G9 Cylinder Head design Changes

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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craigcc
Posts: 21
Joined: Wed Oct 03, 2012 10:15 am
Location: CORNWALL UK

G9 Cylinder Head design Changes

Post by craigcc »

Hi all,

I'm trying to source a set of heads for my '53 G9. (in order to test feedback from various folk on my cylinder oiling problem - different thread)

But I've noticed that the cylinder stud placings change, with heads seemingly not interchangeable between various year ranges. The placings are only slightly different and I've already been caught out a couple of times purchasing heads on spec and finding they simply don't fit. It doesn't help that part numbers are often absent from heads. It would seem that heads for my bike are not that easily found.

Looking through the excellent primer on year by year changes for twins, it doesn't seem to cover this issue.

Can anyone advise on this? On which years did the various change overs for stud placings happen?

Thanks.

Craig.
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robcurrie
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Re: G9 Cylinder Head design Changes

Post by robcurrie »

Craig, read the technical article on the club site about interchangability of parts on twins an note the last comment on the article by dave650ss.

Rob C
craigcc
Posts: 21
Joined: Wed Oct 03, 2012 10:15 am
Location: CORNWALL UK

Re: G9 Cylinder Head design Changes

Post by craigcc »

Excellent, thanks - answers my question. Coincidently, I spent the last hour listing cylinder barrel part numbers from the various years and they do change after 1955. All previous had the same part number.

Just annoying that so many heads have no part number stamps. Makes acquiring a set difficult, though I note that pre 55 heads don't have the channel cut into the valve rockers. The USA seems to be a good source of supply for heads - at seriously inflated prices.

Craig.
alanengineer
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Re: G9 Cylinder Head design Changes

Post by alanengineer »

i didnt think twin heads were hard to get. Havnt looked for years, just assumed. Have to lock my set up in the safe, i think.
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