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MG Midget and Sprite Technical - Cylinder head question

I'm pretty keen to have my cylinder head converted to unleaded BUT it's already been upgraded to run bigger inlet and outlet valves. Is it possible to do the U/L conversion on a big valve head or do I have to start again with a standard head and have the U/l conversion and big valve conversion done together?
graeme jackson

Hi graeme,

As far as I know, you only need to get the exhaust seats replaced with hardened versions - not the valves or guides. Any decent auto engineering company should be able to do it for you, but if you have anything else done as well, or are concerned they don't screw up your existing modifications, I'd recommend P Burgess.

Lawrence Slater

Yeah, peter burguss is the man...

Ultimatly its the individual machinist shop that will make that decision for you

It really comes down to the shops tools and there experiance, someone with just a pocket knife and a rock may not be able to do this , some one like peter burgusss can

But its a toss up in your case, theres not alot of meat between the valve to begin with.... Id explore the idea of hardened seats on both in and ex just to. Add some stability to the set up, i guess it depends on how big an over size you have
Prop and the Blackhole Midget

Guess it depends on how big your valves are, how big the insert is and how much would be left after cutting the seat to match the valve.
Have you checked what Vizard has to say? Give me a shout if you need to review a copy.

M McAndrew

short answer, yes. How much bigger valves? Is the head modified at all in any other way?

Cheapest and easiest would be to grab a later MG metro head, bigger valves and unleaded capacity from the get go.
Rob Armstrong

Cheapest and easiest way would be not to bother and just drive.

Cast iron is rather hard and can cope with a lot of miles before valveseat wear becomes a problem.

So if they are fine now just drive it and fix it when it becomes a problem
Onno K

normally I'd agree with what Onno's put but as rthe engine is out of the car and you have the time it would be a good time to get such things done

I'm (almost) sure I've read a post by Peter Burgess on here how he deals with unleading the bigger heads
Nigel Atkins

Onno has it - why screw up a head that will likely last your lifetime, given the use most of these cars get now? And it is possible that if it has OS valves now, you cannot fit inserts; by most accounts you cannot fit inserts to both seats, even if they are at stock size. If the inlets are big enough, there won't be room for even an exhaust insert.

FR Millmore

if it's only going to be a show car or lightly or rarely/not often used then yes totally agree

Graeme did say he was pretty keen though and I'm sure Peter would say if it was a bit iffy to do

I take the point that if there's no other work that needs doing to the head then for the sake of only unleaded petrol that the head could be fitted and worry about the issue if/when the head next needs work

sometimes though it's a reassurance issue with the owner and if that's the case now's the time
Nigel Atkins

I've got a P burgess head, unleaded, with large valves. 1300GT size, whatever they are.

As some here say, maybe not neccessary, but mines unleaded anyway.
Lawrence Slater

If all owners content to do work that would merely outlast their ownership there would be no midgets left.

That's the problem nowadays, no-one wants to do any more than the bare minimum with no thought for the future.

You kids get off my lawn!


No I won't!!
Hell I am building a new engine for the midget (I hope it will outlast me a long time), restoring a 32 MG D type and keeping a BGT for my wife in good shape.

This has nothing to do with not wanting to do the work.
But why on earth would you not use a perfectly servicable item that might even last you over 30000 miles as is.

I do not have a limit less budget so I want to spend my money wisely.
Certainly not a bad thing in this day and age.
Onno K

unfortunatly one of the best ways to preserve the cars is to assemble them to a good cosmetic order then not to use them at all or very little indeed that way it doesn't matter about the mechanical stuff so much - like they do in museums

now, if it's his lawn and he doen't want you on it you are going to have to move along :)
Nigel Atkins

I aim to do the least amount of work possible, and rebuilding a cylinder head again in 30,000 miles sounds to me like twice as much work as doing it properly the first time around.

That said, I appreciate that my opinion is somewhat atypical, and that most people are doing this on a budget. I *suppose*, if you *had* to, cleaning up a cylinder head and refitting it would be an adequate temporary fix, because you could at least fit the hardened seats later. But if the head is going to a machine shop it will only cost a little extra to get hardened seats fitted.

Okay...let me get everynes ire up in a tizzy

Ive been tempted on more then one occasion to purchase a good used valve and seat grinder...from like the 50s and 60s, these show up on ebay all the time...for less then $300 these where fairly common in gas stations that did mechanical work, back in the 50s thur the 70s before they became convinance seems like im always getting valves and seats $300 it would pay for its self in 6 valves recondition at the machine shop

Good idea or bad, it sure would save time...because ive never gotten a head done in less then 2 weeks

Anyway, sorry to hijack the thread

Prop and the Blackhole Midget

Sorry... 6 valves should be 16 valves
Prop and the Blackhole Midget

When you cut metal off, it is gone, Every unnecessary "must do" which isn't, is a net reduction in the life of a part or a car. If you can get 20 or 50,000 mi out of the head as is, that is that much "extra" lifetime. I do not overbore more than needed to clean up - if you really need the extra .020 for class racing, OK (maybe, still arguable), otherwise, live with what you have (and remove 20lbs of lard from the driver). I do not cut brake discs or drums except in very rare instances.

I have talked a lot of customers out of doing work that would have made money for me - 10 years and 6000 miles layer they still have virgin heads or blocks or cranks, ready for the first rework some day. I have been known to fit slightly OS valves to a head to keep from putting inserts in, and the inserts can always be fitted later, if the car and owner last that long. Also, there are damned few drivers who will actually ever use the 3hp that OS valves might give you, but very many heads that crack from having them put in.

And I feel the same about "restorations" - far too many perfectly drivable cars have much lifetime and all the history removed by dubious resto work, and a substantial number never get finished and are left as forlorn project parts piles on the owner's death. Wait until the part NEEDS rework, as distinct from the ego/bragging rights, etc.

FR Millmore

Onno is right, leave things as they are until it needs doing. That way you maximise the overall life of the component.
Try applying that principle of fixing it early to tyres; you would go and get a new ones a month after replacing a set on the basis that the ones on the car will need replacing in 2 years anyway.
Guy W

I agree about the point of not restoring a car to death, because I like the weathered "patina" look, if you can call it that. Others might call it the knackered look, I like that too :). -- But it must be a personal choice in the end. After all, a full restoration today, will be an old one in another 50 years time.

So is it 30000 miles, 50000 miles?

Either way, I think that's the first time I've seen an estimate of how long the seats of an unleaded head will last using unleaded fuel. Is that 50000 miles on top of the 50000 or 70000 miles it may already have done?

You have me wondering now.

If it's only 30000 miles, then since you can get 100000 miles out of an A series engine with ease, I would rather bite the bullet early, and do the unleaded deed. Much rather that, than have to pull the head off and do without the car for 2 weeks, only 30000 miles after a new build.

I suppose at 50000 miles it becomes marginal though, esp as some people might take 10 years to do 50000 miles.

And this isn't an academic question for me either. My 'spare' engine has an unleaded 1300GT head, that has done well in excess of 130000 miles. When I built the engine currently in my Sprite, I sent a standard Sprite 1275 head off to P burgess, and got back fast road unleaded with the same size valves as in a 1300GT head.

Now I'm going to rebuild the spare again, and figured the 1300GT head exhaust valve seats must be toast, for all the unleaded that's already gone over them. But maybe not then? The engine was used for a very long time when you could still get leaded, and for a while after that I used additives. Then for at least 50000 miles I used unleaded before pulling the engine.

Is it really possible that the head could be used as is with perhaps new valves guides and a grind? I haven't pulled the valves yet, so I will and take a look.

What's the most obvious sign of unleaded valve seat damage? Just recession?
Lawrence Slater

Sorry, correction. But I hope you figured this anyway. :)

Either way, I think that's the first time I've seen an estimate of how long the seats of an "LEADED" head will last, using unleaded fuel. Is that 50000 miles on top of the 50000 or 70000 miles it may already have done?
Lawrence Slater

Wow! some pretty polarised opinions here. Looks like I'll be stripping the head down in the next week or so - need to check the bores anyway, the engine hasn't moved in anger for over ten years - so I'll measure the valves then and have a word with some local engineers if I can find a decent one (any suggestions Mike? ). Obviously, if the work is possible then cost becomes an issue although given the amount I've thrown at the car so far a bit more probably won't seem too bad.

The later MG metro head sounds like an interesting choice - something else for me to consider.
graeme jackson

I got to disagree in theory

As lawernce says... Its a personal choice on what you feel comfortable with, and what is your purpose for the midget

lawrance, He loves the patina of a weathered look,,Onno loves the feel of what the car was as it came from the factory, Arie wants a the closet thing there is to an F1 race car thats still a midget and yet others just Want to drive the little car, for me its an art canvas for all my creative mechanical thoughts ideas and creations... Something to set my imagination free to roam about

We all make decisions based on greed and fear, when i had the crank shaft main straped, it was about both, it feed my ned for vanity as i know few others had this, and it feed my need to know the engine would be extra safe...irrealivant as to what the real possability of the crankcase imploding in on its self

Id say the reason why most people do hardened seats is ...its a cheap insurance for less then $30 a valve for 4, why not, eso when its going to cost $700 minume to have a head completly rebuilt...its good insurance

Why 214 stainless steel OS rimflow racing valves ???

if you have a big personality, you have to have big valves or you will appear to be normal or even avg if you have just run of the mill stock valves, granted when your at the pub with your friends you could lie and say you have them, but thats just not the way a larger then life personality blow hart lives

If life was only about economy and durability... We would all live in mobil homes and eat nothing but peanut butter and jam sandwitches for lunch and wear only zip up ankle boots brown

So if you want to know why someone is doing something il rational, like convert there radio concel box into a 10 gauge box to read things like vac and EGT... You have to look at the person and ask...or does only the minume and never buys a new part, retail price... You have to ask.. who are they, what is motivating there decision for hardened seat, is it greed or is it fear

Im just glad my favorite sin is vanity, because im pretty sure id hate wearing brown zip up ankle boots with with a black members only jacket


Prop and the Blackhole Midget

We used to figure that a light regrind at 50-60,000 would save major seat burning later - in the 70-100 range. If you replaced the stock & cheap CI guides at the 50/60 regrind intervals, the head and valves would go past 200,000 easily.

That was with leaded, but there does not seem to be much difference with unleaded fuel. Of course, the sample sizes and driving conditions have been greatly reduced. Proper unleaded seats and Stellite faced valves ought to last forever; trouble is, they are often not correct and inserts fall out or valves burn anyway because the guides wore out, or the clearances were not maintained. For either arrangement, correct installation and maintenance is critical.

Seat recession is the only real problem, but if clearances are not attended to, severe burning resulting in scrapping the head was the usual result - but I've seen this on inserted heads too. Severe seat recession seems to be an idiosyncratic thing, having to do with other factors of use and setup which I've never really figured out. Continuous full throttle operation (very rare), overheating (common), and crappy air filters (especially common on boy racer aftermarket crap) seem to be the major issues.

I've done hundreds or thousands of valve jobs and seen only a few cases of severe recession, and I've never put inserts in except to save a well worn head - and that wear was generally the result of poor prior regrinds, usually piloted off worn guides.

My rule of thumb became one valve regrind between engine OH, with mileages depending of maintenance; that might be 30/60 for poor maintenance, or 75/150 for very well maintained units. At the high end of this you start to get to doing two regrinds between OH, but that is rare, especially on BMC engines which ate camshafts, or TR ones that eat bearings.

FR Millmore

I've got 29.5mm exhaust valves and 35.7 inlet valves with inserts in the exhaust seats. No problems there.

And I didn't expererience valve recession on any of my vehicles until now. My '72 volvo B20 is rapidly losing it's exhaust seats. And I do mean rapidly, I have to adjust them every month orso!
Alex G Matla

Graeme, depends on how local you want. A mate had a modern head skimmed in Livi. I'll get the name of the workshop for you. Peter (Pedro!) at GEM in Falkirk is and old timer in a younger workforce and seems to know his stuff. They do a lot on Ford race engines and up to truck motors. He was very happy to show me around the workshop which was very well kept (always a good sign).
I used Engine Services in Rosewell for the inserts on the 1500 head but wasn't completely happy they didn't follow instructions to blend the insert in to the throat which left a step I had to finish. Workshop is a bit of a tip but again they are happy to show you around and were busy so someone likes them :0)

M McAndrew sounds good, BUT ???

The fly in your soup is the Head gasket ....when it fails, many of us just pull the head and take the lump to the machine shop and have the machinist tell us what needs to be done, and its always the same. As any other business ... Would you like some OJ with your ceral...its ONLY .99 extra,

Would you want the valves and seats cleaned up, its not leaking NOW, but it is a high milage engine, you know hardened seats are ONLY $30 extr per valve..ect ect

The thing is, most of us are not machinist or engineers, we know the basics ... Resurface the head, decoke, magna flux ect ect but i doulbt many know what you lined out or why.

It a decision process we all make based on our experiances and our greed/fear mecanism wether its for cars, refigerators blue jeans or big screen TVs... Its hard to fault someone for going beyound what is needed... Besides even if we do over machine something to death, its not like there is. a shortage of parts... Last time i looked on ebay a year ago for midget parts there was like 8000 parts for sale....breaking midgets for parts has gone from a hobby to full fledged contact sport

So i blame head gasket failures for the over building of heads and blicks... And it seems HGF is a common topic


Prop and the Blackhole Midget

No HG failures on my engines. Ever.

In the 1950/60s, we thought flathead Fords were everywhere (yes) and would always be (Nope)

In the 1970s. we had the same attitude about 55 Chevys and MGA, same deal. XK150 going for scrap because nobody would pay $500 for one.

1980s, it was Spridgets and Bs, now you get to search ebay and pay for crap, when you used to be able to pick good stuff up out of the trash piles. Good driver XKEs or 3.8 MKII were $2000 easy to find, Jag engines that needed anything were scrapped.

1990s, how many Datsun 210 or Toyota Corollas you want? A Midget that needs a gearbox? Haul it outta here.

2005, I could buy all the 90-94 Mazda 323/Protege I could eat for $4-800, excellent drivers off Ebay, junkyards full of them. 2009 they were gone off Ebay, check CL, a dozen any day within 250 miles for 800-1200. And the scrap thing took all of them out of any junkyard near me. Now, I find a few in a month on CL within my 250mi radius, either junk for 2000, or "collector" for 5-8000, and ALL the junkyards say "crushed all of those, sorry".

The American attitude of there's plenty of everything and always will be is stupid and obnoxious and WRONG! That we spread this cancer to the rest of a diminishing world is criminal.

FR Millmore

Wow. All this from a question about unleading a head or not.

Got any other controversial questions graeme? :)
Lawrence Slater

A controversial question?
I have been traumatised by watching Jim'll Fix It as a youngster. How much money can I now extract from his estate by way of compensation??

Coat on and gone!

Oh dear.

Well, I suppose that depends on how much you saw, when you watched Jim "fix it" ./.
Lawrence Slater

Graeme, another workshop I've heard some good reports about but its a bit further out...
Cameron Gilmour Engine Services
Unit C5 Errol Aerodrome Inds Estate
The Grange, Errol

M McAndrew

If it goes like this it ain't bad.

F Pollock

Looks like Oulton when the heater tap at the back of the head (being used as a by pass) decided it was not wanting to play any more now using a billet outlet from DSN and works great. Yeah Yeah I know its not an MG but most of the running gear is. Cameron


Cameron, where you been hiding!
Didn't know you were on here... The free reference above may be called in as discount on some engine work in the future..... ;0)
M McAndrew

Like the man said "nothing in life is free" come and see me any time and I will sort you out. I only come on here when a mate of mine lets me know if I get a mention, you know, nosey. very busy with work but always happy to advise.

This thread was discussed between 30/10/2012 and 09/11/2012

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