Cylinder head 12G940

[Steve Linfoot]

Can any one tell which 12G940 head I should be looking for to fit my 1098cc engine, I've seen some on e bay,some older ones that look like they have the heater control valve ports,newer ones that don't or at least they don't seem to be drilled through, can these indeed be drilled.
Later ones also have the thermostat cover plate at different orientation to my original head so maybe a problem connecting the radiator top hose.
Also I'm not sure if any have the bypass hose connection.
If anyone can advise me it would be most apretiated.
Steve

[bmcecosse]

Avoid the large inlet valve version - save it for a 1275! Yes the heater port can be easily drilled, the threads are there ok. The stat cover is at a different angle (to small bore heads) on them all - just use a curved top hose - mine was cut from a bottom hose. I assume you know about the need to take care of the exhaust valves.

[Steve Linfoot]

Thanks for the reply,
I know the larger exhaust valves can foul the block, but what is the biggest exhaust and inlet valve combination I can use without block mods.
Do you know if these heads use the bypass hose?.
And what's a A plus head are these better ?
Steve

[bmcecosse]

The exhaust valves on a 940 head WILL hit the block on a small bore engine - you must make space for them - detailed regularly - search for it! Better without the bypass - either block the pump - or get a 'no-bypass' pump. There is no useful difference between the heads as far as A/A+ is concerned.... Later 'unleaded' heads will be more difficult to sink the exhaust valves - earlier leaded heads may well have exhaust valves already suitably sunk, so you won't need to do anything!
Remember you need 1275 gasket - and sintered rocker gear, or spend some time re-aligning the pressed steel rocker gear from your 1098 engine of course.

[ajsreeve]

Hi Everyone,

This is my first post here! Although I have spent many hours reading through posts. Just need some advice before I make any rash decisions to buy. I am looking to upgrade to a 12G940 head on my 1098. I have found this one on Ebay that looks to be a good deal. http://www.ebay.co.uk/itm/CLASSIC-MINI- ... 1767418700

There is a huge difference in price between refurbished and non refurbed heads it seems. This one is clearly not refurbished. I don't really want to fork out £250+ for a refurbed head if it will cost me less to fit a stock head. Has anyone got an idea of costs involved with getting this old head to fit and the process involved? From what i'm reading it sounds like ill have to pocket the block, fit new springs and valves and port the head... Still trying to get my head around this! Any help appreciated. Hopefully the link works.

Thanks, Alex

[panky]

Hi and welcome aboard That head will take a lot of work to sort it out, at least one of the valve seats is badly burnt so I suspect a few new seats and guides will be needed along with valves, springs and rocker gear.
This one looks a better bet and you could put in a cheeky offer

http://www.ebay.co.uk/itm/MINI-CLASSIC- ... 1723275617

[bmcecosse]

That head is ludicrously expensive - with no valves/springs/collets or cotters.....It will cost a fortune to make it serviceable. Avoid avoid. Buy a complete 940 head with all the valves etc included. You should NOT 'pocket the block' - far better to sink the exhaust valves in the head - IF necessary. And really no need to 'port' the head either - although a little bit of easing down the exhaust throats where they turn the corner at the guide won't do any harm..
Note that second head above is the large valve version - great for a 1275, not wise on a 1098. It's also stupidly expensive - even for a large valve head...

[panky]

You do indeed need to proceed with caution and don't jump on the first head you find, but they are going up in price unfortunately
I did the conversion and with an 1 1/2" carb and decent exhaust it works very well. I had a different approach to the valve problem, instead of sinking the valves I skimmed the face of the valve to give the desired clearance of at least .320" between closed valve face and head face (the A+ exhaust valves have loads of meat on them). Here's how I did it.

http://www.mmoc.org.uk/viewtopic.php?f= ... 7&start=20

[bmcecosse]

I wouldn't take a lot off the exhaust valves - they need all the 'heat capacity' they can get.... But if just a few thou needed I guess no harm. I sold a '940' head last week for £40 - with a gasket and rockers etc, as part of a deal with a Marina 1275 engine (with MG cam) I was selling......also at I suspect a 'bargain' price ! But the market in Scotland is not so great for these things - so when the opportunity presents....

[ajsreeve]

Thanks for the tips bmc and panky - some great pictures on your thread!

This head didn't show up on my initial search as it didn't have 12G940 in the title - but the pictures/description show it is. It seems to have all springs, valves etc and have been refurbished. It is still a leaded head however... Would this be alright to use with fuel additives or is it best to make / buy an unleaded conversion?

http://www.ebay.co.uk/itm/mini-1275-GT- ... 4aee557f80

BMC due to my inexperience and lack of time spent looking at cylinder heads I can't spot the difference between the small / large valve type. Could you explain how I do this so I know what to look for?

[bmcecosse]

That appears to be a small valve head -it's the size of the inlet valves.... And you don't want twin valve springs -but you could always remove the inner springs... It's still a lot more than I would pay....but there don't seem to be any 'reasonable' heads on ebay at the moment. Whatever head - you don't need to waste money on 'unleaded' additive.... Just run with 15 thou valve gaps and check/reset every 3000 miles.

[ajsreeve]

So assuming I get the 12G940 head. Overbore the block +0.020 to give 1115cc. Fit std Imp pistons to get 1215cc. Fit a 270 cam... etc... This is all probably going to cost more than buying a 1275 engine that runs. (seen one on ebay recently £500) I would probably be better off just buying the std 1275, cleaning and rebuilding that. As for the gearbox, prop shaft, rear axle... Stella (my morris) is a standard set up for 948cc engine at the moment which is what the original engine was (although the gearbox is new, it's still a 4 speed no syncromesh.
What i'd like to know is if I increase the size of the 1098 to say 1215 would I have to change to 5 speed gearbox, uprated shaft and new diff? I've read somewhere in the forum that this is a must if using a 1275 engine. Just trying to gauge the pros and cons of highly tuned 1098 or bolt on mods to a 1275. Any thoughts or advice would be appreciated. Just trying to get all of this out of my head now, before I go about researching and buying parts for the build.

Thanks all!

[amgrave]

If you can let us know what you are trying to achieve by the upgrades we would be in a better position to help

[ajsreeve]

Yes that would certainly help!

I am not looking for a racer. My aim is fast road car. She will be my everyday car, so must be fun to drive but also build for some more demanding longer journeys. Not particularly TOO worried about economy... I have in my armoury Vizard's bible which is very helpful. Although he does seem to focus on racing spec engines most of the time... every time I read further I can feel my wallet getting lighter haha

[philthehill]

My advice for what it is worth is to fit the 1275cc engine and follow through with other modifications later - the 1275cc can be either Marina/Ital or Midget/Sprite and go from there.
So long as you are not too hard on the throttle the gearbox can cope but fitting the later 1275cc Midget/Sprite box would be better. As regards the standard diff the same applies. The weak spot on a Minors transmission is the half-shaft but again so long as you are not heavy footed they will cope with the extra power and can be up rated later.
Whilst I agree Vizard is more to the top end of the performance engine spectrum in his book Tuning the 'A' Series there are lots of basic things contained in his book that can be done to increase the power without spending a huge amount of money. A companion book of his 'Tuning The Mini' gives a more basic view and gives more of a do it yourself overview and there is a companion to that in the form of 'More Mini Tuning'. Both are available on 'e' bay from time to time.
You can tune the 1098cc to give extra power but you are limited in the rev unless you have a MG/Sprite engine with a engine number prefix of 10cc which has 2" mains so is more reliable and can be revved.
You cannot beat the extra cc and torque of the 1275cc engine.
As regards fitting a Ford 5 speed gearbox to me the costs are all out of proportion to the benefits gained, better to change the diff ratio to either 3.7 or 3.9 to give a better cruising speed and the 1275cc engine will cope well with those diff ratios.
What ever you do - do it well and do not be afraid to ask.
Phil

[bmcecosse]

'ajsreeve' - you certainly have some very mixed up thinking there.... Fitting 'Imp' pistons (can you find them?) doesn't increase capacity - unless you bore to suit. All a waste of time on the 1098 engine - fitting a 940 head is about the limit worth doing on a 1098 with it's 6000 rpm limit - even the large mains version.... A 1275 engine is a whole step up the cost ladder -so you need to decide how much power you want and how deep your pockets are.

[philthehill]

The 10cc engine is a totally different beast from the other 1098cc 'A' Series engines and is well able to be tuned and made to rev freely above 6000rpm; and was and still is used in historic sports car racing.

See the attached:-

http://www.spridgetguru.com/TA0012_file ... 8_1098.pdf

[bmcecosse]

It's still uber long stroke - would need careful strengthening (centre main) and lightening/balancing - with S type rods.... I don't see the point of all that expense unless it is to squeeze into a particular competition class. For a road engine - stick to 6000.....

[amgrave]

Philthehill. After reading your attached PDF does page 10 say a 3.7 diff from a 1.5 Riley will not fit a Minor axle or am I reading it wrong?

[bmcecosse]

It does fit....