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MG MGB Technical - freize plug installation

I am ready to to install new freize plugs on a 18V. the plugs are from moss and I would like to know if anyone can tell me the proper way and if I am to use any kind of sealer on them. I put one in to make sure they would fit and I find that they go on very loose.
RP Padilla

I can't remember if they are the cup type or the dome type. If they are the cup type, they should not be loose. That is, you should have to drive them in.

If they are the dome type, they will be loose until you put the ball end of a ball peen hammer on the center, and smack the hammer head with another hammer. This will expand them and make them tight.

I usually do put a bit of sealer on either type, but the most important thing is that the seat in the block is clean.

My most recent rebuild was a GK, and I think it was the dome type.

Also, if you search the archives, I believe you will find that Peter Burgess adds a safety strap over them to prevent them from leaving unexpectedly.

C R Huff

Have a read at (yet again,) Peter Burgesse's books He makes mention I think, But is it not a trick to put them in the freezer, get them really cold, then drive them in. As they warm up you will never get a leak. Mike
J.M. Doust

I recently fitted new core plugs during a rebuild, there's lots of info about on the subject. I put the first couple in using the ball peen hammer method, that is, ball end on plug then hit that hammer with another hammer. It was very neat but I wasn't convinced that the localised depression caused by the ball had spread the plug as well as it could have, it was a fairly small hammer and may have been better with a larger one. The next one I set by using an ordinary hammer giving the plug several reasonable blows until the centre was slightly concave and it sounded set. I pulled the first couple and replaced them using the second method with a couple of new plugs. You need to make sure the seat is clean, I used a small circular wire brush about an inch in diameter in a drill, a small bit of silicone sealant around the seat and the jobs done. I read Peters piece about straps across the plugs, but drilling and tapping the block to secure them seemed a bit OTT for road use. Mine are leak free at present but time will tell, fingers crossed.

R.A Davis

My first comment is DO NOT hit the face of one hammer with another unless you want shards of hardened steel in you eye. Use a mallet or a domed piece of steel intead of the ball pein.
Second comment, DO use sealant.
Allan Reeling


Not hitting one hammer with another I can understand, but no sealant? why

R.A Davis


Not hitting one hammer with another I can understand, but no sealany? why

R.A Davis

If you hit the ball pein hard enough to smash it, then you will have picked up the pieces of the block first,or have a cheapo ball pein.
Where did the No Sealant come from ??
Geoff F
Geoff Farthing

I think dislexia rules KO!! As far as can see my thread reads; "DO use sealant"!!
Hammers, good ones at least, are surface hardened, and believe me, the edges do break off. They are just not designed for impacting something of equal hardness. I hope I never have to "told you so", your risk!!
Allan Reeling

The hammer head shattering isn't something that you're likely to encounter when installing a couple of freeze out plugs. The required energy isn't there. A clean block is imperative and a bit of sealant, around the perimeter of the plugs, is good insurance. I installed mine this way, 20 years ago, and they never came out or leaked, nor did the hammer heads shatter. RAY
rjm RAY


I do suffer from mild dyslexia well spotted, fortunately it doesn't stop me enjoying these cars

R.A Davis

Long time since I did mine. No sealant and all i can remember is thinking, that will never stay in there, and as for keeping the water in....
I neednt have worried about it, the only one that fails is the one you cant reach. I.m sure they just fit loosely and only fix after spreading.
Stan Best

Sorry Bob, but i had to read my thread several times just to convince myself I had written what I thought I had written, ..............does anything stop us enjoying our old MG's?? Can't think of anytrhing at pres, OR in the last 40 years.
Allan Reeling

This thread was discussed between 20/05/2011 and 21/05/2011

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