Compression ratio of JP0633 + 0.020 Pistons

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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CAB
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Joined: Thu Jul 09, 2009 9:10 pm
Location: CORNWALL UK

Compression ratio of JP0633 + 0.020 Pistons

Post by CAB »

Hello
I have just started stripping down my 1961 G12 CSR to try and cure some oil leaks. The bike came with receipts for work that had been done in the past but there and two list pistons with different compression ratios. With the heads off I can see the part numbers on the pistons and these are JP0633 + 0.020 HJ. I'm hoping that these are the 8.5:1 type. Can anyone confirm this?
Thanks
CAB
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