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Freeze Plugs

To: mgs@Autox.Team.Net
Subject: Freeze Plugs
Date: Thu, 14 Oct 2004 12:08:56 EDT
In a message dated 10/14/04 5:14:57 AM, Larry Hoy writes:

> The MGB freeze plug is tapped into place then dimpled with something like a
> ball pein hammer.  Clean the bore in the block first.  After it has been
> installed you could swab the edges with something like JB Weld.  That will
> make the plug permanent.
I normally wouldn't disagree with anything Larry says, but in this case, I
would make a couple suggestions based on recent experience replacing the
"freeze" plug on my MGA race car.
First, they really aren't "freeze" plugs, since they wouldn't pop if the
coolant froze; they're too high up in the block. They're machining plugs and
artifact of the way the engine is cast.
Second, you can blow a loose one by building up too much heat and pressure in
the cooling system -- I did mine by running a high-pressure radiator cap in a
car with an overheating problem that turned out to be caused by a leaking
Installation: Here's what my mechanical expert told me. Use a standard metal
(copper? Brass?) plug as original. Clean out the hole very carefully to make
sure the lip against which the plug will rest is absolutely clean. Coat the
edge of the plug with gasket cement. (I wouldn't recommend JB Weld, because if
you mess up the installation, you'll have a devil of a time removing the bad
plug to insert a new one.) Slide the plug into place. Using a small drift
1/4 inch head) start tapping at the edge, pounding in one place until the
metal starts to deform, then moving on around the circumference and gradually
moving in a spiral pattern towards the center of the plug. This will give you
good consistent deformation all the way around the plug. (Hitting it hard in
center with a peen requires really good coordination and risks deforming one
side more than the other.) By the time you're through the plug should be flat
to slightly concave. (In the "right tool department," if you've got air tools,
you could use a small air hammer to save the effort required by 15-30 minutes
of tapping to get the plug set.)
This worked for me and I'm no mechanic. The plug has thus far survived three
hours of racing time at 4000-6500 rpm and seems just fine.
Gary Anderson
MGA 1600

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