Matchless/AJS pistons interchange?

Knut1976 · Post by **Knut1976** » Wed Aug 17, 2011 9:26 am

Hello,
Sorry this may be a dumb question for you guys but I need some help as I'm not familiar with British bikes (I work with old jap two-strokes only...).

Do Matchless and AJS share the same engines and are pistons interchangable? I'm helping a friend to find pistons for a 1963 Matchless G12 CSR he's working on. As I understand it, the G12 CSR Monarch and AJS 31 CSR Hurricane is basically the same bike. Redlizard Classic Motorcycles lists pistons for the 31 CSR but not for the G12 CSR. So can I buy these pistons for the Matchless?
Here's the link to the pistons: http://www.classic-motorcycles.co.uk/cg ... b_pid=5973

I've found listings for the correct Matchless pistons elsewhere but with small dealers on the other side of the planet who doesn't accept online payment (paypal) so it makes it a bit of a hassle. It would be much easier for me to just order from this website and pay online, and shipping to my country (Norway) would be cheaper.

Is there anything I have to take into consideration when bying pistons, or is it straight forward as long as it is listed for the correct bike? The current pistons are marked 040 (+1mm oversize), the cylinders have some scoring and need to be bored so I have to go up one more size to 060 (+1.5mm).

Thanks for any help and advice.

Knut.

Rob Harknett · Post by **Rob Harknett** » Wed Aug 17, 2011 10:49 am

Knut, Check out the clubs spares dept. Jampot Spares. You will find it on this website. We have pistons, all sizes. You will have no problems buying from the club. Join the club plus take the club spares discount option. You will almost get back what the membership costs buying the pistons at the club discount. You will also discover we will have almost any part you may need. Our helpful staff at the club HQ will soon have the correct pistons in the post to you and no problems making payments. We have about £350,000 worth of parts in stcock.

Rob Harknett · Post by **Rob Harknett** » Wed Aug 17, 2011 10:57 am

You will see from the club spares some years pistons differ also G12 differ from G12 CSR, you can check parts lists for correct part numbers here:
www.archives.jampot.dk

Don Madden · Post by **Don Madden** » Wed Aug 17, 2011 5:18 pm

Ignore the model names as "Monark/Hurricane" as they only applied to late models. Use G12CSR/31CSR & always specify the year as changes were made periodically. Pre-1960 top end parts do not interchange with later. Cheers, Don.

Knut1976 · Post by **Knut1976** » Wed Aug 17, 2011 5:30 pm

Thanks for the replies.
So I understand correct that the M G12CSR and AJS 31CSR from the same year (in this case 1963) share the same pistons?

I found the Jampot spares dept, has to go through it later when I have some more time.

Thanks again.

Rob Harknett · Post by **Rob Harknett** » Wed Aug 17, 2011 6:52 pm

All your questions would be answered when you check Jampot spares stock of pistons for heavyweight twins as I advised earlier.

wilko · Post by **wilko** » Wed Aug 17, 2011 11:15 pm

Those JP ones don't have the raised lump as per standard 8.5 compression?Anyway i would suggest 7.5 for sweeter runnng, as these big twins do vibrate.