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MG MG Y Type - Fitting new core plugs to a Y - Top Tips wanted!

I have been putting off the replacement of the core plugs on the r.h. side of the block below the exhaust manifold: plugs of both sizes have been weeping for a couple of years and it's now getting unsightly in an engine compartment I am trying to keep presentable.

Before I get stuck in, does anyone who might have done this before have any Top Tips for me? I know the basic approach, having done the job on A-series engines in my youth, but any suggestions, dodges or warnings would be very welcome. In particular, are there any views on the use of epoxy to seal the edge of a new core plug in the block? Seems to me this might help stop the problem recurring.

Thanks for any contributions!
Tim Griggs

Modern ones all are the wrong size! Mine were replaced by an engineering company when the engine was out. They never sealed properly afterwards despite them using "proper XPAG"ones. I couldn't be bothered to take the engine out so have bunged epoxy putty round them - seems to have been satifactory but the area needs to be 110% dry before you do it. Drain the radiator AND the block,leave to stand for at least a day before you start, chisel off any loose paint then press small amounts inplace, allow to harden before the next layer. Unless your existing ones have "blown out" leave them in - always carry some in the glove box and some putty. Do not remove unless you have to!

You can paint the putty if you want.

Paul
Paul Barrow

If you do change them paint them inside and put them in with the paint wet it helps them seal.
John

Core Plugs.


When the engine is designed, there has to be sufficient space put inside the cylinder head and block casting for water to be able to circulate, to cool the engine. Some areas are very critical, and these are the four exhaust valve seats. The castings are not solid, they are hollow, and usually with an average thickness of the walls of about three quarters of a centimetre, ( a quarter of an inch.) Some areas are much thicker, depending upon the load they have to take. Of interest is the casting technique developed by Ford of America in the late 1950’s, where their ‘thinwall’ castings were only about a quarter of a centimetre, ( an eighth of an inch.) They also used spun-flow-cast-iron for their crankshafts. Morris used solid forged carbon-steel for their crankshafts, and grey cast iron for the main castings. American Fords were only designed to last a few years, and the cheaper they could be made the better.

As the castings of the head and block are hollow, something has to be placed in the moulding die to create the voids. The iron is heated up until it is a liquid and is ‘cast’ in specially baked sand die moulds. The ‘pattern’ for the casting is made of wood, and ‘pressed’ into the sand to give the outer shape, then the wooden pattern is removed. The insides, or voids are made by baked sand ‘cores’. There are two ‘cores’ in an ohv cylinder-head, one for the waterways, the other for the inlet and exhaust ports. The ports are easy to support as they join to the outside and inside of the head, but the waterways are more complex. You cannot ‘suspend’ a baked sand core in the air, it has to be located accurately, giving the correct casting wall thickness. If this is not done, the cylinder boring machines would break through into the water core when they were machined. So the void that is to be the engines water jacket, starts as a ‘negative’ of its internal shape, in sand. This sand ‘core’ is supported at various points by the outer sand of the casting die mould, so when the casting is done, there are holes through the walls into the water jacket. When the casting is cooled, and all the sand blasted out of the core, then these holes are machined round, with a slight lip, for ‘core-plugs’ to be fitted to seal up the hole. Now the water jacket is complete.

These core ‘plugs’ age round discs of metal, that are pressed out convex, then machined so the rim is truly round. They are then put into the machined hole of the casting wall, where they are a very close fit. Then they are hit firmly at their centre, spreading them. This causes them to grip the hole, and seal it, or ‘plug’ it, hence ‘core-plug’.

Now you know that core plugs have nothing to do with popping out when the water freezes inside the engine. This does occur, but only when the water freezes behind a particular core-plug. If the water froze between two cylinders, it would crack the cylinder wall, no matter how many core plugs are fitted. Most engines use one size of core plug. Others use three or four. Core plugs can also be fitted at the rear end of camshafts, to keep the oil from the rear camshaft bearing in the engine. The XPAG has one fitted inside the bell housing, on its rear cylinder block face.

Core plugs are made of about 16swg mild steel. Mild steel rusts a lot more quickly than cast iron does. So core plugs can get thinner each year, and eventually start to weep water. The rusty water run from the core plug will warn you they are about due to be changed. To remove them just hit them in the centre till they are concave and so become loose. Often the centre falls to bits first, and you can flick them out with a screwdriver. All are very easy to get at, except the one at the rear of the block just below the head. It can be easier to remove the gearbox cover and attack it from behind. Once out, the water jacket needs a good flushing out of old rust and sludge. The machined core-hole in the block or head needs cleaning up meticulously as the new core-plug will rely on ‘gripping’ the hole. Again, to fit them hit them in the centre with the ball-pein part of a ball-pein half-pound hammer. Do be selective where you flush out the block, as that rusty water will stain any driveway or road for months.

If the lip of the machined hole in the casting has corroded a little, then a little instant gasket is permissible, and it may be worth putting some Radweld in the water. If you use the correct ratio of good quality antifreeze, core-plugs have an infinite life. Remember, the engine makers would like to do away with core plugs as they are an additional complication. But no one has yet designed a suitable sky-hook to support the internal core of a casting.
Neil Cairns

Wow- thanks for the speed of the ideas so far: this must be one of the most helpful boards around! I forgot to mention that I run the coolant with a fairly high level of corrosion inhibitor to prevent silting problems in the radiator and thermostat: no sign of rust in the water after six years... so presumably the backs of the core plugs should be clean. I shall look at the plugs' edges and see if they can be resealed or whether they need to be replaced.
Tim Griggs

Tim

Bear in mind that to get a good swing on some of the core plugs you need to take the engine out!

Paul
Paul Barrow

Henry Ford insisted the the original series V-8 engines, 1932-1953, be cast with out core plugs. When rebuilding one of these monstrously heavy blocks, residual casting sand is often found inside.
Epoxys will displace water as they cure, but the glycol in antifreeze can act as a barrier to adhesion.
Scott Barrow

Guys, good info but no one has mentioned using brass core plugs,I find these last much longer. One could argue with a good coolant you do not need brass but mild steel will always corrode much quicker than cast iron. Definitely do not use stainless steel as this will create serious corrosion of the core seats. I am with Neil, make sure the seats are very clean, I use a scribe to make sure the corners are clean where the plugs seat and an immersion grade sealant for belt and braces. Cheers Richo YT3208
Richard Prior

Core plugs are neccessary as the sand-core internals of the casting have to be supported. It is all but impossible to cast a water cooled block without core plugs being required, either as cheap expanding steel plugs, or as screw-in type.

Neil.
Neil Cairns

The MG Octagon Car Club sell care ploug kits for the XPAG, for about £6 a set. They are on UK 01889 574666 or < harry@mgoctagoncarclub.com >

Neil.
Neil Cairns

This thread was discussed between 18/02/2004 and 25/02/2004

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