'59/60 Cylinder heads

Information relating to the Matchless G12 or AJS Model 31 650cc twin
Member
User avatar
Posts: 398
Joined: Sun Mar 18, 2018 12:02 pm
Location: Bristol UK

'59/60 Cylinder heads

Postby Martin.S » Mon Oct 15, 2018 6:46 pm

Can anyone explain to me the difference in the pre and post 1960 cylinder heads? The spigot diameters are 0.060" bigger on the later heads but what of the shape of the combustion chambers and their roof heights?
I'm asking because the '59 pistons fit into the 350cc lightweight but the 1960 on pistons have a much better shape and I was wondering if I could modify the 350 head to match that of the later 650 head.
Cheers

Member
User avatar
Posts: 2998
Joined: Mon Jan 01, 1990 12:00 am
Location: HAMPSHIRE UK

Re: '59/60 Cylinder heads

Postby ajscomboman » Mon Oct 15, 2018 6:57 pm

Martin.S wrote:Can anyone explain to me the difference in the pre and post 1960 cylinder heads? The spigot diameters are 0.060" bigger on the later heads but what of the shape of the combustion chambers and their roof heights?
I'm asking because the '59 pistons fit into the 350cc lightweight but the 1960 on pistons have a much better shape and I was wondering if I could modify the 350 head to match that of the later 650 head.
Cheers


The shape of the piston is totally different plus the later 60's piston protrude above the top of the barrel where as the 59's don't. Trying to fit the latter pistons will require considerable machining to allow for valve clearance. The crown may well also need to be reshaped. The 59's will go straight in with only the skirt requiring modification to clear the flywheels. The original 350 L/W pistons are flat top the 59 twin domed, the dome raises the ratio by a small amount and gives it a fair bit more get up and go without stressing anything.

Member
Posts: 6679
Joined: Wed Sep 01, 2004 12:00 am
Location: WEST SUSSEX UK

Re: '59/60 Cylinder heads

Postby SPRIDDLER » Tue Oct 16, 2018 1:28 pm

I know now't about twins but is this '59/60 G12 piston identification write-up from the 'Tech articles' section with drawings and dims any help?

http://www.jampot.com/article_read.asp?id=23
I poke badgers with spoons.

Member
User avatar
Posts: 398
Joined: Sun Mar 18, 2018 12:02 pm
Location: Bristol UK

Re: '59/60 Cylinder heads

Postby Martin.S » Wed Oct 17, 2018 8:38 am

Thanks for you advice there chaps but I'm aware of the difference in the pistons and that a '59 piston fits but it is rather old hat.
What I want to know is the difference in the shape of the combustion chamber in the heads, I read that the ports had changed to make the incoming charge swirl and that the roof height was shallower - by how much I don't know.
Cheers

Member
Posts: 3154
Joined: Sun Jan 01, 1995 12:00 am
Location: ESSEX UK

Re: '59/60 Cylinder heads

Postby G15 Roy » Wed Oct 17, 2018 12:25 pm

Looks like the best thing to do is buy a 1960 650 head they are always some for sale at the Kempton jumble
Roy

Member
Posts: 498
Joined: Mon Jan 01, 1990 12:00 am
Location: NORTHAMPTONSHIRE UK

Re: '59/60 Cylinder heads

Postby raffles » Wed Oct 17, 2018 6:12 pm

There will be a man from Essex who will no doubt sell you one
Tony

Member
User avatar
Posts: 398
Joined: Sun Mar 18, 2018 12:02 pm
Location: Bristol UK

Re: '59/60 Cylinder heads

Postby Martin.S » Thu Oct 18, 2018 11:42 pm

Roy and Raffles - most helpfull - thank you.
Now is there any one who might be able to give me a more technical answer ?

Member
User avatar
Posts: 907
Joined: Fri Dec 09, 2011 5:33 pm
Location: Irene Gauteng SOUTH AFRICA

Re: '59/60 Cylinder heads

Postby robcurrie » Fri Oct 19, 2018 1:49 am

I made some measurements and a CAD model of the 650 cylinder head combustion shape when I was calculating the compression ratio of my '62 CSR. The chamber and the piston tops are hemispherical, just the pistons tops are sliced off (at different heights for various compression ratios) to form a combustion space. The pistons are also pocketed for valve clearance. I will try to post some section views as soon as I get home from hospital early next week.

Rob C

Member
User avatar
Posts: 398
Joined: Sun Mar 18, 2018 12:02 pm
Location: Bristol UK

Re: '59/60 Cylinder heads

Postby Martin.S » Fri Oct 19, 2018 7:52 am

Thanks Rob - That would be most helpful.
Hospital? - hope all is OK.
Cheers

Member
User avatar
Posts: 907
Joined: Fri Dec 09, 2011 5:33 pm
Location: Irene Gauteng SOUTH AFRICA

Re: '59/60 Cylinder heads

Postby robcurrie » Fri Oct 19, 2018 8:28 am

I had a bit of an accident (all by myself) on my CSR and rode over a badly marked and lit traffic island. Woke up in hospital with a broken leg, foot, heel and pelvis. It will take a while to get the CSR healthy again as well.
Cheers

Rob C

Next

Return to G12 / AJS Model 31

Who is online

Users browsing this forum: Google [Bot] and 10 guests