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Midget and Sprite Technical
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Thread: So that's why it sounded lumpy.
Posted 12 October 2017 at 20:42:17 UK time
AdrianR, Bucks, UK

Cylinder head appears to have suffered a bit in the years while the car was parked up.

Opinions on whether this could be rescued by fitting new exhaust valve seats? It's a 12G940 casting with standard size valves but has had some light porting work done in the past so was probably a bit better than stock in its day.


Posted 12 October 2017 at 21:04:53 UK time
1 Paper, Missouri, USA

Id say a quick hit would sona world of good on the seats and valve faces would be a good idea being its all apart...the correct tools of course (valve grinder and seat facer) plus have the guilds re reamed to make sure there not sticking,along with some valve seals and your good to go, make sure the springs havent rusted thur or weakened

But yeah a little spring clean up and she looks good

The 12g940 head seems to get good reviews here on the board over the years on the smaller A series engine

Good luck with it


Posted 12 October 2017 at 23:48:34 UK time
William Revit, Tasmania

It's a bit hard to tell how grotty they are by pictures but it's surprising how well seats recover with a cut
Inserts would certainly fix it up properly OR go a size larger with the exh. valves and that will give you more material to work with getting the seat height up to spec
Looks like it needs a skim as well--the gasket has been weepy there in a few spots, specially round that centre brass plug ,it appears that it might have sunk a tiddle in that area
Anything is recoverable--go for it

Posted 12 October 2017 at 23:51:51 UK time
David Smith, Berkshire, United Kingdom

reckon CMES (Classic & Modern) in Bracknell can advise & sort that for you. They do all the race engines for the A35 Academy series and they're not expensive either.

Posted 13 October 2017 at 06:44:20 UK time
Peter Burgess Tuning, Near the centre of England

When 1275 heads show poor seats like yours, plus overheat signs twixt 2/3 cyl ex valves we find a fair few cracked in the middle ex port on the rocker face side of the port, it usually shows as almost black between the pushrod holes over middle ex port. We usually use some emery cloth on a split rod to flap out the roof of the port to ensure crack free before working any further on the head.

Posted 13 October 2017 at 10:08:24 UK time
P Bentley, Surrey, United Kingdom

Picking up from'Yoda' Peter B. . . i had similar issues with a crack as PB describes and following the advice of the company i used i had the head Vacuum Resin Injected. Apparently this system is used a lot on cast parts particularly in motorsport as it fills the microscopic cavities in cast items. Leading to a reduction in failiures.
I used a firm in Slough, and since re fitting, post modding, no issues at all.
Being the sceptical type, i was re-assured when i dropped it off, and collected it to see a number of motorsport company boxes being packed with wheels, components etc. . . .might be worth investigating.

Posted 13 October 2017 at 10:59:12 UK time
James Paul, North Somerset, United Kingdom

Could be worse!


Posted 13 October 2017 at 11:26:29 UK time
AdrianR, Bucks, UK

@Peter - this head (let's call it #2 for chronological reasons) is cracked as you describe, there is a distinct lip in the roof of the exhaust port. This happened many years ago (1990s), and was repaired with some sort of pour in sealant. The repair was sufficiently succesful that I'd forgotten that episode until your comment.

So, what else have I got? This is head #1, an AEG163 casting which has also been ported at some stage. Unfortunately it's cracked between the valves and also around the thread at the base of the #4 rocker stud.


Posted 13 October 2017 at 11:33:15 UK time
AdrianR, Bucks, UK

Head #3, a standard 12G940, no cracks but some sort of erosion around #3 exhaust port. I'm not sure if I ever ran this one, but looks like it might have had new seats at some stage. Also seems to have been built without rubber valve step seals.

And finally there is head #4, a another standard 12G940 that I have just bought on ebay - head only, no valves or springs but looks OK.

Must be some combination here that will run!


Posted 13 October 2017 at 12:02:28 UK time
William Revit, Tasmania

P Bentley
In reference to the vac resin injecting
A mate here took his BigHealey block in and had it done as they are a bit prone to being on the porous side and wanting an oil leak free Healey decided to spend the bucks and get it done
They let him in to watch it all happen
First the big cleanup bath that stripped it bare, then in the oven to dry it out
Then it went in the vac tank and he couldn't believe how many air bubbles came out of the casting, then out it came to dry

First pink engine I've seen

Posted 13 October 2017 at 12:31:38 UK time
William Revit, Tasmania

Peter B
With the crack in the exhaust port--
Would you say that happens to the heads with no coolant holes along that side more than heads with the coolant holes or is it more of a random thing-
I've never come accross it but then havn't done a real lot of A series work either

Posted 13 October 2017 at 19:53:44 UK time
Peter Burgess Tuning, Near the centre of England

Hi Willy, I cannot point my finger at any particular 1275 casting to be honest. I will try and keep a closer eye on variety/vs cracking.

Posted 13 October 2017 at 21:04:50 UK time
1 Paper, Missouri, USA

Id think on #4 they could add some welding to the errosion then machine it out or insert some new seats ...thsts probably the one id go with considering the other 3 are all cracked in some way then just use a larger exhaust valves and the best of the 4 heads from everything else

But thats me


Posted 14 October 2017 at 12:30:56 UK time
b higginson, Cheshire, United Kingdom

"I'd think on#4 they could add some welding"
It's cast iron Prop.

Posted 14 October 2017 at 13:27:32 UK time
David Billington, Wiltshire, United Kingdom

A mate had the crack in between the inlet and exhaust in his 12G940 head welded and it was very successful. An old very skilled Polish welder did the job and ground it back to near the correct profile and I recut the valve seats.

Posted 14 October 2017 at 16:54:25 UK time
Martin , Washington, USA

Cast iron can be welded but, as David says, it takes someone who knows how. There is a place near me that specializes in doing that. And I've had heads welded in the past with great success.

Posted 15 October 2017 at 13:14:00 UK time
AdrianR, Bucks, UK

The valves on head #3 cleaned up OK so currently thinking I'll lap them in and try that to get the car running again, and keep head #4 to build a better one for the future.

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