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MG TD TF 1500 - Frost Plug oreintation

The question is:

Should it be an "innie" or an "outie"?

In a high pressure vessel or a wine bottle punt, I can understand the need to present the pressure to the inward-pointing crown of the plug. But is that needed on a low-pressure application like a T?

I checked frost plugs on a few imported cars to see how the factory does it, and got both!

So what is it - an "innie" or an "outie"? Is there truly a scientific answer, or is it pure conjecture?

Should I keep a score-card on this one?

Gord Clark
Rockburn, Qué.

Gordon A. Clark

Hi Gord

It's an innie.

The plug is actually slightly smaller than the hole. It is concave so you can put pressure to the center(a nice whack with a ball peen hammer works well) and push the plug up into the edge of the plug hole.

Not sure how you could install it as an outie without it coming out.
Bruce Cunha

The nearly flat plugs go with the convex side OUT. When installed you hit the center with a drift; this flattens the plug and thereby expands the diameter to make a tight fit. If you overdo it and reverse the curve in the plug, the diameter again gets smaller, resulting in a loose plug which then is prone to self-disassembly. Cup-type plugs go with the concave side out, and the tension to seal comes from the sides of the cup.
FR Millmore

I'm with Fletcher.

Dave Braun

Think we are saying the same thing, but my terminology may be incorrect.
Bruce Cunha

Now I'm confused!

The plug is curved outwards when installed into the freeze plug opening. When it is tapped into place, 1/2" - 3/4" flat punch is the best. You tap the center and then go around the outside edges till the plug is flat, any further and you risk the chance of having the plug pop out. Yes, you can use a ball pein hammer but the punch gives you more control.
Ron Boisvert

You aren't confused, Bruce is! Bruce, when I get confused, I just remember that a conCAVE is something you can get into to hide, and if it's raining and you can't get in you are VEXED!
FR Millmore

I let somebody else do this on the TF this year...can't tell you "how" they did it...but I can tell you a few things.
1: What happens when it comes out at 65 MPH. (so long new pistons 3&4 and valves)
2: I was also told plugs ordered from Moss were "wrong size". (The large brass one behind the exhaust manifold).
3: The ones in there now came from NAPA and have held for aprx. 400 miles.
My appoligies to MOSS upfront if what I was "told" was wrong.... I am only repeating what the shop that did the work told me....they are no longer in business!
Cheers & Best Regards,
David 55 TF1500 #7427
David Sheward

Many thanks everybody for your input.

I think I am now sufficiently informed.

Gord Clark
Rockburn, Qué.
Gordon A. Clark

The large central one behind the exhaust manifold I had a problem with. I ordered plugs from 2 suppliers, inc Moss if I remember rightly, but both were still loose in the hole after almost flattening them. I wonder if the hole had increased in size slightly over the years, due to wear. In the end I turned down a oversize plug so it was a nice tight fit. None of the plugs I bought were brass, but steel.

Henry, they're metric. Next time go to your neighborhood Volvo dealer. I may have the part number. I seem to recall that they're 48 mm and that Bob Grunau carries them.
Bud Krueger

Henry and others
I purchased my last set of core plugs/ freeze plugs from Moss also. Some of them were the correct size, some were not. I ended up going to one of the local supply housed (NAPA) they had pull out parts drawers, where you could find and locate your own parts/ bolts/ cotter pins etc. They had both metric and US sizes in plated steel and brass. I purchased the next size bigger than the Moss supplied plugs. Took them home and dry fit them in the engine. They need to be a snug fit when initially inserted. If they are very loose at first, they will never tighten up. I was told that you should use a sealer (similar to contact cement) when installing steel core plugs by a noted club engine rebuilder. I did this and have not had a leak. Also it should be noted that you should use a blunt punch and do not drive them in more than flat. Hope this helps John

PS to Gordon Clark my answer is a Flattie?
John C. Hambleton III

Cannot understand why some so called mg specialists sell you the wrong part. Next time I shall source some metric ones, instead of spending a hour turning an oversize one down. On all occasions I used a gasket cement to help sealing, and hit the plug dead centre with a flat punch.

This thread was discussed between 21/08/2005 and 24/08/2005

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