BN4 cylinder head casting change date?

[57_BN4]

Would anyone happen to know what the change date for the BN4 head casting was?

My car BN4O40559 came with an AEC271 head which has some cracking between the cooling passages and I have an AEC666 head off an A105 sedan which is in much better condition. I'm wondering what the car would have had originally.
The pics on Healeydata.com would suggest somewhere around BN4x30000 the head changed which would make the head which came with the car incorrect.

BN4L27518 AEC271
BN4L28224 AEC271
BN4LO29704AEC271
BN4LO29752 AEC271
BN4LO30601 AEC666
BN4L36686 -looks like AEC666 but hard to tell from pic
BN4O43177 AEC666
BN4LS48441 AEC666
BN4L48491 AEC666

The main visual difference between the castings is the addition of a brass blanking plug between cylinder 5&6 on top of the intake gallery.

 

[dougie]

The change was made on some cars starting in October of 1957 with BN4 - 48863 and all cars received the upgraded head by November 1957 with 52602.

 

[57_BN4]

Hi Dougie,

Thanks for the information. Are you referring to the separate-manifold head or the two versions of the gallery head? I'm just talking about the gallery heads only.

The workshop manual has drawings depicting both earlier and later gallery head for detailing different aspects of engine repair but it doesn't specifically identify one from the other or even mention any difference.

compare this pic with the one above, the brass hexagon plug at the back of the gallery is missing from this earlier head

Cheers,
Andy.

 

[dougie]

Yes, I'm referring to the introduction of the 6-port "MM" head. There is no documentation that I'm aware of that distinguishes between the differences in the early BN4's gallery head you've described.

 

[red57]

Probably no help but mine is BN4L037229 and it came with an AEC666 which I think was original.

Dave

 

[57_BN4]

Hi Dave,

Thanks, that agrees with the Healeydata information

Andy.