A7 to A10 head?

A friend of mine has an A10 with the iron head. He has recently picked up a ally head for an A7, part number 67-1122. Do any of you BSA experts know if the same basic casting was used for 500 & 650? I put it side by side with his 650 iron head & the inlet port is the same size, but the diameter of the combustion chamber is 66mm as opposed to 70mm, & the valves are smaller. Whilst I can open the CC up to suit the bigger bore, I'm not sure if it would be wise to open up the seats much bigger.
If any of you have done this please let me know your thoughts.

Matchless said:

A friend of mine has an A10 with the iron head. He has recently picked up a ally head for an A7, part number 67-1122. Do any of you BSA experts know if the same basic casting was used for 500 & 650? I put it side by side with his 650 iron head & the inlet port is the same size, but the diameter of the combustion chamber is 66mm as opposed to 70mm, & the valves are smaller. Whilst I can open the CC up to suit the bigger bore, I'm not sure if it would be wise to open up the seats much bigger.
If any of you have done this please let me know your thoughts.

Click to expand...

I've not done it myself but I believe it's quite a common conversion
My mate bolted a standard alloy A7 head straight on to his A10 but I cannot remember if he had concave pistons or not
The bike ran really well

https://www.a7a10.net/forum/index.php?topic=10457.0
You may have already seen this,but there's some info here

baz said:

https://www.a7a10.net/forum/index.php?topic=10457.0
You may have already seen this,but there's some info here

Click to expand...

Hi Baz, thanks for posting, that's very interesting.
From the part number, do you have any idea what model of A7 it's from?,

Matchless said:

Hi Baz, thanks for posting, that's very interesting.
From the part number, do you have any idea what model of A7 it's from?,

Click to expand...

No sorry
I'm not that up on them
Luckily I picked up a road rocket head for my A10 many years ago
But at the time I was considering an A7 head after seeing how well my mates one ran

Put an A7SS onto the outfit (big wheel sidecar) that we used to race so I could fir two carbs. Ran a dremel around the edge of the combustion chamber to smooth it out and make ups some of the difference in bore. (Also machined out the valve seats to take Road rocket valves) Engine gave over 50 horse at the back wheel on ordinary petrol.
Go for it!

SStewth . A Squish Band A 10 Head !

The olde dunger ran 10: 1 domed pistons , 53 A10 . so the valves rebaed themselves innt iron ead ,
The loose baffle came out easilly . Matching that took the rest of the day . Ran a 16.9 & 80 like a new one would.
Tho it did seem ter , thinking I could RUN faster , while doing it . 1/4 mile car club sprint .

Those doomed pitons youd get a good 11:1 C. R. with THAT head . Id only remove sharp edge / deburr .
as incandesent edges preignite . As it got manwell adsvance ?

Ancient Uncle has 600 SS Ign. notched for ' correct ' . Through the gate ' for tyre smoking gettaways . was D. R. ,
Wasnt going to get caught by a messerschmidt again .

std. valves'd be ' ralley tune ' - tourque . Big Valves required for Full Race and 10.000 r.p.m. .

If you think your cranks cracked , hit it with a Hammer . If it RINGS while youre belting it around the lawn , it wernt ! .