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MG MGA - Core plut replacement woes

Help! I need some suggestions. While I was trying to replace the weeping middle core plug on my 15GD engine something bad happened. A piece of the block broke off. About a 1" portion of the inner "shelf" where the core plug sits broke off and dropped into the block. I've managed to get the broken piece back with a flex magnet. But, what now?

I'm wondering about trying to grind off the rest of the "shelf" and then fitting a rubber expansion plug. The only other thing I can think of is replacing the block.

Has this happened to anyone else?

Thanks for any tips.

Dave
David Ahrendt

Hi Dave. Most MG engines use the "flat style" core plug, which is a disc of steel that is slightly domed. This style of plug likely relies on an unbroken "shelf" to seal properly. However, there is a newer style of core plug, that is shaped like a shallow cup. I suspect that this style of core plug relies on the cup "sides" to seal. Therefore this newer style of metal plug might work, where the older style probably no longer would. Check a good auto parts store to see if they carry the size of cup shaped metal core plug you require. Another possibility would be to obtain a rubber plug that expands once in position. Usually these plugs expand by turning a nut, which compressed the plug , forcing it to expand diametrically. Again perhaps a well stocked auto parts store would have something off the shelf that that would handle the broken block issue without any real difficulty. Best of luck, and Merry Christmas, Glenn
Glenn

Dave. For the cup type core plug to seal, the block has to be perfectly round in the hole the plug fits into. This means removing the engine, stripping it down and fitting the plug. Major effort.

There are two thicknesses of rubber core plugs. a thinner one and a thicker one. My local Checker auto supply had both in stock when I needed one. The thinner type plug worked well and allowed the engine to be run for several thousands of miles before it was pulled for rebuilding. As I remember it, the thinner plug has an all metal cap with a hex nut cast into the cap. The thicker plug has a washer and hex nut on the top. The thinner plug barely protrudes from the block while the thicker one protrudes about 3/8". Hope this helps.

Les
Les Bengtson

Hi Les. The cup type seal I am thinking of is a very slight interference fit in the block. A bit of gasket sealer around the circumference would likely take care of any potential seepage. I have used this metal cup type core plug when a core plug rusted through on an old Ford Tempo of mine. Installation involved putting a bit of silicone sealer around the core plug, and also around the hole in the block. A few smart taps from a hammer, and the plug was well seated. I then waited a few hours for the silicone seal to harden, then filled the cooling system. Not one drop of leakage! My cup seal didnt require any great preparation or effort to install. Cheers! GLenn. PS, Merry Christmas Les, and Everyone
Glenn

Glenn. But, you are forgetting that the cup type seal is made to fit into a hole that does not have a lip that stops it from moving, thus, not allowing it to seat properly. At least that was my experience on the one American engine I have rebuilt. The hole on the I-H Scout engine was of the same diameter into the water passage. All of the BMC engines I have rebuilt, A, B and C series, have had a two diameter hole--the basic hole and a larger diameter hole for the core plug to fit into.

Thus, the cup type plugs do not go in sufficiently far to seal properly. (Theory only--I have not tried this myself after measuring diameters.) The thicker expandable (rubber) plug may work. The thinner expandable plug does work and will hold up for several thousands of miles.

A Merry Christmas to you and to all of our friends throughout the MG world.

Les
Les Bengtson

Thanks for the info guys.

I'll look into both the rubber expansion and cup type plugs. With a portion of the inner flange broken off there is not much depth available for a rubber plug to grip. The idea of trying to grind away the remains of the inner flange is not too appealing but it would allow a rubber plug to fit deeply into the outer hole.

The cup idea does seem easier but I can see how you can't drive one in completely. So I wonder how well it will hold up. How about buttering the back side around the circumference of the cup and the face of the remaining flange with J-B weld and then using a sealer on the sides?

Les:
I carry rubber type plugs in the spares kit for my TC but they're the relatively tall, maybe 1", of the flat washer and hex nut variety. I've never seen the "thin" variety. Do you have any idea of a name for these so I can try a Google search? Using expansion plugs only comes up with the thick species.

Thanks,
Dave
David Ahrendt

Hi Les. I just dug out the spare cup type core plug that I had for my old Ford Tempo. The cup is only one quarter inch deep, and I am pretty sure it would seal the MG block core hole without difficulty, if one of proper diameter could be found and installed. As usual however, there seems to be more than one way to skin a cat. I say, use whatever works best and is easiest to install. With the engine still in the car, a rubber plug is likely the easiest to install, and would also provide an effective seal. Merry Christmas everyone! Glenn
Glenn

On the race engines, we either epoxy the plugs in place or even drill and tap a small hole on each side of the hole and bolt astrap across it to keep the plug in place.

Try the cup type and see if it seals. If not, anything up to and including MIG welding the cup style into the block may be called for - just make sure you use antifreeze from now on, as you won't have the safety of a plug any more.
Bill Spohn


I finally found a reference to the thinner type expansion plug. They are called "Quick Seal - Copper" and are from Dorman. I now have a NAPA #BK6004028 so I'll check these out tomorrow assuming NAPA is open.

Here's another reference I found:
http://www.lbcnuts.com/mg/tidbits/tempfreezeplug/
David Ahrendt

David,
The copper Dorman plug is the one you want. It should serve as a permanant repair.
J.H. Hall

David. That is what I used and it worked well for more than a year. Make sure it it tightened fully, run the engine up, let it cool and see if it can be tightened up more.

As to "strapping" the core plugs and/or using a little JB Weld to help hold them in place. Both are good ideas depending on how much work you want to do and how competent you are with machine tools. Properly cleaned core plug recesses are the first thing to start with, regardless of type of plug. Get a rotating wire brush in there and clean everything throughly if at all possible. A thing layer of JB Weld along the outside edge of the recess (the 90 deg corner where the inner flange, which the plug seats against transitions to the wall coming outwards to form the recess for the plug). Spread the plug using a large drift and a heavy hammer. Add some more JB weld along the joint between the core plug and its recess (outside of core plug and within the "sidewalls" of the recess).

But, remember that the use of epoxy, or cross straps, do not guarantee that a plug cannot come out/leak. The plugs must be installed properly--sealing like they would if you were not using any secondary method of sealing. The secondary methods (epoxy/straps) are not a bad idea, but are not a replacement for proper installation technique.

Les
Les Bengtson

This thread was discussed between 24/12/2005 and 26/12/2005

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