Broken temp sender unit

A

Al NJ

Member
I have a broken temperature sending unit in a '39 cylinder head.
It's broken below the surface, nothing to put a wrench on.
Should I just drill it out with progressively larger bits until I can just peel out the remains?
I did a search but couldn't find anything. Any help would be appreciated.
Thanks.
 
Sorry, I should have been more clear. The head is off the engine.
The bulb part is still in the head, but whats left of the bulb is about 3/8" below the surface.
I would imagine there aren't a lot of threads left engaging the head. ???
 
There are extractors for broken pipethreads that should be able to fit the job.
If you got a plumber in the neighbourhood you can borrow one from.
Otherwise just drilling/grinding and taking out the threads should work...
 
Al NJ said:
Sorry, I should have been more clear. The head is off the engine.
The bulb part is still in the head, but whats left of the bulb is about 3/8" below the surface.
I would imagine there aren't a lot of threads left engaging the head. ???
Click to expand...

Al.Here is a pic of what that assy should look like when installed.In this case the line for the bulb has been cut.So yours is broken off just below the hex?
 

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Thanks for the picture! Mine's broken off about 3/8" down in the head. In other words I can see about 3/8" of the female threads in the head. Looking at the picture I would guess there's only a couple of threads left on the sending unit that are engaged in the head, if it's the same type of sending unit.
I shot it with a little PB Blaster. I'll probably start drilling after dinner.
 
Al NJ said:
Sorry, I should have been more clear. The head is off the engine.
The bulb part is still in the head, but whats left of the bulb is about 3/8" below the surface.
I would imagine there aren't a lot of threads left engaging the head. ???
Click to expand...

What I would do-
Take a hacksaw blade and cut through the side of the brass until you see signs of the 3/8" pipe threads- DON'T cut into the cast iron. Move over 1/8" or so and do it again. The piece in the center of your two cuts (1/8" wide) can be peeled out toward the center of the hole with a punch sharpened on an angle. The remnant can be unscrewed.
(You may have to grind off the back of hacksaw blade to fit into the fitting)

Karl
 
One good thing about tapered pipe threads is the taper. If the right size drill is selected, a person could drill it out and only affect the last few turns of thread in there. Drills in fractional and letter sizes (alphabetic) can get you some precision there. Or you can try easy outs first. clean the thread bore as good as you can before the attempt. Bead blast lightly if possible & clean that out as good as you can. Tapers wedge themselves in pretty well so drilling or peeling the shell might be the best solution.
 
I don't have an original head here to look at but I'm wondering if you can get at this from the back (inside). Maybe you can get a better grip on what's left of the sender.
 
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