The Stovebolt Site Forums The Shop Area Engine Shop 235 Engine Block Corrosion

It appears to me that there is rear top cooling jacket plug, see photo. This one is badly corroded but it appears that freeze plug is installed from the inside, not like the two on the side of the block and the one to the right of the block.
If installed from the inside can one be installed from the outside. I’ve cleaned the circumference of area and I can’t see a plug lip like the plugs installed on the side of block.

If you're talking about the one between the top two bell housing bolts, it's definitely installed from the outside. How would one install a core plug from the inside? If you look closer, you should see a step in the bore, unless it's been corroded away. I don't recall exactly, but I think that it's a cup style plug like the ones on the side of the block. Those don't need a step, but are just driven in so the edges of the cup are flush with the block surface.

The existing plug really looks like if it had been installed from the inside but I agree with you “how you or anybody install it from the inside.”? It makes sense to install it from the outside. Which is what I’ll do. The one there now is corroded through.
Thank you

It's shaped like a disc and there is shoulder in bore. Remove the old plug and you will most likely find some gunk you will need to clean out. Put the new disc in using something that is almost as round as the disc (I use a socket). You can put a little permitex in the bore before installing the new disc.

The replacement disc is convex and when you hit it in the center (don't bash it...just a medium smack) the circle will naturally get larger. As mentioned above, use some Permatex non-hardening sealer around the inner shoulder.

The disc type plug is a Welch plug. A little trivial history: The Welch plug is dome-shaped and inserted into the casting hole with the convex side facing outwards. When installed by striking the Welch plug with a hammer, the dome collapses slightly, expanding it laterally to seal the hole. This differs from other dish-shaped core plug designs, which form a seal when their tapered sides are pressed into the casting hole.

The Welch plug was originally designed in the 1900s at the Welch Motor Car Company in the United States. Prior to the invention of the Welch plug, the core holes were sealed using pipe plugs. During the testing of a car, one of the pipe plugs backed out. In order to get back on the road, one of the Welch brothers installed a press-fit quarter or half dollar coin into the hole using a hammer. The design of the Welch plug was refined based on this principle of a press-fit metallic disc.

The only disadvantage to Welch type plugs is that they're only available in steel, which rusts out. I've been tinkering with an idea to make a set of forming dies so I can fabricate brass plugs of the same design, using an arbor press or a hammer and anvil. 3/32" brass flat stock is available, and it would just be a matter of getting the right dome shape formed to make it expand and seal properly.
Jerry

Found picture of the plug you’ll refer to. See attached.
Who can tell me potential parts suppliers for this plug, seems to me it’s pretty unique.

You can purchase a whole engine set of plugs at RockAuto, look for expansion plugs in the engine section, $4 - $7 a set.

Are those mud dauber plugs in some of the other small holes?

Texas - The "welch" plugs for your 235 (both front and rear of block coolant core holes) is listed as GM# 3835121 and is 2" in diameter.

Dorman offers a replacement as Part# 550-028. This listing is for a package of 10, but you can purchase them from your local FLAPS for around $2 or less each.

Question: does the block have a step to stop the Welsh plug from going in to far?
I’m grinding away at the old Welsh plug lip and I’m afraid to damage the block’s port / boss.
See pictures

Yes - A shallow lip which I think you can see in the zoomed in screenshot from your pic. Be very careful not to grind away or disturb that as the new expansion plug won't be supported properly or seal right if ground away.

Have you tried prying out the remaining plug?

Yep! I’ve attempted but the Welch plug ring doesn’t budge.
I’m attempting to grind with a Dremel from the outer Welch plug edge working my way inboard. Slowly!!!!
Gonna take my time.

An easier way might be with a sharpened pin punch. Lay that flat against the outer bore and cut the plug ring. Once you have it cut, it should let go, being able to contract from the bore. Might take a little tapping around the perimeter to break the rust loose. If there's a little of the step cut away, that won't matter, but try to leave the outer bore un-scarred, as that's where the seal happens. Definitely use some non hardening sealant around the bore when you install a new plug.

Thanks I’ll try what you suggested. I had tried but couldn’t catch the slightest bit of the outer circumference edge. I was trying to catch a little bit of the lip but I wasn’t able to (used the corner of a wood chisel) It’s so seated that I resulted to grinding, which scares me.
Sorry but can you explain to me what you call a “pin punch.”

A pin punch is a relatively small diameter punch. If you grind the tip at an angle, it can be used as a sort of chisel.
LINK

The pictures look like someone installed a cup style plug rather than an expanding welch plug.

Here's a pic of the different types of expansion plugs, I think you're looking at the one I circled.

Well I was able to pull the rest of the Welch plug. Video speaks for itself. Unable to up load video

Glad you got it out. Have you investigated the rest of the core plugs? The one at the front of the block is same as this one.

The two on under the intake/exhaust manifold are out. The others look good.
I’m also flushing the block with pressure hose, scraping the accessible area through the water pump opening, also through the side freeze plugs, through the Welch plug hole and unclog the side drain port. Flushed the cavities with citric acid. Tomorrow I’ll flush with fresh water and a solution of baking soda.

That's definitely a cup style plug,, not a Welch plug. Someone put the wrong style in.