608 Water Pump GM # ?

[Gregory G.]

What does the Casting of GM1 & GM5 identify ?

I have seen GM31.

Greg

[Harry S.]

Re: 608 Water Pump GM # ?

Typically it's the mold number to cast the part.

[Gregory G.]

Re: 608 Water Pump GM # ?

Does the mold number correspond to a production time line ?

[Joe L.]

Re: 608 Water Pump GM # ?

Does the mold number correspond to a production time line ?

Gregory------


Technically, these are actually pattern numbers. With sand castings, patterns are used to make the sand molds. Patterns are used until they wear out and are replaced with new patterns of a different and, usually, higher number. The numbers VERY ROUGHLY imply the period that they were first used. The '608' waterpump was being manufactured from 1957 to 1970 for PRODUCTION and even later for SERVICE. These waterpumps were used on millions of Chevrolet small blocks and there were undoubtedly many patterns in use at any given time and many replacements over the period.

The very first '608' pump cast was probably from pattern "GM1" although there were likely at least several patterns in use from the beginning (e.g. GM2, GM3, GM4, etc.). Some patterns may live a long life and some may "die" quickly. The original '608' waterpump on my original owner 1969 was pattern number GM27. So, I would say that GM31 was likely from the late 60's period. However, dating a casting by pattern number is, to say the least, a VERY IMPRECISE science. A better method is simply to refer to the casting date, assuming the casting has one.

By the way, pattern number prefix "GMT" indicates a Tonawanda foundry pattern. So, for example, a "GMT1" is a completely different pattern than a "GM1".