6v temp sending unit in 57 heads

[41Fordor]

Hi all, I have another dumb question. My 292 has 57 G heads, but is in a stock 6v 54 Customline. The 12v sending unit standard in 57 is of course a different thread size and function than the older 6v sending unit. The gauge starts pegged at H but moves backwards to C as the engine heats up. No overheating or boiling over so I'm not too worried.

Is there an aftermarket or replacement style that will go in the smaller threaded opening in the 57 heads but still work with the older 6v dash?

Thanks!

 

[paul2748]

The sender is screwed into a bung that is pressed into the head. These are removeable. There are two sizes that I know of. The pre 57 sender thread size and the 57 and later sender thread size. Both bungs are available from the old car suppliers. One I know for sure is CASCO, the Tbird parts supplier. I am pretty sure the other suppliers have them.. Also available is a tool to remove the old one.

In my 54 ( 312, converted to 12V)I have the same situation as you. I decided to leave it as is and just note where the needle sits at normal operating temperature . Got too lazy to change it.

Not a dumb question at all.

 

[dmsfrr]

My '55 has later heads also and needed a refit for the larger original sensor.

The press-in bushings are replaceable but they are a softer metal than the head and easily drilled out and rethreaded.
They both are tapered 'pipe thread'. 1/4" for '57+ and 3/8" for '56 and earlier.
If memory serves use a 9/16" bit on the bushing then the 3/8" NPT tap.

There is a portion of the cast-iron head on the lower rear side of the hole you'll be drilling so keep the bit square with the head, or angled very slightly toward the front. This helps the larger longer sensor fit more easily.
A helper with a shopvac and narrow nozzle as close as possible to the drill bit & tap can keep filings from dropping into the water jacket of the head.
.

 

[41Fordor]

My '55 has later heads also and needed a refit for the larger original sensor.

The press-in bushings are replaceable but they are a softer metal than the head and easily drilled out and rethreaded.
They both are tapered 'pipe thread'. 1/4" for '57+ and 3/8" for '56 and earlier.
If memory serves use a 9/16" bit on the bushing then the 3/8" NPT tap.

Haha, I'm not brave enough to do that. Of course, I should have done it while the motor was out and disassembled, if I'd been paying attention.

 

[rotorwrench]

Pipe threads can be difficult to tap. I sometimes start with a tapered reamer to more equalize the cutting forces. It's a learned experience about how far to go with the reamer so I measure the valleys of the threads at the top and bottom of the item to be screwed in whether a plug or fitting. This give information about how far to go with the reamer. Use grease to catch the shavings as best you can and constantly remove the reamer or tap to clean the crud. It ain't perfect but it gets the job done.

Drilling before cutting should be limited to the size of the tip thread valleys of the sender. Maybe even a bit smaller just too be sure. Straight threads are much easier to cut but a lot of aviation fittings are still tapered pipe so that's where I got the experience. Cast iron is harder than aluminum castings so it's even more challenging.