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MG MGB Technical - Cylinder Head, what have I got?

Bretheren, My '66 B is original spec in most respects, & I confirmed 5 yrs ago on purchase that the block was an 18GB from the casting date. It had been painted black so I recently repainted it by hand original maroon, happy with results. Consulting Clausager I noticed I had no Patent No' on the front of the head beside the 'Stat, & then noticed the "shoulders" around front, middle, & rear headbolts on the plug side? This is a late head?
Consulted the Archives on here & MGOC & various sites, mainly American, & concluded mine was probably home market 18V 12H4736.
I removed the R'cover to find; Raised Patent no' to the rear, Raised "1800" & big no;"6" below it, middle section, (no cast date ring) & here comes the mystery; Punched or stamped as if individually as varying depth, "2H4736". The 1 before the 2 missing or so feint i can't see it. Any pics I have seen have that No' clearly cast in raised/ relief lettering, & a cast date ring in the middle section.
What on earth have I got??
I have won prizes with this car. Neither Judges or myself spotted this before. I thought i had a complete original engine.
Baited breath.
Brian.

B. G. Griffin

Sorry to say it sounds like common or garden 12H4736. The casting numbers ground off at the factory and restamped. Could even be a late CAM1106 ground off and stamped 12H4736.
Peter
Peter Burgess Tuning

And Peter, would this have been the original head for this 18 GB engine? Mike
J.M. Doust

Mike, I know now that it's not. 18GB was a Mk1 block circa '64, 65' '66. The 12H4736 was post '75 for 18v blocks.
B.
B. G. Griffin

You should have a 12H906 on your engine. However, B heads are getting scarce, well, I should say uncracked, serviceable B heads are getting scarce, so any 1800 B head is good.MGA suitable heads are even scarcer.

Peter
Peter Burgess Tuning

Peter, I knew that if anybody could enlighten me it would be you. Many thanks for the response. So that was a thing that you have come across, grinding off the raised numbers? I don't need or want to remove the head to see if the block face was ground out to acomodate bigger valves, but from reading, were the original smaller valves not back for that head?
There is a 10 yr gap in the history of the car, so my question is, if the head was to be replaced in say '75 to '80, would a garage be able to order the correct spec head, or just supplied with the "current model" at the time being the 12H4736.
What would be the reason to grind off "CAM1106"?
And finally, is there any chance it's from a Marina or Sherpa?
Regards,
Brian.(who now has no right to be predudiced against Rubber bumpers any more).
B. G. Griffin

I think people tended to fit the first head they could lay their hands on. We supply the correct head if we can.

What year is your block?

Maybe the original build specified 12H4736 so the number had to be hand stamped? Maybe someone in the know will come along and tell us.

At its age I would think you might be looking Princess or Marina....but not willing to lose my beer money laying a bet on it.
Peter Burgess Tuning

Casting numbers are what comes out of the foundry, parts numbers are what you get after it is machined.

CAM1106 is a smog casting, basically for 75-0n US cars, so small valve, and lumps for air injection, water choke etc.

12H4375 is the finished part number for Non-smog heads, made from casting 12H4376. This seems to be the big valve head, 72-74.5 US cars had these but the casting was 12H2923 to include the smog lumps.

So, what you have is a CAM1106 casting substituting for 12H4376, and probably machined to part 12H4375 big valve, or possibly whatever the part number for small valve open chamber non-smog heads was. Should have unmachined lumps for air injection, and no hole at the back for ZS water choke, big valves if you lucky!

Numbers get changed because they "rationalize" things, or because a casting will not meet spec for the casting number on it, but will for another number. Like this could be a case of a defect in the seat made the hole too big to machine for a small valve US head, or the smog lumps were out of spec; but it works fine for a big valve UK one, which would originally/normally be made out of a 12H4376.

Good info here, but we didn't get a bunch of stuff that was floating around the rest of the world, so we got gaps:
http://www.mgbmga.com/tech/mgb25.htm

FRM
FR Millmore

More:

http://www.flowspeed.com/cylinder-ident.htm

FRM
FR Millmore

12H4736 is small valve offset oil feed lump but not drilled as is the cam1106 in the UK. Only 12H2709 and 12H2595 castings are big valve in UK.

Peter
Peter Burgess Tuning

Brian

Hard to tell from the angle, but it looks like you might have '68 - '74 front wings, too.
Dave O'Neill2

Beginning to sound like Johhny Cash's Cadillac song, One Piece At A Time.

Or my grandfathers axe, my Father changed the head and I fitted a new shaft.

Not mant cars are original. Even original seems to depend what was on the shelf when the car was made......take Lotus (Loti?) for example !

Peter
Peter Burgess Tuning

FRM & Peter thanks again Guys, all good info. Dave you are right, I have the receipt from 1983, new wings.
If you are familiar with "Only Fools & horses" Peter, the term "Triggers Broom" has entered the vocabulary. he's the roadsweeper who has had the same broom for 23 years,,,,only had to change the head 11 times 7 the handle 4.
B.

B. G. Griffin

Brian,

That IS a lovely car.

Also, still a lovely lawn. We have the green back in our countryside at last - well, at least that part of it not under water!

Drought and flooding rains (lol)
Roger T

As a matter of interest has anyone come across one of these heads shown in the picture, first time I have seen one. It appears to be the same as the UK74-78 12H4736 non lump head casting. The head number is CAM1758.

Peter

Peter Burgess Tuning

Peter -
C'mon man,
"12H4736 is small valve offset oil feed lump but not drilled as is the cam1106 in the UK."
"the same as the UK74-78 12H4736 non lump head casting"
Yer confusatin' me!

Isn't it remarkable how new stuff turns up 30 years after the fact?

FRM
FR Millmore

It is weird, I havent a clue what the head is off, just turned up on an 18GK engine I bought.

I attach a pic of 12H4736 non lump B head

Peter

Peter Burgess Tuning

Well if you guys are confused, what hope for me??
Peter, you asked on the 2nd what yr was my block, (posted at the start) it's a 5 bearing, cast in 1965, the car is '66. "Original build"? whats that mean?
What is "Non Lump"? Are "Lumps" the "Shoulders" I mentioned? I'll try to get a pic of mine, but rocker gear is in place.
Your Pic @ 8:22 this AM does not show the head bolt shafts, with or witout "lumps".
My first discovery that I had a later head was one thing, but not seeing a similar one in any lineup is causing me concern.

Brian.
B. G. Griffin

Hi Brian

You have a 12H4736 Lump head casting (built up but not drilled for exhaust port air injection), hand stamped at Factory. I attach a picture.

I meant original build as in the 70s not when your engine was built in the 60s, you should have a date stamp cast into your block near sump flange level directly below the oil filter boss.

Peter

Peter Burgess Tuning


As I said above "Numbers get changed ...or because a casting will not meet spec for the casting number on it, but will for another number. Like this could be a case of... the smog lumps were out of spec; "

The last pic is not really a 12H4736 casting, but is a CAM1106 with defective lumps. These make it unsuitable to be drilled for AI, but still good for the intended use of a 12H4736, which does not have the AI lumps. So they grind off the CAM1106 and stamp the 12H4736.

So this should be an open shallow chamber head, which then should require valve clearance notches in the block. By Peter's info, should be small inlet, but could easily have had the big valves fitted.
This car would originally have the closed deep chamber head with small valves and no notches in the block. Probably 12H1326.

FRM
FR Millmore

I dont understand why the lumps are defective?

Peter
Peter Burgess Tuning

Appears to be material missing from the front one at least. Suppose it could be an artifact of lighting, etc.

FRM
FR Millmore

Here is another oddity. The 12H2709 head is associated with 18v CChrome bumper Bs UK 71-74 and Basic Landcrab 1800s and Marina TCs. The 12H2595 which is really a 12H2709 skimmed/milled an extra 20thou is associated with the 1800S spec Landcrab.
Here we have a casting with 12H2709 and 12H2595 cast in, manufactured 1969!

Peter

Peter Burgess Tuning

just to make life even more confusing, the 12H2709 was an inline oil feed non lump head....or was it?

Here we have a picture of a 12H2709 head with lumps cast on for air injection.The casting number is not in the usual place for a 12H2709. It is also cast for offset oil feed but sports an inline drilling!

The oil drilling goes vertical to the head face as with an inline oil feed. If you try and convert an offset feed by blocking the offset holoe and drilling straight down you will most likely find a waterway! We have to drill at an acute angle to meet the original offset hole.

Peter

Peter Burgess Tuning

Guys,
this is becoming esoteric :-))
I start to feel like a complete newbie to the MG-scene, although I own my 64 B since 1978.
I donīt even know the casting # of my head (the one on the engine., that is..) and I have to admit that I never in all these years had the urge to look this up :-).
Still: interesting reading!
Joern-M

In accord with my contention that the casting only has to be suitable for the part to be made, the 2595/2709 makes sense.
The aberrant 2709 looks as if they cored it as 2709, but used some other outside mould box, putting 2709 on because it needs to be machined that way.
I always wanted to saw up a bunch of heads etc., to see what they are like inside. This one would be very interesting to section in the oil feed area, but then you'd need comparison samples.
There is always the possibility that Mr Burgess has got into the silly putty and is making these things!

FRM
FR Millmore

No they are real :)

I have a theory about the lump head 2709. The rocker face at the rear of the head is flat and will accept the drilling and tapping for the water feed for the export single carbie. This head was available in a BL box as a spare part. I have a new one in its original box. The head will actually fit any B series 1800 application, inline oil feed rockershaft, offset oilfeed rockershaft, 71-74 large inlet valve (big valve conversion on small inlet valve head though!, can be drilled for air injection and can be drilled for water take off, a universal B head? The last of the castings? This could coincide with the off load on the market of brand new bare castings about 20 years ago. Our box says 2708 for the head number.

Peter
Peter Burgess Tuning

Ive noted that on a few of the pictures there is a stamp under the block type that reads AF3H What does that stand for?

A pic of my head merely for interest :)

Jamie Shaun Ahlund

Peter -
Excellent theory!

The one number off for part number is consistent with standard practice. I think the part was designed and part/drawing numbered. Then, working off that drawing, a drawing was made of the blank casting/forging required to produce that part, and given the next number. Then it got messy as changes were made, like a revised casting and casting number for a changed part, but still suitable for the original part, which retained its number. The same casting, machined differently, would have a different part number, screwing up the whole pretty sequence. There are parts where the blank is numbered as xxxR/L, which can be machined for either hand. And there are superseded parts which are made differently but retain the original part number.

FRM
FR Millmore

Hi Peter,

Finally after many years the 18V engine is coming together! Tomorrow I will bring the parts to my "Enginefriend". Hopefully the SC will be installed later this Spring

Interesting photos of different Cylinderheads. The one you helped me with once upon a time is a 12H2709 with inline oilfeed as the one on your photo but without the 12H2595, and marked AF4 H instead.

As Jamie asked what does this AF4 stand for. And is it possible to say what year the head is made knowing this and the marks K and 1 in the middle of the head. See photo!

Regards

Anders

T Dahlberg

Hi again,

Could only upload one photo!

Here is another one!

Anders

T Dahlberg

Anders did I see a copy of the Barometern under that Cylinder head? :)
Jamie Shaun Ahlund

The AF4 H etc are likely ID marks for the set of core boxes used to make the casting. The various pieces of patterns and cores are matched to make a set. There could be many sets for a high production part, but the pieces do not interchange, hence the ID. When changes are made, some patterns get changed, but the set retains its identity, possibly with an additional designation.

The round bit is the date code, October xx 71 I think, per the Flospeed link I gave above. The day number is garbled on yours.

FRM
FR Millmore

Hi Anders

Good to hear from you. I am not familiar with the reasons for all the numbers and letters on the heads....I like it best when there is a straightforward day/month/year stamp.

Peter
Peter Burgess Tuning

Interesting details.
Some years ago, I bought an Austin Marina big valve head in here (Germany) and it has the carst in number 12 H 4736.
After serious porting and an advanced valve job (close to Peters information in his book How to Power Tune...), it is a perfect match to my 12:1 cr engine.

Seems there have been different stages of valve layouts according to export markets.

R.S. Ralph Siebenhaar

Peter - FRM

I have on the bench at the moment a head with both 12H2709 and 12H2595 as well as AF2H
all in raised casting
These are known as "O" series heads down here and they came on series two Austin 1800's which also had straight cut corods
The head has an 18 cast onto the r/h rear and an O on the l/h rear upper faces
They have the larger valves and very well shaped inlet ports
They are the best head out here to get to modify

just sayin ---------- Willy
William Revit

Hi Willy
the 2709/2595, 2709 and 2595 are the best for race heads. The only problems we have are these are the most prone for cracking and the larger inlet valves seem to have a tendency to recess in the head, hence using them for big valve race heads.

Peter
Peter Burgess Tuning

Yep
I've had a few cracked ones
Down either side of the centre headstud boss into the no.2&3 plugholes is the usual spot and also on the top of the head out from the valve guides.
Cheers Willy
William Revit

This thread was discussed between 01/03/2012 and 22/03/2012

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