Cylinder head

[spike123]

Hi all
Can anyone tell me which casting number I need for a 1972 cylinder head for my thunderbird
Cheers

[Spaceman]

1972 Thunderbird cylinder head is part number 71-2307

[spike123]

Is that the casting number

[Spaceman]

In a lot of cases, the number cast into a BSA casting is just the catalogue part number but I am not sure this is the case with a cylinder head. It would help if you explain why you need a casting number? If you are simply looking to source a 1972 A65T cylinder head, I wouldn't have thought you would need a casting number for this purpose?

[Ian C]

The casting number for the Thunderbolt cylinder head is :- 71-2200

[spike123]

The reason I'm asking is I'm not sure if the valve size changed with the years, I'm putting a 750 cc conversion, so I'm wandering if any head with 3/8 holdown bolts would do

[Mike Farmer]

 

Hi
I'm a bit hazy on this one but I'm think the valves changed late 60's. I've been down this road but back when etc. Guessing that the head may not have had to change if larger valve seats was sufficient. Sorry cant be of more assistance. Ask SRM they should be able to  give you the 'gen'

Mike

[DAVE BRADY]

Hi,

If I remember correctly when people fitted big bore Devimead 750 kits they did not change anything.  So I suppose the idea was to run the engine with what it came with.  For racing then big valves etc, were fitted.

Dave.

[Mike Farmer]

 

I took this up with SRM a while back when I was considering it. That was defo their stanpoint. Just use the head a fitted. I am still trying to find the info re valve sizes.

Let ya no.

Mike

[Mike Farmer]

 

Ive just had a look at drags site and the valve Pt-No's change somewhere between 1963 and 1966. But it doesnt give detail. In my mind the later ones where about +040" larger diameter. That would suggest a head casting change. Dunno.

Somewhere I have full detail but that is somewhere??

Mike

[idie]

I believe that the A65 around 64 -65 had bigger valves for one year, it seems that it wasn't very successful and they reverted back to the previous size. I'd will have to try and find where I saw the information.

[JulianS]

The inlet valve size increased for 1966 season on, part 68 665, used until the end of production..

[Mike Farmer]

 

Hi Julian. Thats brill, in fact I think I got the info from you many moons ago prob 2017 or 18. Now we know.

Mike