The Stovebolt Site Forums The Shop Area Engine Shop Core Plug Replacement

Well, since Ol' Roy seems to have fixed his overheating problem on his own, I figured I may as well drive him to work today.

A 60 mile round trip on mostly interstates proved to be no problem. Temperature never came off 180.

When I got home, however,I saw a puddle of water forming under the truck. It turns out to be leaking fromthe core plug back by the throttle linkage.

I'd rather not pull the intake and exhaust manifolds to repair it. What's the best method to remove it?

Also, I want to use one of those rubber expansion plugs to close it up. What size/diameter and type do I need? I don't want to get the wrong rubber and have it melt. How far in should it be placed? I wouldn't want to block up a water passage by getting one that's too deep.

The rubber plug has an oversized flat washer that prevents it from being inserted too deep- - - - bottom the washer against the outside of the block and tighten the nut. Don't overtorque it- - - -just snug enough to prevent seep leaks is plenty. Don't use any type of sealer- - - - -insert the plug dry. Not sure about the diameter, but I can measure a block tomorrow when I've got enough daylight to see the dial caliper accurately.

Here is some information from the filling station website.

1937-1962 ENGINE SOFT PLUG KIT
Item ID: FS-529
Make: Chevrolet
This is a soft plug (freeze plug or expansion plug) kit for all 1937-1962 Chevrolet cars & trucks with 216, 235 or 261 CID engines. Set includes 4 ea. 19/32" cupped plugs, 4 ea. 5/8" threaded plugs, 2 ea. 1-5/8" cupped plugs, 1 ea. 2-7/64" cupped plug, 2 ea. 2" concave plugs. Replaces GM# 838538, 3835121

This part fits most 1937 1938 1939 1940 1941 1942 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 Chevrolet Cars and Trucks.; exceptions may apply. Please read the complete description to see if this part fits your specific vehicle and application.

Thanks but I'm not going to replace all of the core plugs. The engine is not coming out of the vehicle and I don't have enough room to pound in a brass or steel plug.

I intend to use the rubber expansion plug with the wing nut on the end for ease of installation.

I assume, from the sizes lifted above that the one I'm going to replace is 2 in in diameter. I just want to know before I knock the old one out so I can have a new one ready to go in

What would be the best way to remove the existing plug? I don't want to accidentally knock it into the water jacket. And I don't want to break it into small pieces that might fall in.

Drill a hole in the plug, put some sticky grease on the drill bit if you are concerned about metal chips falling into the block. A hole large enough to enable a tool to pry the plug out.

Don't worry about a steel plug breaking in two. You could drive the plug into the water jacket and let it rattle around in there without much issue. But Buckshot's method works as well. Drill the hole offset toward one side, so you can get good leverage with a prybar. Another trick is to get a large head sheet metal screw and drive that part way in the plug and use it to pry against.

I’m not sure you even need to drill the hole. I’ve had luck (non Stovebolt) in just driving a screwdriver through the plug and then prying it out.

Installing the rubber expansion plug is easy peasy once you’ve purchased the proper size.

Can anyone tell me what size hole that is?

It looks like about 1 3/8 to 1 1/2" in diam but it's very difficult to access for accurate measxurement.

It's the core plug behind the shift linkage, above and to the left of the petcock drain.



I'm guessing from the list posted above that it's 1 5/8".

I have a 54 235 out and on the floor and in the gasket kit the frost plugs are 1 5/8 and the hole measures 1 5/8.

thanks.

When did freeze plugs change to frost plugs? Was the change attributed to global warming?

I wonder who thought casting plugs were freeze plugs in the first place.

What should we be calling them up here in the north woods? At our lake cottage, we get 18" ice piling up on the shore during spring break-up.

Core plugs, Welch plugs, or Freeze plugs

From the article: Core Plug

"The slang term "freeze plug" was coined many decades ago based on the mistaken belief that the primary purpose of the core plugs was to protect the engine block against freezing... Only many years after they were first introduced was it found that they sometimes acted to reduce the possibility of the cracking of the engine block during a freeze."

ol 55 is correct. Their only purpose is to support the casting core. Without them, there would be no way to cast the inside passages for cooling an engine block.
As far a freeze protection, when water freezes inside a block, the place that gets the most pressure and where the crack happens is the LAST place that the water freezes. The typical crack in a Stovebolt block is along the left side of the engine at the lowest point of the water jacket, not at the core plugs. Water in a lake freezes from the top down, and likely the same thing happens in an engine. It's a property of the density of water as the temperature changes, and the reason that icebergs float.

I replaced the plug yesterday. It was so rusted, I pushed a hole through it pretty easily. The "ring" of the plug remained firmly stuck in place so I used a Dremel cutter to remove the bottom of the cup and smooth out the edges.

I was afraid to try cutting the ring in case I couldn't get it all or left a rough surface that wouldn't allow the rubber plug to seal.

I'd post pictures but my phone doesn't want to download pics to my computer.

I took out the petcock as well and flushed out a little crud.

Next up is removing the leaking JB Weld on the crack and replacing it with MarineTex.

I am in the middle of rebuilding a motor. The motor is original, never rebuilt, just shy of 60 years old.

My machinist is a young guy, terrific really. Tolerates all my inline nonsense. I was ordering some parts. Now mind you, the core plugs were not leaking or damages, I just replace them as a matter of course and I have a couple of the Pioneer kits in steel at home.

He was recommending a brass freeze plug set because it was more rust resistant. I am 64 so I said bless your heart but I wont be around when the steel set I am installing goes bad, lol.

Otto... It's been my experience that when one rusts through, the other three aren't far behind. When a 216 I had dropped it's water back in '01, the front domed plug had rusted out. Pulling the engine, I was able to stick my pocket knife through the front welch plug and push a screwdriver through the rear Welch. The one under the bell housing was not as bad.
So... watch out.

This scares me. Our 216 engine left front freeze plug started leaking and the engine is still installed. I considered using a leak sealer.

So far so good. The one I replaced had visible rust on the outside. The other one looks really good and feels strong when I press on it.

About all leak sealer is good for is clogging up radiators. Bite the bullet and do it right the first time. If the leaky plug is on the side of the engine, it's not very difficult to change it- - - -especially if you use a rubber expansion plug.
Jerry

Thanks Jerry
Would any auto parts store have the rubber plugs? I measured the I.D. Of the port and it’s approximately 1.5”

Your local parts store will probably have them. If not, there are dozens of them on Ebay. Once you get the leaky plug out, clean the block bore with sandpaper and install the expansion plug dry- - - -no gasket sealer. It needs to get a good bite on the block.

www.ebay.com/itm/335578967293?

Jerry

Texas, Your pressed in plug is stamped 1-5/8". A 1-1/2" plug would probably expand enough to fill the hole, but may not seal as well as a 1-5/8" plug. As Jerry mentioned, they are easily available at most FLAPS or ordering on-line. Sample web search result below.

Thanks to you’ll.
I’ll definitely follow you’ll recommendations.
I’ll report back

I bought a pack of 5 on Amazon for about $7 and free shipping. Here's a crappy picture of it installed.

Send me a PM and I'll mail one to you, although you'll probably find one locally sooner and for the same cost as the US Mail.

Well this weekend we replaced the leaking core plug. I did purchase the core plugs from Amazon but by mistake I ordered a box containing 5 plugs for 12.95, didn’t use them since my local Auto Zone had excess inventory and purchased the metal ones. Considering that the front clip is off the truck we opted to install the metal core plug.

While removing the original core plug it got hairy and used a coat hanger to hook the plug, catch the plug’s edge with a vise grip pliers and pulled it out.

Though I had drained the radiator coolant came pouring out. For your information our rear engine block drain is not to be messed with, since decades ago someone had probably messed up the blocks thread, installed an oversized fitting and capped the pipe.

I used a basting suction tool to extract coolant and whatever rust residue that was inside the block near the core plug hole.
Sorry for the drawn out detail.

Detail is good. We all want to hear what you encountered replacing the plug, so we know what to expect if we run into the same situation.