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MG MGB Technical - Cleaning Valves

I've got the cylinder head in pieces as it's off to be skimmed tomorrow. The back of the inlet valves are covered in a stick black substance which looks like it is burnt on. Any ideas how to get it off? There's also some in the ports but not much. Also, any ideas how to clean the valves generally?


Neil Lock


i have had this too and taped the shaft of the valves before i put hem into an electric drill. Using a sharp iron or knife, you can clean the valves this way.

After the deposits had been removed, i cleand the area with fine emerypaper.
If you follow this way, you shold take care not to damage the seat area of the valves and beware of the black dust!


It is oil that has run down the valve guides - clean them as Ralph says or, if the deposit is hard, mount the valves in a drill and use a sanding drum on a Dremel to clean the valves.

When refitting the valves use the improved MGC type of valve stem seal on the inlets.
Chris at Octarine Services

Soak the valves for several days in "oven cleaner"
(kitchen cleaning).

It'll help soften the crust; then chip off the rest with a sharpened wooden "popcicle" stick.
Daniel Wong

My method has been to use a coarse wire brush on them, rotating the valve as one area is cleaned. Whichever of these methods you use, wear safety glasses while cleaning the valves.

Les Bengtson

patio cleaner takes it off as well as for cleaning alloy wheels
Ste Brown


If you can get them, around here all of the mechanics in the BCC recommend using the FORD UMBRELLA valve stem seals.

James Huggins

Daniel Wong has the best solution. Soaking in oven cleaner is the slow but best way to get the baked on black crud off of your valves. Yes, it is the slow way, but the risk of damaging the surface of the valves is considerably lessened. Surface scratches become stress risers, and a broken valve in a running engine can be a pretty traumatic experience. While the head is at the shop to be skimmed, now is the time to install hardened seats for operation with lead free petrol.
Steve S.

all oven cleaner is is caustic soda which can be got from chemists
used to de-coked our bike exhausts with them yrs ago
also de-anodises coloured aluminium back to original plain colour
Ste Brown

Should have guessed it was baked-on oil; in fact, it looks just like the crud you get at the bootom of the oven (I knew it looked like something I'd seen before....!). I was thinking it was a result of the octane boosters I have been using, plus a mixture of unleaded and 4 star (which I cannot get around here any more). I think I'll scrape a bit then go for some oven cleaner to see if that works.

I had the old-style o-rings on the stems which clearly cannot work! I've got some of the 'improved' rubber boot type ones from Moss to go back on. The valve is a pretty good fit in the guide though so I'm not overly concerned.

No need for hardened seats, I've got them already - and bronze guides, and 43mm wasted stem inlets, etc, etc, etc. The head's in the shop to raise the CR a bit (10.5:1 before you ask...) to go with a new cam (Piper 285).

All I've got to do now is get the old one (Kent 717) out!

Neil Lock

This thread was discussed between 07/03/2007 and 08/03/2007

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.