Help with twin exhaust header pipes.

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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SOHC
Posts: 36
Joined: Tue Mar 07, 2017 11:04 pm
Location: Newzealand

Help with twin exhaust header pipes.

Post by SOHC »

Hello.

Helping a friend rebuild his 1959 650 twin, it has a Siamese exhaust on it but he wants to fit a duel exhaust, but we are unsure what heads it has as there seem to be a few different types.

Our engine has embossed

Head: 026053

barrel: 025040

and the stamping on the case is 59/31x0762

if someone could give us the part numbers for the right pipes would be highly appreciated.
Don Madden
Member
Posts: 2882
Joined: Mon Jan 01, 1990 12:00 am
Location: USA USA

Re: Help with twin exhaust header pipes.

Post by Don Madden »

The engine has mixed parts. The barrels have a 1959 part no. with 3in top spigot & the heads 1960-up with 3-1/16in. recess for the spigot. I don't know what pistons but 1959 pistons are compatible only with 1959 heads. Before trying to solve the pipe issue, change the top end so that Cylinders, heads & pistons are all 1959 or all 1960-up. Regards, Don.
Rangy65
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Posts: 433
Joined: Tue May 07, 2013 11:35 pm
Location: LINCOLNSHIRE UK

Re: Help with twin exhaust header pipes.

Post by Rangy65 »

Hi there, i am also having header pipe issues. My bike is a Mod 31 1959 with original heads & barrels. The 59 heads are different to the 1960 onwards/CSR.

The usual manufacturers of the header pipes in the UK have run out and can't tell me when they will manufacture any.

I enquired if i could use the 1960 pipes they said that the angle of the exhaust port is different on the 59 model.

So i would say that if your bike has the later heads ( these have cross finning on the bottom fin) then you could fit the G12/Model 31 pipes ffom 1960 onwards.

Alternatively decide which silencers you like best - Matchless or Ajs ( different) and get some headers made up to suit. ( there seems to be lots of fabricators in the US).

Hope this makes sense.

Steve
SOHC
Posts: 36
Joined: Tue Mar 07, 2017 11:04 pm
Location: Newzealand

Re: Help with twin exhaust header pipes.

Post by SOHC »

Hello, thank you for your help, I will check the spigot tommrow morning, the bike did have a blowing head gasket


Yes heads have the cross fins under the exhaust ports.


Funny enough my job once was sand bending exhausts for Nortons,
SOHC
Posts: 36
Joined: Tue Mar 07, 2017 11:04 pm
Location: Newzealand

Re: Help with twin exhaust header pipes.

Post by SOHC »

The heads are loose on the barrel spigots and the spigot holds the gasket faces apart by about 30 thou but the head gasket is nearly 2mm thick. I gess it has the 1960 pistons in it as they seem to match the combustion chambers
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