270 welch plug size

[harrygrey382]

Can any one tell me the size of welch plugs used on the chev/gmc 270 please?

[motto]

The five plugs along the left hand side are 1-3/16" Diameter, Cup type.
The one at the rear that is mostly obscured by the bell housing I could not measure but on the 216 Chev which I believe to be similar it is a 2" Diameter, Disc type.

David

[harrygrey382]

Thank you very much David!

[Phil Waterman]

Hi Harry

As you are asking about the size I surmise that you are looking at replacing them. Welch plug is a term that may not be as familiar to your northern CMP cousins where these are commonly called incorrectly freeze plugs. I seen a number of engines that have frozen and cracked over the years but have never seen "freeze plug" even moved. What is kind of funny is if you do a search of the NAPA parts system on Welch Plugs you find the plugs listed, but if you search on the term Freeze Plugs you get no plugs but instead all the different block heaters that go in the plug hole.

These plugs and in particular the one at the rear of the block have been the subject of Service Bulletins both as directly related to Chevy CMPs engines but also for civilian engines because of leak problems generally caused by rust. GM CMP Service Bulletin B-53 6x6 also is about the plug that covers the cam shaft bore as a source of oil leaks in the bell housing. This same Service Bulletin was reissued several times for different vehicles.

Within the last year one of the guys in our MV club had the rear one develop a major leak on his CCKW very quickly emptying the cooling system. Had it been almost any of the other plugs a roadside repair of stuffing the leak would have at least slowed the leak rate but not that location it is also the only one that requires pulling the engine to replace.

Keep us posted on your results.

Cheers Phil

[motto]

I always instal brass plugs if I can get them.
You mention failure of the rear plug as being a real inconvenience Phil. I once loaned my Chev 4403 1-1/2 ton 4x2 to a friend so as he could haul a WC51 a thousand miles home. The night before he was to begin the return trip. Water on the floor!!!!
He rapidly identified the source as being THAT plug, managed to locate a replacement and spent the night removing and re-installing the gear box, flywheel and bell housing. Fortunately he could do it that way as to remove the engine from the truck meant removing the front clip or trying to tilt the engine near vertical.

David

[Richard Farrant]

Welch plug is the term for the dished plugs with ground edge, the others are cup plugs.
They have nothing to do with releasing pressure if the block freezes, just part of the process of casting blocks. Some engines have screwed plugs.

[harrygrey382]

Thanks guys. It's actually for my uncles GMC he just acquired off a family member. He's just started it but found the welch plugs were missing. He's bunged them up with big tapered corks just to run it but wasn't sure what size to buy. I'm sure he'll get brass ones... Runs well considering how long it's been sitting!