Have raised this before, but had no definitive solution.
Not sure why they are different combustion spaces.

My main query is, if I use the one with some fins missing, (one on the right- both pics)what is the limit before it is classed as scrap? Can probably get some rebuilt, cast welding done. But just wondering if these would be near the limit, seems not to be a third of the fin cooling area at present?

This is my Cast iron head, along with the spare cast iron head.



This is the tops of each.



This picture was with my spare Alloy Cylinder head, alongside the unusual combustion chamber Cast cylinder head. It seems to me that the odd one is the one on the right of all the pics. For those who notice, the plug holes are filled with putty so I could check the actual cc of the combustion area, they are the same. However it does look like it will create a different movement of the combustion gases. Not sure what benefit it has.

The chamber of the head on the right is the earlier pattern...This was 'inherited' from the early '8 bolt' M20 engine and was used on early '10 bolt' engines...

The iron head on the left and the alloy head are the later pattern. The alloy head was introduced in '51 but the iron version was used during the war as well as the change was made just before or very early during the war...

It's fair to assume the later pattern head has the better shape with regards to combustion which was more than likely the reason for the change being made...Ian

email (option): ian@wright52.plus.com

Thanks Ian.
SO I might be ok using the later iron type head. But has it enough fins for cooling, just worried about enough cooling with fins missing.

Paul C

A good welder/brazer should be able to fix this. Its a bit time consuming as the fins taper at the top.

Bit of a labour of love; so might be a bit expensive for a really good job.

I had an old guy do some fins on an A10 for me about twenty five years ago. Once painted you could not tell at all!

I have some fins broken on my head (iron) and have run it for years like that - some long runs too!

email (option): sacombsashtrees@hotmail.com

I know at least three welder guys around me who have all repaired or replaced fins for me over the years. Ron

email (option): ronpier@talk21.com

To be clear...The head with the missing fins is the early one....The one on the right in the pictures...

The later one is the one to use...Ian

email (option): ian@wright52.plus.com

Paul C

Have raised this before, but had no definitive solution.
Not sure why they are different combustion spaces.

My main query is, if I use the one with some fins missing, (one on the right- both pics)what is the limit before it is classed as scrap? Can probably get some rebuilt, cast welding done. But just wondering if these would be near the limit, seems not to be a third of the fin cooling area at present?

This is my Cast iron head, along with the spare cast iron head.



This is the tops of each.



This picture was with my spare Alloy Cylinder head, alongside the unusual combustion chamber Cast cylinder head. It seems to me that the odd one is the one on the right of all the pics. For those who notice, the plug holes are filled with putty so I could check the actual cc of the combustion area, they are the same. However it does look like it will create a different movement of the combustion gases. Not sure what benefit it has.

email (option): dharmanugroho@yahoo.com

My M21 head has way less fins than that, seems fine in use and doesn't overheat. I did think about replacing some fins but it's never been a problem.

email (option): jeremy@clogmaker.co.uk