Author Topic: Alloy Cylinder head - A7ss for A10?  (Read 1489 times)

Offline nigeldtr

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Alloy Cylinder head - A7ss for A10?
« on: 14.07. 2010 22:11 »
Does anyone know if a A7ss (671122) cylinder head can be used on a 650 GF?

Thanks

Nigel
1951 Golden Flash (engine now rebuilt) 1953 M21 a pain to start and 1961 GF that is turning into a black hole!

Online bsa-bill

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Re: Alloy Cylinder head - A7ss for A10?
« Reply #1 on: 15.07. 2010 09:26 »
there are stories off A7 alloy heads being used on A10's for racing (to lift compression), don't know if I would like to do it for a road bike though, racing being a different ball game ( never that far from pits and a push)
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online muskrat

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Re: Alloy Cylinder head - A7ss for A10?
« Reply #2 on: 15.07. 2010 09:29 »
G'day Nigel,
                    Yes but !! With the bore being smaller there is a ridge that can be removed to mate the head with the barrels. Place an A10 head gasket on the head and scribe around the bore holes. Remove the alloy with a dremmel to blend in with the combustion chamber. Larger A10 valves can be fitted with some work on the seats.
That's a '54 A7 head on the 650 cafe.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline Rocket Racer

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Re: Alloy Cylinder head - A7ss for A10?
« Reply #3 on: 15.07. 2010 09:55 »
I concur with Muskrat, If you're running flat top pistons you dont even need to modify the combustion chamber shape.
The twin port head that was supplied on my A10 basket case turned out to be a reshaped 500 head to run with 10.5 pistons. But was still small valve though had been ported.

A good mate is running a stock alloy A7 head on his gold flash flat tops.
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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Offline nigeldtr

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Re: Alloy Cylinder head - A7ss for A10?
« Reply #4 on: 15.07. 2010 21:47 »
Thanks very much for the picture and information. I have a GF so looks like it should be straight forward.

Kind regards

Nigel
1951 Golden Flash (engine now rebuilt) 1953 M21 a pain to start and 1961 GF that is turning into a black hole!

Offline A10Boy

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Re: Alloy Cylinder head - A7ss for A10?
« Reply #5 on: 16.07. 2010 11:11 »
Ideally, any work which affects the volume of the combustion chamber needs to be done by a machine shop as the two chambers need to be identical in volume. They can measure volume and match them.
Regards

Andy

1960 A10 - Black Golden Flash
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Online muskrat

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Re: Alloy Cylinder head - A7ss for A10?
« Reply #6 on: 16.07. 2010 11:21 »
That is true Andy. I CC'd the chambers before assembly. 31.12cc and 31.15cc close enough. Just under 10.5:1.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7