Head Identification

Information relating to the Matchless G5 or AJS Model 8 350cc Lightweight
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Head Identification

Postby Martin.S » Mon Aug 13, 2018 5:51 pm

I've bought what was advertised as G5 parts but the Barrel, crank and rocker box is G2 , the head I'm not sure about. Its exhaust guide has a bigger bore than the inlet, the inlet tract measures 1 1/16"at the carb face. There is a stamping on the under side - 3 RE 61. Does any one have any idea what this head is - 250 - 350?
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Re: Head Identification

Postby Rob Harknett » Mon Aug 13, 2018 5:59 pm

Could answer that easy if it was a pre war G5 & G2. But guess its a post war light weight so will pass.

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Re: Head Identification

Postby SPRIDDLER » Mon Aug 13, 2018 6:50 pm

Your Profile doesn't give any details (e.g. year) of your bike. I don't know if they differ year to year.
A Lightweight officianado will no doubt be along but just an idle thought.......
Does the head (witness marks etc.) match your 250 cylinder?
250 Bore 2.75"
350 Bore 2.8345"

http://archives.jampot.dk/book/Owners_m ... Manual.pdf

Its exhaust guide has a bigger bore than the inlet,

They all seem to use the same inlet valve guide but different exhaust guides for the 250 and 350's.
From the Spares List here:.........
http://archives.jampot.dk/book/Spares_l ... s_List.pdf
LW valves and guides (640x299).jpg
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Last edited by SPRIDDLER on Mon Aug 13, 2018 7:26 pm, edited 4 times in total.
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Re: Head Identification

Postby clanger9 » Mon Aug 13, 2018 7:13 pm

What size is the inlet valve? 350 and 250CSRs have a 1.6" inlet valve (OK, 1 19/32" if you are fussy). The inlet tract is 1 1/8".
Normal 250s have a smaller inlet valve and a 1 1/16" inlet tract.

I don't think there's much (any?) difference between the 350 and 250CSR head.
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: Head Identification

Postby Martin.S » Mon Aug 13, 2018 8:34 pm

Rob Harknett wrote:Could answer that easy if it was a pre war G5 & G2. But guess its a post war light weight so will pass.


Hey Rob - that's why I asked the question on the Lightweight sectection!

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Re: Head Identification

Postby Martin.S » Mon Aug 13, 2018 8:42 pm

Spriddler, It's just an assembly of parts (I love a good jigsaw) and the head has been blasted.
Valve guides - The CSR isn't listed (or is that the CS?)and what was the date of that list? I have read somewhere on here I think that one of the CSR's updates was a larger valve stem.
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Re: Head Identification

Postby clanger9 » Mon Aug 13, 2018 8:54 pm

Have a look at the supplementary parts list - it includes the CSR:
http://archives.jampot.dk/book/Spares_l ... o_1966.pdf

You can see that all models (apart from the very earliest 250s and 350s) have the same "fat" exhaust valve guide.
Later models - regardless of capacity - have a "thin" inlet valve guide. 250s have a smaller valve than the 250CSR & 350.
350s and 250CSRs are more or less identical in the cylinder head department (i.e. bigger inlet valve, bigger inlet tract). Main variation is the late model CSRs have coil valve springs and blanked-off oil feeds.
Other than that, there's no difference on the casting that I know of between the 250CSR & 350 head.

[edit: corrected description of which models have the thin exhaust valve stem]
Last edited by clanger9 on Tue Aug 14, 2018 7:03 am, edited 1 time in total.
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: Head Identification

Postby SPRIDDLER » Mon Aug 13, 2018 9:55 pm

Martin.S wrote:Spriddler, It's just an assembly of parts (I love a good jigsaw) and the head has been blasted. Valve guides - The CSR isn't listed (or is that the CS?)and what was the date of that list?

I don't have much first-hand experience with Lightweights :oops: . I just browsed Christians Archive in an (evidently failed) attempt to educate myself before dinner whilst waiting for Williams to decant the rather decent 2009 St Emilion. ;)
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Re: Head Identification

Postby Martin.S » Mon Aug 13, 2018 10:08 pm

OK thanks chaps, So larger valves could be fitted as I presume the seats were the same just cut out bigger.
Are we sure the tracts are the same size as the carbs?

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Re: Head Identification

Postby Rob Harknett » Mon Aug 13, 2018 10:56 pm

Martin.S wrote:
Rob Harknett wrote:Could answer that easy if it was a pre war G5 & G2. But guess its a post war light weight so will pass.


Hey Rob - that's why I asked the question on the Lightweight sectection!


But there is no light weight section Martin. It's G5 /mod 8 see above. There was pre war G5, G2 and model 8. However, we usually look at G5 mod 8 as being lightweight 350. Occasionally a person may just refer to a model not stating the year that could be for a pre war machine. I often get people ask me for help in reverse to that. So I am thinking pre war, but it turns out they have a post war model. Always good to state year and model, AMC factory insisted on this info years ago with reference to it in parts list introduction. It could make a difference in you getting a correct reply. There were very few yearly changes in the 350 lightweight. I only know of 2. stronger gear change spring and longer kick starter, introduced on the last 1962 model. But the book I have that gives reference to yearly changes made, lists every change made.

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