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MG Midget and Sprite Technical - Bent Valve?

I have taken the cylinder head off my car and have taken all the valves out so I can clean up the seats however the exhaust valve in number one was very difficult to get out and now will not slide back in at all is it possible the valve is bent slightly? I have tried the exhaust valve from number 2 cylinder and this slides in just fine to that has ruled out the valve guide being faulty?

I have cleaned up the valves as best I can with a wire brush however the exhaust valve still looks rather rough? Is this just the standard coating on the valve?

As the the exhaust will not go back in what are my options? Buy a second hand standard exhaust valve and lap it in or go the whole hog and have the cylinder head converted to run on unleaded? Due to financial restrictions I am looking at spending as little as possible due to my printing business being very slow at the minute.

C Carter

And exhaust valve.

C Carter

Pic of the seat and stem would be useful. :)
Lawrence Slater

I thought I took a pic but cant find it on my phone I will take one at lunch time and post for you.
C Carter

This is uncanny. I did this job 2 weeks ago. *Different C Carter here*

I can't see how the valve would get bent - unless possibly it got very hot and the sideways force of the cam bent it. Doubtfull though.

I would have guessed valve guide if you hadn't mentioned you checked that.

It looks like the valves still have carbon all over them - I'd soak them in vinegar or coca cola overnight (something slightly acidic) and the carbon will all flake off... you might find it will go back in.

Alternatively - if you are on the cheap (like me) then your suggestion will be fine... it won't take much to lap in a different valve. I would also reccomend lightly lapping in all your valves - I did this and the increase in power is amazing! Wish i'd done a compression test before and after to compare.

C L Carter

Hi Christian,

How effective is the coke and or vinegar trick for removing carbon? Can it be enhanced?
Lawrence Slater

I am as confused about the valve not fitting as you are? These are original valves non hardened what should they look like all cleaned up? I was worried about wire brushing off too much? I will put them in some vinegar on my lunch and see how it goes.
C Carter

Hi Lawrence I will try the vinigar trick and let you know tomorrow how effective it is?
C Carter

I wanted to try it last time only I didn't have anything like that in the garage I was working in. So I used petrol instead - and soaked it overnight. I've heard coca cola is the best though - the fizz really attacks the carbon. Pete Burges is the man to ask - he must know.

See photo of head after night soaked in petrol though... carbon began to lift off - was a dream to clean after that.

I have a few photos of the valves - but they won't show you much. Will post in a second.

Chris, where does the valve get stuck - straight away, or nearer the head of the valve?

If near the head it could be carbon build up, if near the end then it could be that the cotters have created a slight burr on the valve stem - this would be easy to clean up.

C L Carter


C L Carter

valve again

this is covered in oil in case you think it looks odd

C L Carter

another valve pic

this is the carbon on the other side of the valve - it comes down the stem a bit so, this could be your problem if it goes in most of the way.

C L Carter

Thanks Christian I am going to soak over night, You might be on to something with a burr as it is right at the end it wont go in at all I will check the valve stem for any burrs.

I am going to soak my cylinder head tonight in either petrol or coca cola? And the valves in vinegar and hope fully I will find a burr on the stem. Did you simply wire brush your cylinder head after soaking?
C Carter

I used a brass brush - I wouldn't use a steel brush if I were you.

You can get some good brass pipe cleaners and tooth brush like brushes - invaluble when doing this...

I also used a nylon brush and a real toothbrush. I used a razor blade to clean remaining head gasket off the gasket face.

Then I used a light scotchbrite to clean everything up. But you can use the green side of a washing up scouring pad.


C L Carter

I have a brass brush on my dremel so was going to use that. Well I will post some pics before and after.
C Carter

Plenty of elbow grease later and this is what I got to after...

Was definitely worth spending an hour or so lapping the valve seats. They aren't perfect - but I now have a good sealing edge - I can't see the point in having hardened ones put in until mine become thoroughly buggered.

C L Carter

I completely agree do you have a pic of your valves themselves after they have been cleaned up?
C Carter

The one being held on the grinding sucker has been cleaned up - but only in petrol and a bit of scrubbing. I only bothered to remove the worst of it cos it all went together fine. Theres no point in going overboard - cos in 100 miles it will all be black again.
C L Carter

What is the face of that valve like? Did you do anything with that?
C Carter

I don't know a huge amount about these 'modern' valves, so I assumed the face doesn't matter that much. Perhaps Pete Burges would have something more to say if he's reading this?

I lightly cleaned the face of the valve on an oil stone - just enough to give it a flat smooth surface which my valve grinding sucker would adhere to

C L Carter

We tend to grit blast valve faces and underhead areas to remove the deposits. I havent found any chemicals which remove the hard deposits. Softer carbon flakes off after a good soak in a hot caustic solution or a cold soak in a strong acid. Leave stems well alone only clean up with something like 400 grit cloth in adjustable speed drill. You can chip off the deposits or scrape them off with a screwdriver, plenty of elbow grease though. You can even 'polish' the face with 60/80 grit paper. Valve face finish varies depending on manufacturer, some are machine finish and easy to clean up, others have the cast finish and are harder to clean. Most inlet valves seem to be en52 magnetic steel and most ex valves seem to be 21/4n stainless ( non magnetic), as stainless has low scuff resistance the stems are usually treated with a chrome plating, tuftriding or plasma nitriding.
I hope this info helps?
Peter Burgess Tuning

We must al be doing this in parrallel. I have cleaned up all my valves using my pillar drill and some light wet and dry for the valve face and rear valve head. works a treat...

I will post some pic's if this will help ?
John Barber

At first glance, that first photo of the valve held on the grinding stick looks like an enormous giant valve held in your other hand! No wonder it won't fit!

I think all the later 1500cc midgets had this giant intake valve - see pic below.. Shown laying alongside the exhaust valve to the right of pic...

John Barber

On a serious note - pic below shows my head recently skimmed and new hardened inserts plus all valves cleaned up using pillar drill and wet n dry...

John Barber

You think your pistons can count? ;)
Lawrence Slater

Very nice, but you have got valve #9 in the wrong place. And upside down!

Damn - do I have to take it out and swap it ?
Or do think the pistons will notice ?
John Barber

Love the giant valves. Must get some!!
Mind you I was amazed when I took the head off the midget engine. The last engine I rebuilt was a lotus twincam and the valves on that seem enormous in comparison.
T Dafforn

Well photos cannot lie - can they?
In that first photo Christian is clearly holding the valve between his thumb and forefinger of his right hand, which to me puts the head of the valve at around 85mm. Rather larger than my My Metro 35mm ones!

I soaked the head in coca cola overnight and gave it a quick brush with a brass brush and this is what I ended up with. Along with the valve before it was cleaned.

C Carter

Pretty good! You guys are putting me to shame!

I'm glad the cola works - but was it sainsbury's basics cola - or Pepsi max!
C L Carter

It was ASDA Smart price cola at 18p a bottle! 5 bottles used to cover it up and to be honest I was pleased with the result.
C Carter

This thread was discussed between 30/03/2012 and 02/04/2012

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