Hello,
I am working on my BSA.

I found out that there are two different sizes cylinder heads,I have two cylinder heads. One does have more broken fins then the other.
I think the right one is the original and the other?
To which belong the other one?
Can be there a different in speed or compression?

email (option): bsa-m20@libero.it

Hi Richard...The head on the left is the early pattern of the '10 bolt' cylinder head which retained the combustion chamber shape from the early '8 bolt' engines (no. of cylinder head bolts)...

The head on the right is the one that replaced the one on the left and had a slightly improved combustion chamber shape/squish area...

Both heads have the same combustion chamber volume despite looking different so either will give the same compression ratio...

The later head would be the best choice but in practice the engine will run OK with either..
However, the available head gaskets (use a solid copper one) will fit the later head better, following the edge of the combustion chamber more accurately so I would go for that one if the fins are reasonable.......Ian

Thanks Ian,

I will try them both to see what is the different in speed or Hills.
Must be a reason why they have changeged the curve inside.

email (option): bsa-m20@libero.it

Hi Richard, I would say the changes were made primarily to improve combustion and to a degree cylinder filling (gas flow)....Don't hold your breath for a massive performance jump though...Probably it will go from very slow to very slightly less slow.. ...
The war only took 6 years because it took everyone 18 months to get there...Ian

And here's the third shape to give you 10mph faster!!

Hello Douglas,

Very nice work.
Welding iron is very difficult I have heard.
It can cracking with welding and with high compressing under your cylinder head you arrived at 200kg or more inside.
But I am not sure about the kg but the compres is very high.

Richard

email (option): bsa-m20@libero.it

It was just mig welded with no preheating or preparation. Easy as.