AC Water Temp Gauge Fittings

[Gearbox]

Hi all;

 

Have a bit of a head scratcher that I hope the more experienced can help me out on. I have collected all the period correct gauges for my 1962 Lotus Super Seven and now figuring out how they are fitted. The question for today is about the water temp gauge. I am assuming that the sender is inserted into the water pump. There is a 5/8-20 threaded bung on the water pump outlet. The sender has a 14 pitch thread which I had assumed was a 1/4 NPT, but the 1/4 NPT has a 18 pitch thread. So I looked at BSP sizes and see that it also has a different pitch of 19, and the only pipe threading which has 14 pitch was 1/2 which as we know, is like 3/4" in diameter and way too big. The diameter of the threads on the sender is about 9/16 but normal threads would be 12, 18, and 24. So I am at a loss or missing the obvious. Any help ot there? thanks Allan

[coffee break]

Since the gauge reads centigrade, might the thread be metric?

[escondidoron]

Hi Allan;

 

the sender bulb is not supposed to screw into the water pump. Instead it should fit into the cylinder head on the left side at the front corner, just in front of the #1 cylinder exhaust port. See picture of my 109E (Cosworth) below:

If you zoom in closely to the front left corner of the head you can plainly see the sensor line where it goes into the head. Look just below the swirl pot to radiator tube to the right and above the home made stainless steel line that runs from the air cleaner plenum backplate to the crankcase vent port on the distributor side of the block.

 

While there are several modifications from original '62 spec to accommodate the air cleaner assembly that are visible in the picture, the AC water temp gauge and its fitment in the head is original as are the Cosworth intake manifolds / linkage and Webers.

 

Good luck.

 

Regards,

[Gearbox]

Ron;

 

Thank you, I'm using a 116e head that had been flowed with larger valves and see that it has a 1/8 NPT threaded hole that is too small for this gauge. I could easily drill another hole and thread it, but have no clue on what thread size to use. The thread on the gauge has a 14 pitch, and measures about 0.60" across the threads and I have yet to figure out what this thread is. It doesn't match any standard NPT sizes nor BSP sizes. So I am still stuck, any ideas? Also, is the water pump thread hole just closed up with a threaded cap? Thanks again Allan

[Gearbox]

Just to wrap up this thread, I finally figured it out. I found the original 109e Cosy head and the port was there, thanks Ron. But after cleaning it up a bit, it struck me as fine threads. So of course I threaded the sender into the hole and eureka, it threads in perfectly. Go figure, I checked the threads again on the sender and the 18 pitch gauge didn't look like it fitted, but again the 14 was much closer. But the thread in question was a straight 5/16-18 thread. Didn't realize that they would had used a standard thread for a water jacket and not a pipe thread, but see that the design was where the brass sender tube has a step which seats on the block, so when the nut is tightened, it seals the tube from leaking, so the threads didn't need to have a water tight seal. But now this raises another issue, the 116e block has a much thinner wall where the hole goes so it will be difficult to drill a stepped hole and then expect to have the nut tighten all the way. So I figure tap the head with a standard 3/8 or 1/2 NPT, and get a 5/16-18 female and NPT male adapter and hope they make one with the stepped bore I need. The fun just never stops lol. Anyway, thanks for the help and you know what they say, even a broken watch is right twice a day.