AJS /Matchless 650 standard twin fitting CSR 8.5 pistons

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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tarrya
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Joined: Sun Jan 01, 1995 12:00 am
Location: EAST SUSSEX UK

AJS /Matchless 650 standard twin fitting CSR 8.5 pistons

Post by tarrya »

Has anyone fitted the higher compression pistons to the standard 650? Will the bottom end cope/ are the csr/ standard bottom end the same. Thanks in anticipation for any info.
JEAN-NOEL
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Re: AJS /Matchless 650 standard twin fitting CSR 8.5 pistons

Post by JEAN-NOEL »

No problem Steve. You have only to set the ignition at 34° instead of 39°according the owner's manual. You can swap the main jet 390 with a 450 one. But I don't think you want to ride your bike full throttle !
tarrya
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Joined: Sun Jan 01, 1995 12:00 am
Location: EAST SUSSEX UK

Re: AJS /Matchless 650 standard twin fitting CSR 8.5 pistons

Post by tarrya »

Thanks Jean-Noel for your reply and info, cheers Steve.
mjf65
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Re: AJS /Matchless 650 standard twin fitting CSR 8.5 pistons

Post by mjf65 »

I thought the ignition timing is 35° (11/32) for all 650 models?
I was also told that 8.5 pistons are no longer available? I've no idea what's in mine but I intend to leave them well alone as they seem to be working well with minimum oil consumption and healthy compression.
JEAN-NOEL
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Re: AJS /Matchless 650 standard twin fitting CSR 8.5 pistons

Post by JEAN-NOEL »

Sorry Steve ! Michael is right : the ignition timing is definitively 35° - 11/32 for all 650 (except if hi comp pistons, 10.25 ratio are fitted : 29°). 39° - 3/8° is only suitable for 500 & 600 twin. Checked in 62, 63, 64 owner's manuals, and workshop manual 57/64. And yes pistons 8.5 CR are unavailable from AMOC PARTS in Std, +0.20, +0.40, only +0.60.
Cheers. J.N.
Groily
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Re: AJS /Matchless 650 standard twin fitting CSR 8.5 pistons

Post by Groily »

Might just be worth checking Feked and also British Only Austria for 8.5s in the other + sizes. They seem to list them (JPs) and Feked's online shop says they have 'em (if you start to pretend to order some).
I've been running my Mod 31 with 8.5 +20 JPs - supplied in fact by T&L Engineering - for a good few years without problems on a new Club crank and some Thunder rods.
But STD 72mm, not shown anywhere I can see.
tarrya
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Posts: 4
Joined: Sun Jan 01, 1995 12:00 am
Location: EAST SUSSEX UK

Re: AJS /Matchless 650 standard twin fitting CSR 8.5 pistons

Post by tarrya »

Thanks for your help, much appreciated .
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