Technical SBC Water passage head plug

Got a Gen 1 350, Target Master I think. Went to remove the plug in the head to install a mechanical temp gauge. Female square drive plug, smaller than 3/8", larger than 1/4"? Am I going crazy?

 

5/16" perhaps? They can be a pain to remove. Use the correct tool, so you don't screw it up and have to drill it out.

 

I just went through this on my sbc in my 47 buick when I changed sender locations. GET THE RIGHT TOOL! Lippy

 

I was at O'Reillys a couple hours ago, they had never heard of a 5/16" square drive. On the way home I realized I have some 5/16" lathe bits. However, I noticed the other side's head, that I wasn't going to use, had a regular hex plug, and I found a fitting that fit. So that's that. Tested the lathe bit, tight fit and plenty hard but no reason to chance it.

Thanks guys.

 

I have used a square shank punch and adjustable wrench. A punch shank is a lot tougher than a lathe bit.

Gary

 

5/16" lathe bit or key stock in a 5/16" 8 -point socket.

 

Sometimes them plugs can be a real bitch even with the right tools.

 

Mac Tools makes a set of square plug sockets. The set I have includes a 5/16”. It’s not surprising that nobody at O’really’s had never heard of one.


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A lathe bit (tool steel) is too hard/brittle, don't use it. And just because someone did in the past doesn't make it right. Key stock would work better, but the right tool for the job is always the way to go. A little heat wouldn't hurt either.

 

If it's easy to get to, a LOT of heat, some oil, and a smack with a hammer usually get them loose, so the proper tool will work to unscrew them.

Used to be one of my favorite tasks at the machine shop.

 

When I have to remove a pipe plug in a block or head I use a candle, a natural one made with bees wax. Light it and drip some wax on the threads of the pipe plug. It will wick it's way in and lube the plug making it easier to remove.

 

That bastard size plug probably cost GM $.00025 less than a plug that actually fit a wrench.

 

Target master is the problem. If I remember correctly these engines were assembled in Mexico, so it hard telling what they were assembled with

 

I use one of my Mac 1/8'' number stamps and a 12'' Crescent.

 

Regarding the5/16 square drive needed I have a Snap On torque wrench that is 9/32" drive, have heard that odd size was used during WW2. Greg

 

Speedshifter,
Yes that was a Military size. Do you have a part number? If you can post a picture of the Snap-on logo on it I can probably tell you the year of manufacture.