The Stovebolt Site Forums The Shop Area Engine Shop Freeze plug question

1956 Chevy 3100 pickup with 235 engine:

Well, I managed to remove all the freeze plugs without much trouble. They didn't pivot like some said they would. Mine just dropped down inside so I used a magnet to bring it up where I could use vice grips to remove them. Now it's just a matter of doing a super cleanup of the surfaces.

What surprised me was that both of the large plugs in the back of the engine appear to be oil plugs versus water jacket plugs. One at the back of the cam bearing appeared oily and the large, nearly flat disc plug was coated with oil grit. Plus the opening had a large amount of caked oil sludge covering half the opening that I pulled out. Inside this one there was a large amount of sludge buildup that I removed as much as possible. I plan on pouring gasoline down inside it to loosen up more and then shoot air inside for cleaning.

My question is why freeze plugs for two areas that evidently are oil areas and not water jacket areas?

First of all, the phrase "freeze plugs" is a misnomer. They're casting plugs. They aren't put there for any reason other than to aid in the manufacturing process.

All of those openings, including those in the water galleries, are cast into the block so that the sand from the mold can be emptied out after the iron hardens.

Hawkman - The two plugs on the back serve different purposes and are supposed to be different designs as well.

Looking at the rear of the block, the plug on the lower right is in fact the camshaft bearing plug (GM# 3704158 - Plug, cam shaft bearing: 2-1/8" diameter x 1/4" thick cup style) which fits 1954-62 Chevy 235 and 261 engines, not to mention most other Chevy engines. It's exposed to the oil lubricating the rear cam bearing and not unusual for sludge to be found back there if the engine wasn't well maintained.

The plug in the upper center of the block is for sealing the coolant passage core opening (GM# 3835121 - Expansion plug - drain, cylinder block (front and rear 2" diameter). AKA - "Welch Plug" which is not a cup design, but a convex disc that expands to seal the opening when struck in the center which expands the diameter to seat/seal against the core opening. The sludge behind that plug shouldn't be oily, but coolant can have an oily/slippery feeling.

I recently posted about the plugs in a couple other threads, noting that Dorman offers a replacement for the 2" coolant core plug as Part# 550-028. That listing is for a package of 10, but you can purchase them from your local FLAPS for around $2 or less each. Note: By 2 as these fit both the rear and front core openings on your block.

For the camshaft bearing plug, Dorman lists the replacement for GM# 3704158 as 555-049. Also available from your local FLAPS.

The only "freeze" plug that is exposed to oil will be the one behind the camshaft. The rest of them, including the two large flat plugs at the front and rear, cover casting holes in the water jacket, also the ones down the driver's side of the block. There are two very small plugs (like about 1/2"-9/16") at the ends of the oil pressure gallery. I like to tap those holes for a 1/4" pipe thread and use screw-in tapered Allen plugs instead of press fit ones during a rebuild.
Jerry

I learned a whole lot in a short time. Thanks Hotrod Lincoln,Gdads51 and Otto Skorzeny. It makes sense, but the Welch Plug really has me worried for how much oily muck was in the cavity. Again, thanks for your quick answers and always greatly appreciated. Will let you know if I find somethink out of sorts on that Welch Plug area.

Now would be a good time to take the block to the car wash for good cleaning. Power wash the coolant area and the oil galleries as much as possible. Presoak the block in simple green or your choice of degreasers. The water passages can be poked and scraped with what ever tools you can get in there with. If you have a power washer or can one, use the RED pinpoint tip to really get into the depths of the coolant areas, be sure to remove the drain plug at the back and back flush though the opening. A wire brush on a drill motor makes fast work of cleaning the block openings and de-rusting the rest of the block. The degreasers will clean the inside.

The small plug that's visible at the left side in Gdads' photo is for the oil gallery, and there's a corresponding plug at the front of the block. That's the passage that I like to thread for pipe plugs, as they are exposed to full oil pressure and I believe a threaded plug is more secure. That passage can be threaded with a 1/4" NPT tap without doing any drilling- - - - -just flush out any chips thoroughly afterwards.
Jerry

Has anyone used a freeze-plug block-heater with it's compressible rubber O-ring to plug up these holes without ever plugging them in electrically? (Sorry, I use "freeze -plug" like everyone I know. If I said "casting plug", they would say "Huh?".)

I installed a block heater in one of the core holes, but haven't plugged it in yet. For the cost of the block heater, I wouldn't use them in place of normal core plugs. A guy could do that for 3 of the 5 core holes, but not the two on the rear of a 216. The cam would interfere with the one at the end of the cam, and both would prevent the bell housing from mounting flush with the block.

Use Permatex to seal the plugs, Form-a-gasket #3. Its the non hardening dark brown stuff, a light coating around the plug is all thats needed. Its not hard to install plugs, just use a big socket to drive them in, but not so big they get stuck! I used a socket that just fit in the plug, not considering the plug will get smaller as it goes in, it got stuck really tight. I ended up driving it into the block, then pulling the socket back out and digging the plug out sideways, a trip to the store for a replacement was needed.
Press them in just flush with the block or slightly below, I go just till there is no lip or edge showing where dirt and grease could get caught.

Over time the rubber o-rings on meter start to seep.