Technical What fits this hole in my GMC head?

Tried using a 3/8& 1/2" extensions but one is big and 3/8 is loose. Plug in the head. How do I get this removed?

Thanks

 

I was told the temperature sending unit needs to go there...

 

The safe, long way would be to drill out the center than use a hacksaw blade to cut out to the threads in two or three places. Than you can remove the segments with a chisel. These plugs can be really frozen in there. Yes, good place for temp sender.

 

Take an old 1/2" short extension and grind it to fit. Try some heat and an impact on it if it won't move with a breaker bar.

 

I'm curious, what's wrong with where the sending unit is now?

 

So... You really do need a hole in the head? . ( Sorry, couldn't resist. )

 

Agreed

 

I'm the guy who told him the rear hole is not for the temp sender. It's for a water line which goes forward to the thermostat housing to move coolant from the hottest spot in the engine. The larger 302 trucks were built like that. The one he is taking out is for the temp sender.

. dtwbcs wrote he as having a cooling problem since has more compression than stock and is actually reading the hottest spot in the engine. With the added return flow to the housing and the sender in the correct place he (possibly) will not have a cooling problem at all. Until I found this after racing these engines for years I thought I had this problem too. No more.

I removed this plug by grinding a 6 inch 1/2" extension to fit tight and a long ratchet or breaker bar.

 

So actually your saying he really don't have a heating issue just a temp sender reading in a Hotter spot than it should be?
The Wizzard

 

No. He should be removing water from the place where the temp sender is now and move the temp sender to the hole indicated.

 

Great info, thanks.

 

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If I drill &cut it out will it hurt if it falls inside the head? Still would like to get it removed as one piece of possible


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That rear hole is for a water line that goes to?


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Those types of plug can be difficult to remove probably ben in there since vehicle was new. Can try welding something to it them let it cool and remove it. Only if all else fails.

 

I think I got it. Sounds now like it's lack of circulation creating higher temps just at the back of block. Moving that water back to front just increases circulation to drop spot high temp. Am I correct now?
The Wizzard

 

If your going to try this method do Not ground your welder to any motor part. The ground transfer can fuse the plug permanently in the head.

 

They actually make a tool for removing that plug. Used to get them from Snap On but you should be able to find one at an autoparts store. You can use it for a sender or to pull water for your heaters or use it for one end of your electric block heater if you live where it is really cold.

 

If I did this would the pieces fall inside& hurt internally?i feel it was put in New in around 1950 GMC302


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You got it.

 

This is the ticket. I bought a 396 already assembled and someone put the left head on the right side and vice versa. The problem being the temp sender goes in the left head and it had a plug in it like the one you are playing with. Frozen in over time it was going to be a fight. I did it by cutting a steel nut in half to make sure I got full penetration with the TIG welder, welded the nut to the plug (glowing red) and backed it out with an impact wrench. That stuck plug was no match for the combination of the intense heat and the impact wrench.

 

Before I cut the plug into pieces, I'd definitely try to unscrew it. I'd try a ground-down extension with a lot of heat and if that doesn't work, I'd weld a nut to it....unscrew as soon as the red goes away.
It would be my luck to screw up the threads trying to cut the plug out...then the pieces would get caught in my water pump.

 

My wife is constantly asking if I have a hole in my head, or want another one, but there's no GMC involved...

 

Before I screwed up an 1/2 inch extension, I would use a piece of 1/2 square stock and grind that to fit. My Craftsman socket set has a 1/2 square socket and a 1/2 12 point spline kind of socket that fit 1/2 square quite well.

 

If your thermostat housing has a plug on the right and left side it is correct. The right side had a heater hose fitting and the left went to the the rear of the head. Now some thermostat housings did not have a left side plug and you need to find one. They were not only on large truck GMC's but on standard Chevrolets that used that plug for their electric temperature senders (idiot light) on the later 235's. I always use 90* fittings and a straight piece of tubing with short hosed pieces for this. I make brackets that are attached to the intake/exhaust manifold study to support it.
Also on drilling out of a plug on any engine, use a lot of grease on it drill if this needs to be done. Same with a tap. When this plug need to be done like this, the hole is large enough to use a magnet to remove any shavings.. I have never needed to drill one out.

 

So I bought a half inch extension that I guess I'll grind down to fit that opening. I could not find a square head socket at Sears


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Give a few good smacks nice and square on top with a heave hammer before you try.
If you have the stuff to pre-heat and weld something on it I would just start there. JMO

 

Here is the best method I have found...
Find - make ..borrow the appropriate socket..
Take your oxyacetylene torch and heat the center of the plug red hot.
Turn off the torch..
Melt some paraffin wax on the hot plug..
It will smoke..
It will run off...
Keep adding more wax..

As it cools it will wick down the threads..
Let it cool until you can touch it.
It will screw right out..

Taught to me by a very crusty marine mechanic...
If you have ever worked on salt water boats...you know what corrosion REALLY is..lol

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If you have to drill, pack the flutes of the drill with grease and go slowly. The grease will retain the drillings


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its a 7/16 pipe plug the tool kit is this that we use for them (below ) sunex 2841 ( amazon , summit racing ) , have to be carefull removing them as they are tapered ( the plug and the threads ) , we heat them up with a torch then bees wax and center punch it and then back them out , if you bugger it you can put valve grinding paste ( best) or colgate standard toothpaste ( white stuff) or a mixture of water and comet in the hole to help make the tool grab better .