now screws in a treat, after recutting the threads with my adapted files that worked so much better than I thought they would.
I just need to know what holds the gauze oil filter in place? mine was half way down the rubber oil pipe, I'm ordering a new one as it's bit battered, and some half inch rubber pipe pipe.

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