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MG Midget and Sprite Technical - 12G940 head - seat inserts

Does anyone know for sure if the original heads were supplied with valve seat inserts when new, or (as I suspect) the seats were just machined straight into the casting?
TIA.
David Smith

I cant say for 100% fact ... but im 97% sure that both intake and exhaust the seats are machined in the the head ... but the exhaust could have had hardened seats added later on by there owner at a local machine shop...fairly common

The (1318) smog head didnt come with seat inserts and the ( 940 ) is a duplicate of the (1318,) just without the smog ports


Prop

Prop and the Blackhole Midget

No inserts AFAIK
Dave O'Neill 2

Hi David

OE non A plus no inserts except when repaired by Goldseal, other machine shops or nowadays leadfree compatible inserts. A plus heads in Metros from 198? (someone help me here?) shallow exhaust inserts to be leadfree.

Peter
Peter Burgess Tuning

I've got an unmodded low mileage std head lying here that says no inserts.

As the rest has said.

But I am always amazed how long they last with unleaded fuel.
Onno K

thanks all for the confirmation.
David Smith

Yup me too. I've just pulled the valves from my 1300GT head. I never got around to having it unleaded, and I've done over 120K miles on it. I used to use super unleaded on it before I pulled the engine. All it needs is a valve lapping. Amazing. I've often been told that the lead from previous fillings would protect it, now I know there must be some truth in that.
Lawrence Slater

IIRC it also depends on how you drive it as the valve seat recession didn't really become a problem unless you revved it regularly above about 4.5k RPM IIRC.

CNG cars have this problem potentially as it has no lubricating effect whereas even unleaded has a small benefit. CNG cars need even harder valve seats than unleaded cars to stand up to continuous use especially if you drive almost constantly running CNG.
David Billington

Lawerance,

Come on now, give credit where its do, those ""suprise"" lead balls in your gas tank paid off, and saved your valves

Hahaha

Prop
Prop and the Blackhole Midget

Lawrence, when you lap the valves you will remove the combustion product deposits which have enabled your engine to cope with leadfree conditions thus far. I am surprised if it doesnt show some ex valve seat recession even if it had run leaded all its life. Maybe you are a gentle driver with it?

Peter
Peter Burgess Tuning

Hi Peter. Ah well looks like I might have to get inserts then after all. I thought the lead somehow perculated down microscopically into seats rather just being on the surface.

I'll take a pic. But they don't look recessed to me. The valve faces sit nicely at the top of the seats. I've already had a go at the exhausts, and got a good seal after grinding them with fine paste.

I used to hammer the engine too. CooperS pistons 30+ and 1300gt head. Easily topped a ton, and I used belt down the A20 from south london to Rochester in it everyday for almost a year, overtaking everything that didn't want to drive at 90 plus. so it definitely had a good caning. Very typical of how I used to drive. :).

That was back prior to 1990/91. Since then it's done zero miles, as it's been sitting in my gargage as my spare awaiting a rebuild. It's replacement was the engine I fitted one of your heads to. Fast road unleaded, which now I'm older and more sensible, doesn't get quite the same caning. :-. Having said that, the bottom end is rattling now, hence the need to rebuild the spare. I was going to use your head, but seeing the good condition of my 1300GT head, I figured I'd re-use that as is -- cost free. Then put a new bottom end in the current engine and sell it as a complete going concern.

Now though, given what you say, I'll have a rethink I suppose.

Hey Prop. Good idea. Surprised you remembered my lead balls. lol.
Lawrence Slater

I can never forget your lead balls, that was such a classic topic....I just loveed the fact a PO actually bought into the idea....it gives you a smile that optimistic hope is still alive

Prop
Prop and the Blackhole Midget

Prop

There must be plenty of people falling for it, if they're still selling them after all these years.

There may even be some cars that have been 'treated' more than once, by successive owners. Tanks full of lead balls and no room for petrol!
Dave O'Neill 2

Here's one of my exhaust valves in situ. Doesn't look recessed to me. My understanding is that if the whole of the valve face, sits on the whole of the valve seat, then it's ok. If that makes sense that is.

But if I've ground all the lead off, I don't suppose that matters much now.

Speaking of lead balls then. If one were to hang a lump of lead in the tank, would that impart ANY lead to the petrol at all, and hence to the seats? Judging by the comments below then, I guess not.

Lawrence Slater

And the answer is? , --- no. It won't work with Elemantal lead. You need Tetra-Ethyl lead (TEL).

So my lead balls in a cage can stay where they are as a decoration in my garage.
Lawrence Slater

Looks like a hardened seat lawerance....but you know how I am with stuff like these

Id think grinding up into.a fine powder oil base paint chips would be more advantageous in the gas tank then lead based fishing weight balls

Prop
Prop and the Blackhole Midget

No insert there.

I would take it to a machine shop and at least have them machine 3 angle valve seats in there.
That is an easy gain for low valve lift flow.
Though the seat area is less with 3 angle seats and that would mean faster wear with out inserts......
Onno K

With the 1275 heads the ex valve throat is a little wide to get a good seat profile, fit inserts with smaller than standard ID and hey presto, nice seat profile, albeit with a slight venturi into the throat due to the smaller ID blending into OE ID.

Peter
Peter Burgess Tuning

Peter. How does my 1300GT head compare performance wise to one of your fast road 1275 heads?

If it is hardened Prop, it was done before I got it. I pulled from anAustin 1300GT in a breakers back in the early 1980's if I remember correctly. And certainly doesn't look like it has inserts to me either.
Lawrence Slater

The Fast road head has same valve sizes but modded throughout so makes a fair amount more esp with inc in CR. Sorry can't be more specific.

Peter
Peter Burgess Tuning

Cheers Peter. Just confirming which one to keep.

Since I have to strip both engines anyway, I might as well build my keeper with your fast road head, and sell the other engine with the 1300GT head -- leaded or unleaded.
Lawrence Slater

A Plus heads from 89 were unleaded...
j hall

Thanks, but my question was about original Spridget heads which are by definition pre-1975.
David Smith

This thread was discussed between 17/11/2014 and 23/11/2014

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