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MG Midget and Sprite Technical - 1275 Cyl Head woes

Hi, new owner here. I've been advised to seek your expert advice!

I doubt I've driven 200 miles since purchasing my 1973 RWA 1275 midget last August. As I bought it so I could get to grips with the mechanics no one should be surprised it died with loss of compression on no2 pot. I say died but to be fair it did drive reasonably well on 3 cylinders but was a tad noisy under load!!

So, cylinder head removed [see image] I've got a hole in no2 pot exhaust valve. Excuse my ignorance but why has that happened? Would the seller have had any idea it was about to occur? Is there any way to know the current standard of the head, leaded/unleaded? Is it likely have been rebuilt already, or is the guesstimated 125000 miles possible on the original engine/head? Is there anything else that can be gleened from the condition of the head and valve faces?

Sadly the car has no history as the previous owner passed away and is unlikely to respond to a s

K Drew

Looks like pre ignition to me (pinking)

All you need to do now is take the head to someone who does that kind of work, get new seats fitted (might as well get unleaded) new valves where required and refit if the pistons have survived

Then set the engine up correctly.

If you don;t know who to take the head to simply ask.
Robert (Bob) Midget Turbo

Can't realy tell as the pic isn't that clear on my phone.
But usualy this kind of exhaust wear occurs because of a to lean mixture burning up the valves.

Your best bet now is take the head to a machine shop and have everything cleaned checked and fixed.
As replacing valves, guides and seats seems like the next job and they can't be done with out specialist tools.

You can also de decide to get your head to Peter Burgess or an other good grinder and have it flowed and modded.
Since a big part of the work should be done anyway a part of the costs have to be made why not go slightly further
Onno K

To keep costs right down could you not just buy a new valve, clean the head and go from there. The cost of new seats is almost the same as fitting a replacement headisn't it?

Dave Price

exhaust valves on 2 and 3 should be similar to 1 & 4 and not all sooty. Also the face between 2&3 shows some signs of breaking down between the pots (note how the rings made by the head gasket are much less defined between 2&3). It's possible you have been getting some cross contamination leading to preignition in pot 2.
It's also possible to do 125k without a rebuild but it's going to need one now!
New valves, guides, unleaded seats a little skim to ensure the face is flat. Check the block is flat also!
Or take the easy way out and send it to Peter Burgess for rebuild...

Would the PO know it was about to expire? Probably not unless he regularly checked and recorded changes in compression at a service.

Good luck


M McAndrew

Hi Kenny-
Perfectly normal extreme exhaust valve wear. Once the valve starts to leak, hot gases act like a cutting torch, accelerating the disappearance of bits of valve, all exacerbated by the valve no longer cooling as it is not contacting the seat in that area. This whole process is greatly aggravated and increased if valve clearances are not attended to. This process normally takes thousands of miles after it would have shown as low compression on that cylinder. It could be one thousand or less high speed miles, or 20 thousand puttering about.

A failure of this extent is a clear indication of poor maintenance and service, at least in the past few thousand miles. You rarely get a case like this with documentation, but I have a Rover 2000TC head that had low comp in one hole for about a year of daily driving c 50 miles/day, plus a 600 mile high speed trip to me. The valve looks just like that; unfortunately it did the same to the head.

#3 is also not firing properly, and I expect you will see an earlier stage of the valve failure there. The #3 poor combustion might also be a result of low compression due to head gasket leakage between cylinders, as indicated by the dark colour at the sealing face between #2 & #3.

Cyls #1&4 will show you the beginning stages of valve failure, as tracks across the seats. A good head machinist can tell you if the valves and seats have ever been reground.

It is possible that nothing was ever done to the engine, but more likely that at least the head was done in the 50-75 thousand range. In any case, it is very likely that the engine is plain worn out, unless it was totally and correctly rebuilt well into its lifetime. Cam & followers, and crank bearings, and bore wear should be checked before you go any further on the head. You can get an idea by dropping the pan to check rod and center main bearings, and can get a look at the cam for extreme wear, but my guess that you will be far ahead to just pull the engine. Very false economy to do the head without at least knowing what the rest is like; a new head will just let you beat everything else to (expensive) death.

FR Millmore

I'd check the condition of the bores and pistons to make sure bits of valve haven't damaged them. If all looks well it'll be a trip to Alex Carr's for them to inspect the head etc.

If you need a hand or want me to take a look then let me know.

J White

Thanks for the replies and the offer of help! The car is in North Yorks Jon so not as local as us!

The range of advice seems to be change a valve to replace the engine. I expect to do something in between, the head rebuild I don't suppose will break the bank and the good oil pressure and smoke free engine can do a few more miles. I do take the point however and don't see much of an advantage to getting the head gas flowed etc. So standard unleaded rebuild i think.

Good info regarding the cause, I had noticed the lack of distinction between the middle two bores and wondered if there had been some sharing of resources!
K Drew


A word of caution. It is easy to see what the outcome of a problem is and less easy to see the cause. 1275 A series are prone to burning out the centre ex valves. The cause is quite often oil coming up from the bottom end and causing overheating from poor combustion associated with lower cr and oil. It can also be a natural seat recession process.

The first thing I do when I inspect a head is to rub my fingers around the combustion chambers and onto the head face where the carbon deposits are, if the soot is soft and oil stains your thumb you have excessive oil in the head area. The source has to be checked.

The picture quality is not brill but the head looks gungy to me.

P Burgess

Kenny why not show your other picture of the burnt valve so Peter and the others can see the problem better?

Here you go. I was initially pleased to see the damage because it meant I had diagnosed correctly.

K Drew

Hi Kenny

Still looks like overheating caused by oil contamination. Remember valves do not just burn out of their own volition.

You need to strip the head to see if there is any evidence of seat recession.

The head does look very carboned up and does look like it has a tell-tale sheen of oil in the carbon.

Easier to say when it is sat in front of you and you can poke about :)

P Burgess

Thanks Peter.

I'm taking it to the garage on Saturday so will have a bit more info post that visit. I left it in Yorkshire last night, wish I'd brought it home now! Still probably best the garage see it as is and not after I've poked and prodded it!
K Drew

oh we're here are we, hello

no dispespect to anyone just a note, a garage is like a GP, Peter is a specialist

also taking the head still leaves behind the engine, by which I mean the head might show the results of the fault whereas the engine and rest might be needed to find the specific cause
Nigel Atkins

Hi Nigel

I think some people may think I bite :)

They also do not seem to understand I do not charge for looking and that I have a few heads under my belt.

P Burgess

"I have a few heads under my belt"

Is one of them Nigel's! :)

Peter if I were nearer, you would have been my first choice as I have heard a lot of your expertise. I am still hoping to do most of the work myself, so machining aside I will do the refurb. As for the engine it will no doubt need a dose of looking at and I will also carry out as much of that work as I can. This is one of my toys and I intend to enjoy all aspects of owning it.

Appreciate everyones comments. Thankyou.
K Drew

if you can master the dark art of the Archives here there's loads and loads of info and opinion

also to speed up answers and save confusion of what model and year if you wanted to you could easily add your 'Vehicle profile' to your posts - click on any one else's 'View vehicle profile' scroll to the bottom and follow the simple instructions

and on Customise you can change your presentation of name and area

so you've been cured of the biting, good I hope it lasts

I think Bill and I might have mentioned you to KD before

have you other strings to your bow???

(and on Customise you can change your presentation of name and area)
Nigel Atkins

Message to Pete Burgess. Totally random...

You're not by any chance the same Pete Burgess who was Clem chair at Imperial College London some years back?

Long shot, but you never know...

C L Carter

Sorry not same one....I was at North East London Poly, Stratford for my sins :)
P Burgess

Peter - are you in Avon area now - I thought you were up north somewhere?
Dave Price

Oi, get off my thread and go to friendsreubloodynited! :)
K Drew

I cannot get it to let me change Avon to Derbyshire!!!!!

P Burgess

by the way - are you Kenny Drew who used to work in Asda because......................
Dave Price

sorry =]
C L Carter

"by the way - are you Kenny Drew who used to work in Asda because......................"

Dave, are you the bloke that used to come in and get over excited in the mens underwear section? Last I heard you were arrested in Matalan!

Never mind that though, what do you think to the cylinder head?
K Drew

No need to be irritated this is just the way it goes on this BBS.

Regarding your head.
Send the head to a shop and let them check it.
If you want a durable solution I'll bet valves, guides and seats should be done.
A clean won't do it any bad and have flatness checked.

To easly check the block set all the pistons half way down the bore.
Then pour an equal ammount of petrol or diesel in each bore.
Then time the time it takes for the bores to drain.
If any bore goes a lot faster than the others you have a ring sealing problem
Onno K

I'm happy with the banter O, no worries!

The head is going to my 'specialist' on Saturday. The tip about piston ring sealing is useful thanks.

BTW I loved the Netherlands when I lived on the border. I once asked a girl where are all the ugly Dutch girls, she replied they were all put on a boat to England as babies! Gotta love 'em!
K Drew

Oi, remove that photo of my filter, oh well perhaps not mine technically yet, but, could you perhaps semi-fade that photo and have it become fainter or clearer as a barometer of trouble the head/engine/car - I've got the cleaner and recharger out of the shed ready :)

can't you just overtype it instead of useing drop down menu, Kdrew's managed - it'll be another string to your bow
Nigel Atkins

Interesting, you keep your cleaner and recharger in your car?
K Drew

no they're by the computer and monitot poised for action should that photo fade away entirely

being very carefree with the cleaner and recharger I've only used 20% out of each bottle, they're taking up space I could use for other stuff

did I mention I have K&N special edition black mesh pancake filters now with vibrant red cotton to match red Mk3 Midgets - I'm having the car resprayed a brighter red to match the filters
Nigel Atkins

Yep love our girls!

Especialy mine!
Bussy planning wedding using wedding cars sevenoaks stuf in between work and midget stuff
Onno K

Alex G Matla

Onno - wedding you say??????

Kenny - I was not arrested just asked not to return for a few years!!!
Dave Price

Kenny - back to the head. I have just refitted mine. It looked pretty carboned up as well as pitted at the valves but I cleaned it all of using Bore Gel - gun cleaner - and elbow grease and lapped in the valves, tried a fluid leak check and they were OK.
My problem is a lack of funds or should I say wife and children!!!

Just dropped sump today to trace oil leak so do not know what else I might find but all going well.

To be honest I love tinkering with these cars and the BBS has lots of helpful chaps and chapessess here to point you where you might - I say again - might - need to go.
Dave Price

I know Netherlands is liberal but I didn't know they had legalised marrying sheep....
David Smith

Got me confused with Arie again....
Onno K

If anyone can tell me how to changte it to Derbyshire I would be most grateful. My address and everything shows Derbyshire so I am non-plussed and not a computer whizzkid :)

P Burgess

Aha done it but had to mess about and change user name too......We are about 4 miles away from the Oak tree in Morton which is claimed to be the centre of England....please note this is a physical tree and not (sadly) a hostelry :)

Is that OK Mr Atkins? A spare string to my bow :)

Peter Burgess Tuning

Just to hi-jack the thread.

Nigel was teasing me for my archery with a spare string.....
Military English Longbow archers kept a spare string for their bow as a string might only last a few shots, an archer might only loose 48 arrows in a battle and it was not unusual to use two strings and maybe even snap a bow. The spare string was often kept dry under the archers hat....hence keep it under your hat. The technique of drawing a bow mainly uses the back muscles....hence...get your back into it.

Absolutely nothing to do with cylinder heads or Asda or weddings :)

Peter Burgess Tuning

Wikibleedinpedia, friendsreubloodynited and Cylinder head advice. Everything in one place, priceless!
K Drew

I am creeping closer to Lincs/N Yorks though :)
Archery is at Barlborough which is still Derbyshire even though Yorkshire tried to steal it in the 70s.

Peter Burgess Tuning

well done Peter Burgess Tuning, you keep your fingers :)
Nigel Atkins

Over in general, on another thread, someone mentioned a law by the name of Godwin. Now I've made an observation, that perhaps dicates a new law for bbs. At least the Spridget bbs at any rate.

How you noticed that if a thread goes on long enough, someone brings underwear into it? There've been a number of threads with this mentioned. Far more I think than subscribe to Godwins law.

What is it about Spridgets that can invoke mention of underwear? lol

Back to the head. You mentioned earlier that it was/is a smoke free engine. That seems to contrast with the evidence of the oily carbon deposits.

Beofre you take the head to a garage for them to charge you, why not drop all the valves out and have a gander at the guides and stems? Then post a pic or three, for more helpful and otherwise commentry. :)
Lawrence Slater

Now then Lawrence, I used to study psychology so I am within my learned rights to ask," How long have you had this morbid interest in underwear Mr Slater?"

To 'go the whole hog' can we have a recipe on this thread? Sort of pan fried headcasting on a bed of lightly toasted coil springs, sprinkled with carbon flakes and drizzled with sump oil.

Peter Burgess Tuning

It's a shame but I didn't bring the head home from Yorkshire with me after I removed it. I didn't run my finger round the head and check that what looks like oil isn't just a black glaze of somesort. A bit hopeful that I admit!

I have also changed part of the exhaust and therefore done some running with my eyes, nose and ears near the back end and she wasn't smoking as far as I remember. On previous runs I hadn't seen any smoking either.

So the heads at the specialist Saturday and I'll have a good chat about it then, the cylinder bores looked and felt good and the piston tops didn't look overly discoloured or oily.

I mentioned the underwear but it was Dave's fault!
K Drew

Hah Hah. Hmmm. Is it morbid to have an interest in underwear?

I confess to being interested in such garments, when revealed on the person of a semi-naked female. But not so interested, in a fully or semi-clothed male wandering around Asda or Matalan though. :).

And surely Peter, if you were to 'go the whole hog', you'd have to spit roast the head, rather than pan fry it. :) Speaking as someone who once read a cookery book that is, and haven't poisoned myself yet lol.
Lawrence Slater

My Fault!!! It was all a mis-understanding
Dave Price

Well Dave, if it was all a misunderstanding, why exactly were you arrested in Matalan, or asked not to return for a few years then? :)
Lawrence Slater

I suppose we've done the cylinder head until the next update at the weekend so go on Dave confess all then we can all move on and maybe take up bows and arrows! Peter, did you never fancy being a cowboy?
K Drew

ohhhh, now you've upset him, not so good in your situation :)

wrong bows, wrong country
Nigel Atkins

Funnily enough I have a Winchester air rifle and sit with it helping John Wayne in True Grit....FILL YOUR HANDS........!

Failing that the clue is...English Longbows not American Short bows....mind you any bow is long when you are my height :)

Peter Burgess Tuning

Ok, back to the cylinder head!

Inspection revealed it has been removed before there are marks suggesting an emery cloth clean of the mating face. The water ports have not suffered any corrosion and look clean. Rubbed my finger round the valves and surprisingly no oil so am more confident of the pistons and rings. There has been some cross contamination between 2&3 and the head will need a bit of a skim. The valves are old and the tops are slightly deformed, so I need to check the tappets. They would have been difficult to adjust. There is slight corrosion at some of the cylinder edges but not a problem after a skim.

A reasonable health check I thought.

Nigel the air filter will be refitted!
K Drew

>>Nigel the air filter will be refitted!<< uhhhhm, for now :evillaugh:
Nigel Atkins

Sorry for the delay in replying - had to defend myself again from some nasty allegations, this time in M & S. I said its for the wife but..... well their arguement was - "If its for the wife why are you wearing it?"
Anyhow all sorted for Xmas - My head is all back together and tappets done - just sorting the slight oil leak underneath. I say slight - the bottom of the car is covered from engine bay to rear axle - no rust this winter!!
Dave Price

did you use the cork sump seals by any chance

I never had a leak until replacing those U seals, I trimmed to obviously incorrect size as the sump just wouldn't offer up unless I did
Nigel Atkins

Dave, I fear you may have a problem. What seems perfectly natural to Nigel and yourself is a mystery to us manly MG enthusiast types.

I won't be collecting my Cylinder Head until the end of January due to bloody festivities and a well deserved holiday. (Nigel. youve got a month to find it on Google maps before I return). On refit I'll be attempting to do the same as you by dropping the sump and having a rummage!!

Did you refit tappets or replace? Have checked mine for wear and they dont look as bad as the valve stem tops, so perhaps newer than the valves. It's easy to keep replacing bits isn't it?
K Drew

Nigel - I kept the old rubber ones as the cork ones look - dodgy - I will probably use the rubber ones as they look OK. The leak seems to be from the front face.
The rad is slowly coming out to remove the plate etc.

Dave Price

Kenny - reused all the parts - money is tight!!! The valves needed lapping but that was a doddle to be honest and I tried the liqued leak test and all was well. If anyone here is into shooting Bore Gel works a dream on removing carbon etc.
Dave Price


Cork sump seals usually don't need trimming. If they extend about 10mm out of the groove each end they end up with a nice amount of compression and fit nicely. Trimming them off more-or-less flush always makes them leak.

I once had a leak cause by tank cleaning the sump. It scoured out the sealer between the sump and the spotwelded bit that forms the groove. Oil wasn't getting past the cork seal, it was the gap where the sealer disappeared was the problem.
Paul Walbran

Dave, what's bore gel, and where do you get it?

No comment on your M&S activities. What anyone chooses to do, in the privacy of a public shop, is their own business. LOL. btw. Does the wife like previously worn items then? ;)
Lawrence Slater

Lawrence -
I got some from School - I run the cadets there and I thought I would give it a go. Took the old carbon off the rocker area real easy and some blue paint came to light.
As long as I wash them afterwards SWMBO doesn't mind!!!
Dave Price

As a matter of professional interest Kenny will you go leadfree and what is your head going to cost for what work you are having done?
Peter Burgess Tuning

Although I can find no reference in the BMC workshop manual, Haynes states that the cork seals should be 1/16" above the sump flange and should be trimmed if higher than this.

I have always trimmed cork seals to this measurement and have not had leaks.

I did, however, have the same problem as Paul, having had a sump acid dipped, it leaked on the inside of the seal/flange.
Dave O'Neill2

Do you recommend I use the cork or the rubber seal then?
Dave Price

I like the cork seal more I leave it 5mm above the flange gasket and have no problems with it.

Onno K

leak at front sump seal

Paul, Dave,
thanks for your info, on my second attempt I did leave the front cork seal sticking up as I followed the photo in the Haynes as the text was ambiguous - my 1982 copy, page 44 says 'making sure that they bed well down in the housings and if necessary trim off any surplus protruding above the sump flange the sump flange gasket level (photo)'

I was at a mateís as he has a lift and when we offered up the sump with gaskets we couldnít get it to near enough to get the short bolts to the thread on the engine between us and as we had no other suitable longer bolts we decided the front cork seal must need a bit nipping off

Later as I was having a lot of work done by a (supposed) model expert garage I asked them to replace the sump gaskets for a third time thinking a professional marque development expert company would do a better job of it than I was capable of Ė they werenít

The back sump seal was a black plastic(?) type which I considered also using on the front as well next time

the irony is that I only had to drop the non-leaking sump because of a stupid mistake I made and I only yesterday ordered a 1974 copy of the not very helpful Haynes to see if itís better than the 1982 version I have

Iíve got my spies out in N Yorks but if youíve only really done 200 miles in the car then itíll not be easy to spot

just for clarity Peterís only done a RR set up for me but as he was a third of the cost and three times as good as my previous visit to a renown A-series RR tuning expert and previously Iíve been to an average RR tuner and a very good one with my present and previous Spridgets I know when the results are good on the road

Iíll be back to Peterís next year perhaps with my new filter :)
Nigel Atkins

This thread was discussed between 11/12/2011 and 21/12/2011

MG Midget and Sprite Technical index

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