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This may be a stupid question but Ive uncovered a cylinder head that has some numbers stamped into it .....12G938 Its got truly beutiful porting on it also the number 50 which is spaced above/over 18.6 , which is over 18.2, which is next to 5240...The head is dowled for the manifold....I will try and post some piccies this evening.....but does anyone know what any of the markings mean ?

Mick

wasn't the 12G938 the head casting that the 'the one to have' in the 1970's for a starting point for a performance head

sounds like a nice find!

Sound like Downton to me. Pic's!!!!!!!

Cylinder Head Specs And Part Numbers



Part Number Inlet Diameter Exhuast Diameter Norminal CC Standard Fitment
Inch MM Inch MM Cubic Capacity
2A628 1.0625" 26.99 1.00" 25.4 24.5 850, 998 Mini & 948 Sprite

2A629 1.0625" 26.99 1.00" 25.4 24.5 948, A35 & Morris Minor

12A1456 1.0625" 26.99 1.00" 25.4 24.5 850, 998 Mini & 948 Sprite

12G202 1.156" 29.36 1.00" 25.4 26.1 997 Cooper, Austin 1100 Mk

12g206 1.218" 30.93 1.00" 25.4 28.3 Early 998 Cooper, MG1100

12g295 1.218" 30.93 1.00" 25.4 28.3 998 Cooper, MG1100

12A185 1.401" 35.6 1.22" 31 21.4 Early Mk1 Cooper S

AEG163 1.401" 35.6 1.22" 31 21.4 Late Mk1 & Mk2 Cooper S

12G940* 1.312" 33.33 1.15" 29.2 21.4 1275GT, Austin 1300, all late A+ models inc. Turbo

12g940 (12G1805) 1.401" 35.6 1.15" 29.2 21.4 MG1300, 1300GT & Mk3 Cooper S

12g940 1.401" 35.6 1.15" 29.2 21.4 MG Metro Plus Above.

CAM4180 1.0625 26.99 1.00" 25.4 25.5 998 Mini - A+ (1980-on) and lead free



Not on this list I have for cylinder head specs

right then sorry about the quality but here goes.....And sorry but I forgot to measure the valve sizes...but the work is very very well done...

The 938 was a special thicker casting, which allowed the likes of Downton to modify them further than the 940.

I'm 99.99% certain that those stamped, like yours, 12G938 are (or at least) started off life as a stock low end 1275 head (ie, non Cooper S). If I recall, Part Number 12G938 was a bare head, machine, and fitted with guides, drilled for 9 studs only, valves seat cut were to suit 1-5/16 and 1-5/32" valves. They used one of the 12G940 castings. Around the time these were done, the Cooper S Head that was based on the same 12G940 casting was Part Number 12G1805. Don't confuse Part Numbers with Casting Numbers! I do wish they'd used a more clearer system for IDing thier castings, I've come across no less than 7 distinctly different 12G940 castings, with the later ones having a thin deck.

In this case, clearly from the other numbers and the work done on it, is something else now.

Something very nice indeed Nice find.

12G938 is an id mark that was pressed into the head to identify its destination.Such numbers are an engineering requirement to comply with British Standards.The supplier that the part was destined for would also have to be BS registered and under licence to B.M.C. When the licence supplier carried out there work they would also add a mark to i.d work had been completed has the licence holder would also after be registered with British standards and would be required to conform to the same rules.
!2G940 heads where cast with a thicker deck for special tuning .Downton Engineering Works would of received the head from B.M.C.as they where the only one under licence.
The reason i know this to be true,because many years ago my Farther had a temporary job working for British standards and he would have to carry out compliance audits,he also sourced one of these heads for me and explained all this to me when i questioned its authenticity. The number 12G938 pressed into the head is very small,precise and set deep into the head as they used a big press to stamp it in.This operation would be very difficult to copy,and is a great way to identify a special tuned head.
Hope this helps

Now I must apologise again...early stuff is not my strong point (1990 rover cooper mainstream owner) so is it possible that because of the B.S. standards compliant markings....this has been sorted by a well connected tuning house ? the ports are very very precise and are extremely smooth ,obviously precisely polished,not mirror polished.. but to a very high standard that I've simply not come across before,the edge where it would meet the gasket and manifold is very crisply done and matches the manifold and gasket.

So who could be the most likely producer of this head ?


Mick

china wrote:12G938 is an id mark that was pressed into the head to identify its destination.Such numbers are an engineering requirement to comply with British Standards.The supplier that the part was destined for would also have to be BS registered and under licence to B.M.C. When the licence supplier carried out there work they would also add a mark to i.d work had been completed has the licence holder would also after be registered with British standards and would be required to conform to the same rules.
!2G940 heads where cast with a thicker deck for special tuning .Downton Engineering Works would of received the head from B.M.C.as they where the only one under licence.
The reason i know this to be true,because many years ago my Farther had a temporary job working for British standards and he would have to carry out compliance audits,he also sourced one of these heads for me and explained all this to me when i questioned its authenticity. The number 12G938 pressed into the head is very small,precise and set deep into the head as they used a big press to stamp it in.This operation would be very difficult to copy,and is a great way to identify a special tuned head.
Hope this helps

that's very interesting, I had never even thought about any legal requirements of part stamps

however, you don't need a big press to stamp the neat little numbers, you can either use a large, bench mounted pryor anvil stamp (you basically whack the press with a hammer (or it may be electric) to get it to operate - which is what you would use if you where doing large batches of stuff) or a smaller hand held pryor anvil with the removable letter - I use one of these to number the new Minispares Arden heads up, and as long as you use a locating plate you get a nice, deep consistent 'stamp' of numbers from it.


obviously, in the photos of the head above, the stamps done by whoever has done all the porting etc have just been free stamps, that's why they are wonky - its the 12G938 that has been anvil stamped

Rich you are probably right,different types of tooling is not my strong point,however the 12G938 stamping does look authentic to me and i reckon would be very difficult to copy.There should also be a letter or a number hand punched underneath the stamping and i can remember my dad telling me that this is a mark to identify the work had been carried out by either a certain production line or a certain shift or an individual operator,and should of left a paper trail which i suspect along with many other types of documentation no longer exits.
So for me to identify a 12g940 Downton head i would be looking for one of these stamps and the quality of it. ( You can just tell if you know what i mean)

china wrote:the 12G938 stamping does look authentic to me and i reckon would be very difficult to copy.

it wouldn't be as hard as you think, if the font is a standard Pryor one, then you could just use the individual letters in a hand anvil

if it was a unique font, then its possible to get Pryor to copy it, but you would get it made as a 'one hit block' that would fit into the hand anvil (as there would be no advantage to having single letters) - it would cost a couple of hundred quid for the stamp to be made.

i use a lot of these at work!

Rich again you are probably right.You would think the leg lifters of this world, would realise that it far cheaper to buy an original item than spending thousands of pounds to try and fake them.

china wrote:Rich again you are probably right.You would think the leg lifters of this world, would realise that it far cheaper to buy an original item than spending thousands of pounds to try and fake them.

this is why we unique stamp and numerical stamp a lot of stuff at work

it certainly helps with QC and batch control

ive got a 'fair investment' in specialist stamps, that's for sure

The heads I have found over the years that have been worked are marked as to how much was machined from face and chamber CCs. Some have a serial number for the records. Steve (CTR)

OT: Rich any chance someone from MSC will attend the 55th race at Mid Ohio Sports Car Course next week? I met KD there for the first Sprite Mini Challenge race 20 years ago. I think he took a break from playing golf to run up from Fla.

I think my Slark head is the same casting number, I can't check it as it's up at Southam at the moment , Simon mentioned midgets as original fitment I think ?

CooperTune wrote:
OT: Rich any chance someone from MSC will attend the 55th race at Mid Ohio Sports Car Course next week? I met KD there for the first Sprite Mini Challenge race 20 years ago. I think he took a break from playing golf to run up from Fla.

sure, send me a ticket and I will be there

Thanks for the help Lad's

Mick