273 cast iron water pump bypass fitting size

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TimDart

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Hi all, I’m due to replace the water pump on my ‘66 Barracuda 273. The old fittings for the heater hose and bypass hose aren’t going to come out and I need to know what size NPT to bypass fitting I need.
The large threaded hole in the new water pump measures 1” across and the current bypass hose on the car has an external diameter of 1 1/4”. (Air con car)
Can anyone provide me with a size? I’m not concerned with factory correct, just want to get the job done, thanks.
 
The bypass hose fitting on the 1969 and earlier cast iron pump is 1/2" NPT.
The bypass hose has a 3/4" ID

If the threaded hole in the water pump measures 1" across then that would be 3/4" NTP
 
Last edited:
TimDart said:
Hi all, I’m due to replace the water pump on my ‘66 Barracuda 273. The old fittings for the heater hose and bypass hose aren’t going to come out and I need to know what size NPT to bypass fitting I need.
The large threaded hole in the new water pump measures 1” across and the current bypass hose on the car has an external diameter of 1 1/4”. (Air con car)
Can anyone provide me with a size? I’m not concerned with factory correct, just want to get the job done, thanks.
Click to expand...

It's a premade hose. You might have troubles with a straight hose kinking to make the bend.

engine 285.jpg
 
find a brass version and it will no longer slowly become one with the water pump.
 
694spd said:
The bypass hose fitting on the 1969 and earlier cast iron pump is 1/2" NPT.
The bypass hose has a 3/4" ID

If the threaded hole in the water pump measures 1" across then that would be 3/4" NTP
Click to expand...
Thanks, that’s what I needed
 
Thanks all, I’m over in the UK so getting parts takes a bit of searching. Appreciate the advice
 
I just replaced the bypass hose and the nipple on the Edelbrock intake manifold of my 273. I had a 3/4 NPT male copper solder fitting in there, but the stub was too short to rely on, so I switched to a 3/4" brass nipple I had. I replaced the new correct rubber hose with a silicone one (from after-market motorcycle hose kit) since I may re-install the after-market AC bracket (for York compressor) which was on the engine and it totally covers that hose (even squashes it a bit), so don't want to revisit it. I also added a heater valve which will turn off the hot coolant whenever my knee-knocker AC is on (tapped a wire inside, ran to vacuum solenoid valve). Perhaps unneeded since the heater blower will be off anyway, but figured I might copy the factory AC cars. I used a steel tube from a 1983 M-B I stripped to reduce the amount of expensive silicone heater hose, and to support the return hose on the inner fender.

Sharp eyes will note that I'm using the later aluminum water pump on my 1965 engine. Not the best choice since it is 1" thicker which made pulley alignments tricky and left little room for the fan. I was matching the only radiator I could source at the time from Autozone. I was a newbie then and didn't know all the options for sourcing parts. I also have a 1966+ 4bbl intake manifold, which has different bolt angle holes than my heads. I hogged the holes conical with a counter-sink bit on a hand drill so I could fit conical flat-top screws. Not the best approach, but made it work. Since then, I found the correct 1964-65 4bbl aluminum intake, but not going back in there yet.
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