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MG MGA - Core Plug fit.

I am restoring a 57 A and started the engine for the first time [1800 5 main ] It fired up almost imediately and showed 60 psi @ 1500 rpm, so while I looked around for any oil/water leaks when it got up to temperature there was an almighty bang and rush of coolant as the rear core plug blew out, drowning the distributor and stopping the motor. Can anyone tell me the best method of installing this type of plug so it has maximum grip in the block.I have a 9 psi cap and coolant recovery bottle which is vented. I also have an original Smiths vacuum guage fitted and noticed at idle the indicator viabrates rapidly between 15 to 18 in's, however, bring up the revs and it steadies, Someone suggested valve guides, what do you think? Otherwise it runs sweet, Regards, Ron.
rj odonell

RJ,

I had a plug that leaked so I decided to replace them all.

First I was very thurough in cleaning the area where the plug goes - down to bear metal. Next I mixed up some JB Weld and put a small bead around the hole. I installed the plug itself by placing it in the hole, rotating it a bit to ensure the JB Weld was in contact all the way around and then dimpled the plug with a hammer.

None of them have leaked since, and I've boiled the coolant a couple of time with a 7lb cap.

Good luck!
John
John

Hi Ron. here is what I do: Clean the circumference of the frost plug recess with a small rotary wire wheel. Then take automotive silicone sealant, and run a thick, even bead on the metal where the frost plug will seat. Push the frost plug in by hand until it bottoms on the block casting. Then hammer on the "bulge" on the frost plug until it is thoroughly deformed inward. The deformity should be about and inch or so in diameter, and should be visibly concave. It takes a fair bit of hammer pressure and multiple hammer blows to distort the frost plug. I have never had a blown out frost plug, or a frost plug leak using this method of installation. Cheers! Glenn
Glenn

Hi RJ, when you have fitted the core plug as mentioned, carefully centre punch a ring of dots around the block casting about halfway across the flat surface around the coreplug hole, don't hit the punch to hard! This helps the core to seat firmly, the race boys drill and tap the block to fit a strip across the plug to help hold it in. I'm a bit concerned about the bang? Pinking/detonation can pop out a core plug as it is a shockwave that goes through the cast iron and literally shake's the core plug out. Is your timing/mixture/fuel quality correct?

Terry
Terry Drinkwater

Thanks for the info guys,the PO had rebuilt the motor and lightly/slightly depressed the centre. Terry the bang was the plug hitting the inner fender. There were a few different ideas from others ie belting the centre or using an old socket to knock the circumference in. I guess its better to blow a plug at home in your shed than on a cold wet night on a lonely road with the only light in the distance being that of Bates Motel. Regards, Ron.
rj odonell

A concave disk of metal has the largest outside diameter when it is flat. Under no circumstances use a centre punch to dimple the plug or concave it inwards. Clean the groove and select a core plug that just fits the aperture. Put a little Stag jointing in the base of the opening and fit the plug convave out. Then using a short piece bar which is almost as large as the opening insert it and tap the end with a hammer until the plug is FLAT.
Iain MacKintosh

This thread was discussed between 06/05/2005 and 10/05/2005

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