Welch Plugs, Freeze Plugs - a Primer

Welch Plugs. Expansion Plugs, Freeze Plugs, Disc Expansion Plugs, Cup Expansion Plugs - even sometimes misspelled as "Welsh" plugs.

They came about as an answer for the need to cheaply and reliably seal the ends of bore holes, and do it without taking up a lot of room, or requiring exotic materials.

On the WD 45 for example, they can be found at:

1. The sand cast ports in the bottom of the head (famous for rusting out)
2. Back of block where the rearmost camshaft bearing sits
3. Transmission cover where the shift rails fit.

Welch plugs get their "Freeze Plug" nickname because they are used so often to seal the holes left behind that are needed to extract the sand from engine block castings. This usually is a problem where the water jacket around the cylinders is formed. And when someone makes the mistake of using no antifreeze - or too little of it - those plugs will pop right out with the first cold snap.

The Wd 45 engine doesn't use freeze plugs for the water jackets, because it uses "wet sleeves". There's no cylinder bore to get in the way of extracting the casting sand when the engine block is poured.

But its OK to call them "freeze plugs - they been carrying that nickname for about 100 years now - much as circular saws are called "Skil Saws".

The more important thing to remember is that the guy at the parts counter likely will not know what the heck you are talking about, so it may be a good idea to memorize ALL the possible name choices.

Welch Plugs are a truly American Invention. Not only that, but they are a Michigan invention, first made in Pontiac, and now Oxford. Fact is, the original company still produces them and are located about 1500 hundred feet from my favorite breakfast joint.

Here's the the facts, as told by the Great Grandson of the company that originally manufactured them:






There's a couple of excellent sources for plugs: The best of course is Hubbard Spring, which has the broadest range and greatest experience in properly installing them.
http://www.hubbardspring.com

A second, widely distributed product range is Dorman Products (they've been around since 1918) and their famous trays pf fasteners can be found in most quality, full-line hardware stores.
http://www.dormanproducts.com/c-238-concave-expansion-plugs.aspx

Whether you get expansion plugs from the tractor dealer or one of the sources above, do yourself a favor, go to the Hubbard Spring site and read the installation guides they provide.

There are as many wrong ways to install these plugs as there are so-called "Experts". The most important things to remember (and there are only three):

1. You are working on a not-new piece of machinery, so clean, and clean again. And then inspect the
bore. Make sure past leaks or damage caused by extracting the old plug haven't eroded or scored the
seating surface.

2. Use a sealant - and use the CORRECT sealant. Permatex #2 works well, and so does Permatex #1
(hardening) in most water environments. Materials like RTV - are NOT good - they actually will help
that plug to pop out. Just the slightest coating on the side wall of the bore where the shoulder of
the disc meets it will do.

3. Use the right driving tool. Hubbard Spring goes to great length to accurately describe the proper
tool for use in a manufacturing process. BUT - you are not a manufacturer. The best "tool" it turns
out is often the drive side of a socket that is slightly smaller that the diameter of the expansion
plug. Take your time to set the plug into the bore and make sure it is bottomed, set the "drive tool"
squarely to it, and rap it hard enough to cause that disc to compress to nearly flat. Don't bother
trying to use something much smaller and "tapping all around it" - you'll end up with a disc that
looks like it lost a war, and will just drop out of the hole.

Well, there you go - a bit of enduring American history and technology - and still relevant today.














Edited by CJohnS MI - 30 Aug 2010 at 10:28pm

Did Allis source from Hubbard or Dorman? or both? Anybody know?

As far as "popping" out to save engine block in the event of water in jacket, it's been my experience that they do pop out right after the block cracked! In fact, I always half joked that it was the block cracking that relieved the grip on the plug