Head Identification

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

Postby Martin.S » Mon Aug 13, 2018 11:26 pm

Oh that is confusing as I read

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


was for the 350 lightweights and that

Prewar
Information relating to Matchless and AJS Models built prior to 1939


was for Pre war stuff - most confusing

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Re: Head Identification

Postby Ozmadman » Mon Aug 13, 2018 11:31 pm

clanger9 wrote: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) have the same "fat" exhaust valve guide.
All 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.

Do you mean the fat exhaust valve, not guide? It was a mod for the early 350's as well. My (1960) model 8 had the early thin stem exhaust valve and I fitted the later guide and "fat stem" valve..
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1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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Re: Head Identification

Postby Ozmadman » Mon Aug 13, 2018 11:42 pm

Martin.S wrote:Oh that is confusing as I read

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


was for the 350 lightweights and that

Prewar
Information relating to Matchless and AJS Models built prior to 1939


was for Pre war stuff - most confusing

You are correct in my opinion...
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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Re: Head Identification

Postby clanger9 » Tue Aug 14, 2018 7:02 am

Ozmadman wrote:Do you mean the fat exhaust valve, not guide? It was a mod for the early 350's as well. My (1960) model 8 had the early thin stem exhaust valve and I fitted the later guide and "fat stem" valve..


My bad - you are correct. I misread the columns. I should have said "1960 Lightweights have a thinner exhaust valve stem. Later ones have a fatter stem."
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: Head Identification

Postby clanger9 » Tue Aug 14, 2018 7:06 am

Martin.S wrote: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?


According to the manual: "As the inlet valve head diameter is larger a new type cylinder is used, which can be used on previous 250cc engines"
1966 AJS Model 14 250 CSR "cafe racer"
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Re: Head Identification

Postby Rob Harknett » Tue Aug 14, 2018 9:42 am

Martin.S wrote:Oh that is confusing as I read

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


was for the 350 lightweights and that

Prewar
Information relating to Matchless and AJS Models built prior to 1939


was for Pre war stuff - most confusing

I'm puzzled? If I click on the house Icon I see a list of Topic subjects one being G5/Model 8. That's all. I do not see ..Information relating to the Matchless G5 or AJS Model 8 350cc Lightweight.
Errors and confusion can creep in when a year is not given. Which is why manufacturers insisted on one giving year and model. G5. 500 SV introduced 1937. Model 8. 500 OHV introduced 1926. G5 / Model 8 350 OHV ( Lightweight ) re introduced 1960, would avoid confusion as year and model is stated.

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Re: Head Identification

Postby Rob Harknett » Tue Aug 14, 2018 10:07 am

If you click on g5/mod 8 Eamonn has made some postings, the first being " Watch out for " add comments. Maybe I should add a comment, drawing attention to the pre war G5 and Mod 8. Most confusing is the AJS model 7, introduced 1926 as 350 G7 and GR7. This model prefix changed every year before it settled for 7R in 1937. Yet for all years, people still seem to refer the model as 7R and introduced in the post war era. I did do an article in Jampot on the time line and years of the various changes of year code letter prefixing 7, for Wolverhampton AJS, Last 2 digits of year prefixin 7 for AMC AJS, in the through 30's until it finally became in 1937 just 7R onwards into the post war era.

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Re: Head Identification

Postby alanengineer » Tue Aug 14, 2018 2:45 pm

I thought the lightweight 350 and 250 csr had decompressors in the head and the standard 250 was left without

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Re: Head Identification

Postby clanger9 » Tue Aug 14, 2018 5:01 pm

alanengineer wrote:I thought the lightweight 350 and 250 csr had decompressors in the head and the standard 250 was left without

Good point! The parts list has the answer:

350 and 250CS (all years) - decompressor fitted
250 and 250CSR (all years) - no decompressor
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: Head Identification

Postby Ozmadman » Wed Aug 15, 2018 8:55 am

The decompressor only affects the type of rocker cover and not the head and TBH you don't really need it for the 350 anyway with its 6.9:1 low compression!!
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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