Corvette Water Pump, Sb, 1956 on 2040-parts.com

Here's a professionally rebuilt GM 3704911 water pump as installed on '56 Corvettes.  While this pump casting wasn't dated, there were several foundries that produced it and this one's correct for Corvette engines being a Saginaw/Flint vs. Tonawanda product.

Note there is an upper boss which is NOT drilled & tapped for an external bypass nipple.  This differentiates this version of the casting from that used on '55 Corvettes.  The '55 version of the casting had no upper boss at all.  The version with the boss debuted in '56 and it was not drilled & tapped for an external bypass in the pump's Corvette configuration.

When I first saw this pump core in the rough, I thought it was freeze cracked. Look at the rugged line at the top of the pump. Look more closely and you'll see the line makes right angle bends on either side of the newly added upper boss. I suspected what I had here was a very early '56 pump cast right after the mold had been reworked to add the new for '56 upper boss structure. That the 'crack' was actually a casting fill flaw around the parting line in the mold where the rework had been done.

When the pump was cleaned the series of lines surrounding the 'crack' became obvious. And, when the pump was apart with the shaft and impeller removed, the back side of the 'crack' was easy to see--there's NOTHING there! So, this confirms my hunch that this isn't a 'crack' and what we have here is a poor fill of the mold that reveals the changes made to make the 1956 shape.

Note the correct factory concours details of a flat rear plate and slot-head screws.  This pump is ready to bolt on and paint and comes with a 30-day warranty!

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