Block drain plug size?

[Talkwrench]

Guys, what size are the coolant drain plugs in my 37 block?
I attempted to take them out this morning but both are damaged already and I had to try with vice grips .. Wouldn't budge. Any tricks?

Thanks

[Reds34]

Do you currently have coolant in the engine? They are either 1/4npt or 3/8npt, can't remember which one.

Red

[Talkwrench]

The will be a small amount left, has been drained for the radiator and pumps replacement. Thought I would get the plugs out and replace them while at it..

[Reds34]

You may be able to put some penetrating oil on the plugs from the inlet of the pumps. Maybe heat would help? I suppose you could drill them out if you have to.

Red

[JM 35 Sedan]

I just removed those threaded plugs on a '37 block that is being rebuilt for use in a '34 PU. These were factory installed plugs (not petcocks) that had never been removed and they were very tightly locked in place. I first tried using a hand held impact driver with a 3/8" internal square fitting and this was rounding off the square corners of the plug instead of threading it out of the block. Had to use heat from a gas torch on the cast area around the plug to finally get those plugs to thread out of the block.

[Walt Dupont--Me.]

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If the engine is in the car and you cain't get the plugs out, NEVER leave water in the block even after you remove the radiator if you live in a cold part of the country. There will be just enough water in the bottom of the block to crack the block the whole length on both sides inside just about 1/2in. above the pan rail. make sure there is anti freeze in the block. Walt

[Bruce Lancaster]

Start by drilling through center of plug, being careful to hit correct angle and as close to actual center as you can manage. Plugs like this in my experience relax a bit when center is gone and sometimes become quite easy to unscrew. If no luck, keep drilling, going up in small increments in size and then closely examining your hole with a powerful flashlight after each enlargement. Once you see the first trace of threads peeking through it's time for creative violence until it relaxes and lets go. A dremel with a small bit might be a way to keep going here.

[Talkwrench]

Walt your kidding me..?? Its winter here but we dont have freezing conditions, lucky. I use a product from Nulon [R45] its a coolant that doesnt have glycol in it [can be used for racing].
Block is in car so drilling it out would be near on impossible as the cross memeber is in the way.. Maybe next time its on a hoist I could have another crack at it..

[trevo]

Winter in Australia is fabulous Brisbane was 1deg at 7am 30 by lunchtime why do you want to remove the plugs can you get by without doing that they are bound to be frozen that is rusted to form a solid union as others have said drilling and re tapping but you have the cross member a tricky one!

[Bluebell]

They can be a real bugger to get out, if they break off.
Brass rounds off easily, breaks easily, and won't come out with ordinary easy outs. It just spreads.
So if you don't need to have it out now, it might be better left alone.
Just my 2 cents.

[Talkwrench]

Yeah its a bugger! I think in that case I will just leave them alone.. Reason for taking them out is when it comes to flushing the block and cooling system I would not have to take those damn lower radiator hoses off.. Man I would sooner remove the radiator again than huffing and puffing and busted knuckles to get them on and off!.