AJS & Matchless Owners Club

I have been looking for a 8:1 high compression piston for my G2 project. I was sold one by Roy Bellet but I am unsure if it is the 8:1 CSR piston or the 10.5:1 scrambler engine piston.
To me it looks a little tall compared with the standard piston in the picture to give just an increase from 7.8:1 up to 8:1 for the CSR, looks more like a hike up to 10.5:1 for the scrambler, though it could possibly be a 1965 on CSR piston which was upped to 9.5:1.
Can anyone with certainty identify the piston on the right as to wheather it is an early CSR piston, a later CSR piston or a Scrambler piston? There are no identity numbers or letters on the piston.

Laurie

To positively identify can you post a picture of the crown of the piston?

It's a CS piston 10.5 - 1 without a shadow of a doubt. I know that because the other guy who wanted to buy it before you got to Roy's stand specialises in CS lightweights and required it for a project.

Thanks Rob, I suspected as much, shame I've parted with £30.00 for something I can't use.
I've posted a picture of the piston crowns so that John Jarret can also confirm what you have said, thanks John in anticipation.

I'll have to post a wanted Ad. to see if anyone has a CSR piston going begging.

I wonder why the club doesn't stock them, there seems to be quite a few Lightweight CSRs in the club.

Laurie

Being such a good chap and don't want to spoil my reputation 100 % refund just bring it back next Saturday.

Thanks Roy, will do, what a good chap you are.

Laurie

Thanks for the picture of the crown of the piston. Rob, it may be a CS piston but it is definitely not a 10.5:1 piston. I have attached a picture of the crown of a genuine BHB CS 10.5:1 piston which has a much higher crown. Kind regards,
John

dodger wrote:I'll have to post a wanted Ad. to see if anyone has a CSR piston going begging.

I wonder why the club doesn't stock them, there seems to be quite a few Lightweight CSRs in the club.

I don't know for certain why not but I suspect that one very good reason is that there were 4 different standard piston manufactured for 250 lightweights. The early CSR used the same as the G2/M14, the 1965/66 CSR had a different one and the CS had two in different years. Add to that the different oversize pistons that later owners require and you'd need a stock of at least 4 sizes for each one, so 16 pistons and rings to cover every requirement.

The spares department stock pistons for the basic G2/M14. I don't know whether these could be used in the CS or later CSR, with presumably a reduction in performance. My 64 CSR has the same barrel and head as the 65/66 CSR but uses the same piston as the G2 so I can get one if I need to. These days with a small old bike, 75mph is fast enough for me. I never was a daredevil thrill seeker.

Now I don't really know what I've got, John Jarre'ts picture of the piston crown certainly looks to be a taller example than mine as the flat band across the top is narrower than mine, perhaps it is a 9:1 later CSR item after all.

Anyone else got any ideas?

Thanks John for the input.

Laurie

Going through my scrap second hand pistons, the "match" by eye to the shape of the crown on your piston is 043646. That piston is from a 1965/66 CSR. From the promotional material the stated compression ratio in 1965 was 9.5:1.
Kind regards,
John