66 BB water pump

[Richard S.]

Are the thread sizes the same for both the heater hose fitting....and the by pass hose fitting in the water pump itself? My by pass hose fitting seems to have a smaller thread than the heater hose fitting....I broke a fitting and need to find another one but the good one I have from the heater hose hole won't thread into the by pass hole....is it because the thread size is smaller?? Thanks for the help.

[John L.]

Re: 66 BB water pump

Rick -- I think the fitting you mention is pressed into the housing.

[Richard S.]

Re: 66 BB water pump

John,
It is a threaded hole......in the water pump.....help.....

[Stephen L.]

Re: 66 BB water pump

On a 67 BB (I assume they are the same) The thread size for the water bypass is the same as the thread size for the heater hose on the water pump; 3/4 inch NPT.
The heater hose fitting that screws into the manifold is the same size threads but the internal diameter and hose diameter is smaller; 1/2 inch.

You need an internal diameter of 5/8 inch for the bypass hose with 3/4 inch NPT threads. NAPA may have it.

[Richard S.]

Re: 66 BB water pump

Thanks Steve.....

[John L.]

Re: 66 BB water pump

Rick - The 66 BB water pump's bypass fitting is pressed in per the judging manual. It would appear that either you have a non 66 original pump, a 66 pump rebuilt with a threaded bypass hole, or a non GM pump. In either case -- good luck with it -- hope you get it running.

[Richard S.]

Re: 66 BB water pump

Thanks John......

[Richard S.]

Re: 66 BB water pump

Thanks for the help guys.......I found what I needed. The threads are the same size and that is 1/2 inch NPT.

[Joe L.]

Re: 66 BB water pump

Rick-----

What's the casting number of this waterpump? It should be 3856284. This casting was used from 1965 through early 1969. I am not aware of any original 3856284 pump castings that used a threaded bypass fitting. There may have been some, but I'm not aware of it.