H2O pump rebuild saga....C2 SB

[Joe L.]

Additional Photo

Jim-----

Here is a shot of the rear of the impellers. Note that the 3704164 has a "depressed area" on the rear side of the hub. You can see this quite clearly on yours, too. The 3923250 is "flat". In the un-machined state of the 3704164, the interference fit contact area of the 3704164 and the 3923250 is about the same. However, when the 3704164 is machined down as seen in my previous photo, some interference fit contact area is lost. The intereference fit contact area of the unmachined 3704164 and the as-manufactured 3923250 is right at 1.37 square inches. The interference fit contact area of the machined down 3704164 is right at 0.88 square inches.

Still, it works for rebuilders, so it should work for you.

[Clem Z.]

if you have the seal surface of the impeller

machined down have it done on a mandrel thru the shaft hole so the seal surface is true to the shaft or you will have problems with the seal

[Jim V.]

Holy research....

Wow Joe...your research is without equal. Just got off the phone with R at LIC and he confirmed the need to cut down the original impeller. He also sells replacement seal/seats for around $6. My original impeller has a height of .846in. Rather than mess with a rather pristine 3704164...I believe I will try to scavenge up a 3923250 from an old pump. I know you said GM used the 3923250 from 68 through 75 but what pump numbers were they used on? Do you think they were used on all SB short leg pumps in that period?

BTW...do you attend any events...like the FLNCRS?

Many thanks!

[Jim V.]

will do..

...if I wind up cutting the original Thanks Clem!

[Joe L.]

Re: Holy research....

Jim-----

I think the GM #3923250 rotor was used on all small block waterpumps of the period of 1968 through APPROXIMATELY 1975, regardless of whether it's a short or long leg style pump. Keep in mind, though, that in the case of a pump that's previously been rebuilt, there's no telling what might be inside it. When commercial rebuilders do these things, they do not keep all the original components together. The units are stripped down, re-usable components cleaned, and rebuilt pumps assembled from "bins" of components.

I'm not sure what Corvette events I'll be attending next year. I might go to Florida, but I'm not really sure yet.

[Jim V.]

Got it...

I will get another seal/seat (LIC) and do the deed again using the later impeller (pictured right). Thanks Joe! I will follow up with results.