SR1 Magneto Position/Clearance

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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SR1 Magneto Position/Clearance

Postby George Kaplan » Sat Apr 13, 2019 1:45 pm

Johnny B stated over in my build thread that he had to trim some of the fins on his 500 cylinder to get his SR1 to fit. I have a similar issue. My chain rubs on the casing so the mag needs to move backwards but is prevented because it is touching the fins on my 500cc cylinder. Before I reach for the grinder I was wondering if that is what everyone does? (The N1 mag is shorter so doesn't have this problem)

Whilst I don't have any issues with trimming a couple of fins I thought I would canvas opinion?

One alternative option would be to fit two smaller sprockets and a shorter chain but trimming the fins will be easier and cheaper.

What do you think?

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Re: SR1 Magneto Position/Clearance

Postby Mick D » Sat Apr 13, 2019 2:05 pm

Hi

I responded to this question in the other thread and asked if the components were incompatible - is the N1 mag the correct one by design?

Two threads for the same question.

Regards Mick

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Re: SR1 Magneto Position/Clearance

Postby George Kaplan » Sat Apr 13, 2019 3:15 pm

Thanks Mick for the reply,


Mick D wrote:Two threads for the same question.


I posted on here because its a public forum so people will see it if they haven't logged in.

I posted on my build thread so I could quote Johnny B but because admin have made it private it can only be seen when logged in.

Dont blame me for two threads for the same question, blame admin.

John

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Re: SR1 Magneto Position/Clearance

Postby Rob Harknett » Sat Apr 13, 2019 4:43 pm

The mag looks very close to the fins, So could be wrong mag or barrel. Just a long shot, has the chain the correct number of links? A shorter chain may lower the mag to clear fin and casing. Although it looks too tight to me.

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Re: SR1 Magneto Position/Clearance

Postby clive » Sat Apr 13, 2019 5:54 pm

So the correct 500 barrel for the SR1 mag had the bottom four or five fins cut away to allow adjustment of the chain. The 350 did not need it. So if you want to keep the SR1 be reassured the fins should be cut. The postwar Matchless 500s were similarly cut back to fit the N1 mag behind the barrel. Obviously with the SR1 the cut is at the front.
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if it ain't broke don't fix

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Re: SR1 Magneto Position/Clearance

Postby George Kaplan » Sat Apr 13, 2019 6:54 pm

Thanks everyone for the replies.

The mag chain is 46 links which I believe is the right length.

I will make some adjustments to the front of the cylinder bit at a time until I have enough clearance.

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Re: SR1 Magneto Position/Clearance

Postby alanengineer » Sat Apr 13, 2019 6:58 pm

Thats a shame to butcher a good barrel. if we were closer i would offer to swap for the right one

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Re: SR1 Magneto Position/Clearance

Postby George Kaplan » Sat Apr 13, 2019 7:34 pm

Hi Alan, I have pm'd you.

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Re: SR1 Magneto Position/Clearance

Postby Andy51 » Sat Apr 13, 2019 8:41 pm

I had the same problem years ago, after buying a '54 G80 fitted with the wrong barrel and N1 magneto. I got the correct SR1 magneto and wrestled for hours trying to get it to fit until I realised the barrel was wrong. I had the fins machined and everything fitted perfectly. You will not get the SR1 to fit unless you have the right barrel, or the wrong type machined. Swapping barrels is the ideal way forward, but then you may run into problems with piston/bore compatibility. Your call! Andy

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Re: SR1 Magneto Position/Clearance

Postby Mick D » Sun Apr 14, 2019 8:41 am

alanengineer wrote:Thats a shame to butcher a good barrel


Hi

I agree - I'd be looking for a compatible mag.

Regards Mick

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