Small Block Water Pump Hubs

[Joe L.]

There was a recent question regarding water pump hubs. So, I thought I'd start a new thread and post some information and thoughts on this subject.

During the 1955-68 period (and through 1970 for Corvettes and some MD/HD truck applicationsonly), all small block waterpumps were "short leg" and used a shaft /bearing assembly with a 5/8" OD shaft, end-to-end. Consequently, all waterpump hubs had a 5/8" shaft orifice. During the period of 1955 to ABOUT 1965, I believe that all Chevrolet applications used a pulley/fan bolt circle of 1-3/4". So, I believe that during this period all SB waterpump hubs, PRODUCTION or SERVICE, had a single, 1-3/4" bolt pattern.

After ABOUT 1965 and through 1968 some Chevrolet applications (but not Corvette) went to a 2-1/8" bolt circle. During this period, PRODUCTION waterpumps for such applications probably used a single 2-1/8" bolt circle hub (I really don't know, for sure, since I don't really study non-Corvette applications). However, SERVICE waterpumps began being fitted with the dual pattern hubs because, except for the hub bolt pattern (and, sometimes, hub spacing), the pumps were otherwise the same.

For 1969-70, things changed. The PRODUCTION use of the short leg waterpumps was drastically reduced as most applications changed to the "long leg" style waterpumps. The only exceptions were Corvette and some MD/HD truck applications. It's during this period that I believe some PRODUCTION waterpumps will be found with dual pattern hubs. Most likely, this occurred because with the drastically reduced requirements for short leg waterpumps, there was much less of a cost savings incentive for different hubs being used for PRODUCTION and SERVICE.

For 1971 things changed again. All Chevrolet SB waterpumps went to a 3/4" shaft bearing assembly. While most applications used a "long leg" style pump with a 5/8" pilot, the shaft through the bearing and through the hub was 3/4". Corvette and some MD/HD trucks were the exception. They used a short leg pump body (but somewhat different than the pre-71 short leg body) and a 3/4" pilot. So, the waterpump hub for all 1971+ Chevrolet applications had a 3/4" orifice for the shaft. So far, I have never seen a hub for a 1971+ Chevrolet waterpump, PRODUCTION or SERVICE, with anything but a single pattern, 2-1/8" bolt circle. Why? Well, I expect it's because there was never ANY Chevrolet application ever made which used a 3/4" shaft waterpump with a 1-3/4" bolt circle. So, why incur the extra cost of manufacturing 3/4" shaft hubs with 4 extra tapped holes?

By the way, while 1955-1970 waterpumps used a 5/8" shaft through the bearing and hub and 1971-82 used a 3/4" shaft through the bearing and hub, ALL 1955-82 waterpumps used a 5/8" shaft inboard of the bearing on the rotor end.

[Richard M.]

Re: Small Block Water Pump Hubs

Joe, Very informative, thank you.

Were these hubs available as a separate item as Service replacements from the Parts Departments? I looked for some part numbers but couldn't find them in my books. Do you have their part numbers for the various configurations? Are they still available?

In my years of rebuilding water pumps, I typically use new hubs as supplied with the rebuild kits, but on occasion I had to use the originals to maintain proper 4 hole configuration with the 1 3/4" pulley mount hole spacing, as some kits included the 8 hole types. Another issue is the quality appearance of the hubs in the newer kits, or might I say lack of quality. This being another reason I often prefer to use original hubs. The force required to either remove or install these hubs is tremendous and requires a hydraulic press. Their press fit design prevents slippage.

The new rebuild kits on the market today are different from original rebuild kits, both early GM or early aftermarket, as their bearing assembly shaft diameters and hub and impeller ID dimensions do not match. The seal assemblies are a completely different design as well. I've outlined these differences in a document. One cannot use original cast impellers or original hubs using the new shaft/bearing assemblies as their diameters are different. Most new kits include a stamped steel impeller. I always attempt to use original cast impellers as they are more robust than the stamped steel type. The dimensional difference of the shafts in some of the new aftermarket kits often disallows this.

Rich

[Joe L.]

Re: Small Block Water Pump Hubs

Joe, Very informative, thank you.

Were these hubs available as a separate item as Service replacements from the Parts Departments? I looked for some part numbers but couldn't find them in my books. Do you have their part numbers for the various configurations? Are they still available?

In my years of rebuilding water pumps, I typically use new hubs as supplied with the rebuild kits, but on occasion I had to use the originals to maintain proper 4 hole configuration with the 1 3/4" pulley mount hole spacing, as some kits included the 8 hole types. Another issue is the quality appearance of the hubs in the newer kits, or might I say lack of quality. This being another reason I often prefer to use original hubs. The force required to either remove or install these hubs is tremendous and requires a hydraulic press. Their press fit design prevents slippage.

The new rebuild kits on the market today are different from original rebuild kits, both early GM or early aftermarket, as their bearing assembly shaft diameters and hub and impeller ID dimensions do not match. The seal assemblies are a completely different design as well. I've outlined these differences in a document. One cannot use original cast impellers or original hubs using the new shaft/bearing assemblies as their diameters are different. Most new kits include a stamped steel impeller. I always attempt to use original cast impellers as they are more robust than the stamped steel type. The dimensional difference of the shafts in some of the new aftermarket kits often disallows this.

Rich

Rich------


As far as I have been able to determine, the hubs were never available in SERVICE from GM although most of the other waterpump components once were so available. It's possible they were available through Delco, but I kind of doubt it.

I expect the current bearing assemblies may be metric. That may be why fitment doesn't work with original components.

The cast impeller is definitely superior to the stamped steel variety. Unfortunately, many impellers from original pumps have suffered
major erosion of metal due to corrosion and cavitation damage. I've seen some that were ridiculously "thin".

[Richard M.]

Re: Small Block Water Pump Hubs

Thanks Joe, I couldn't find a separate part# anywhere for the hubs. I looked once for a 4 hole hub for the 3/4" shaft and never found one. Now I see from your information they were never available.

I then "fabricated" my own, a 4 hole 1 3/4" spaced hub for the 3/4" Big Block shaft. This was on a 1967 water pump on a L71 435hp that uses the 3/4" shaft. The BB pump date code and part# is difficult to see, but if the hub is a 8 hole it can often alarm the curious. The rebuilt original dated pump came to me from a West Coast water pump rebuilder but it had the 8-hole universal hub on the 3/4" shaft. I liked the idea of the improved 3/4" shafts for strength, albeit not originally used.

The hub can be seen by using a mirror at the back side of the pulley if judged. So we decided to use the 4 hole hub rather than rebuilding the pump and replace the bearing/shaft assembly with the less robust 5/8" shaft.

I lathe bored the ID of a new 4 hole hub with the 5/8" ID to the correct spec for the 3/4" shaft size and pressed it onto the shaft. That pump has been on the car for 6 years with many thousands of miles and has performed flawlessly.

Below you can also see the 3/4" shaft with the 5/8" pilot as mentioned for the pulley and fan clutch. I forgot I had these photos and your post prompted me to look for them.

Apologies for digressing somewhat from the small block discussion, but some information may be generally applicable.

Rich

[Joe L.]

Re: Small Block Water Pump Hubs

Thanks Joe, I couldn't find a separate part# anywhere for the hubs. I looked once for a 4 hole hub for the 3/4" shaft and never found one. Now I see from your information they were never available.

I then "fabricated" my own, a 4 hole 1 3/4" spaced hub for the later 3/4" Big Block shaft. This was on a 1967 water pump on a L71 435hp that included the larger 3/4" shaft. The BB pump date code and part# is difficult to see, but if the hub is a 8 hole it can often alarm the curious. The rebuilt original dated pump came to me from a West Coast water pump rebuilder but it had the 8-hole universal hub on the 3/4" shaft. I liked the idea of the improved 3/4" shafts for strength, albeit not originally used.

The hub can be seen by using a mirror at the back side of the pulley if judged. So we decided to use the 4 hole hub rather than rebuilding the pump and replace the bearing/shaft assembly with the less robust 5/8" shaft.

I lathe bored the ID of a new 4 hole hub with the 5/8" ID to the correct spec for the 3/4" shaft size and pressed it onto the shaft. That pump has been on the car for 6 years with many thousands of miles and has performed flawlessly.

Below you can also see the 3/4" shaft with the 5/8" pilot as mentioned for the pulley and fan clutch. I forgot I had these photos and your post prompted me to look for them.

Apologies for digressing somewhat from the small block discussion, but some information may be generally applicable.

Rich

Rich-------


There's something I can't figure out here. I'm not aware of any big block waterpump that ever used a 5/8" shaft. As far as I know, 1965-70 used a 3/4" shaft with a 5/8" pilot. 1971-74 used a 3/4" shaft with full 3/4" pilot.

[Richard M.]

Re: Small Block Water Pump Hubs

Rich-------


There's something I can't figure out here. I'm not aware of any big block waterpump that ever used a 5/8" shaft. As far as I know, 1965-70 used a 3/4" shaft with a 5/8" pilot. 1971-74 used a 3/4" shaft with full 3/4" pilot.

Joe, Sorry, I confused things when I said for the "later" 3/4" BB shaft. The bearing shaft was 3/4" as all BB's used. I'll edit my post....

The pump above had a 3/4" shaft inside the bearing, then up part way, then stepped to a 5/8" pilot. But I am a bit confused about that shaft. I'm thinking it may have been a special bearing/shaft assembly that they used in the rebuild, maybe a non-Corvette application. Photo 2 above shows the 3/4" shaft protruding from the pump, but continues towards the hub, then stepped to 5/8".

I see the 1965 to 1970 looks like below, with a 3/4" shaft inside the bearing, then as the shaft exits the bearing it is 5/8" for it entire length, for both the hub and the impeller. I understand all impellers used a 5/8" shaft. For reference, as all kits desribe, the grooved end of the bearing(or on some kits the grooved shaft) is the impeller end.


The 1971 to 1974 looks like this with the 5/8" impeller end and the hub end is completely 3/4" as you described. This kit also includes a 4 hole 2 1/8" spaced hub for the 3/4" shaft.


Here is a 1967 BB pump I recently worked on showing the correct 1965 to 1970 bearing assembly. It has a 3/4" internal bearing shaft but both exposed ends are 5/8".




Thank you Joe. I always enjoyed learning from you. You taught me more today.

Rich

[Joe L.]

Re: Small Block Water Pump Hubs

Rich------


Yes, I learned something here, myself. I always thought that the 1965-70 big block pumps used a 3/4" shaft through the hub but with a 5/8" pilot shaft outboard of the hub. However, that belief is incorrect. I just inspected an NOS GM #3876173 pump I have. This is the 1965-68 big block pump and the one I have was manufactured in November, 1966 [not for sale]. This pump has a 5/8" shaft outboard of the bearing but, obviously, with a 3/4" shaft through the bearing. I also have an NOS GM #3957982, the 1969-70 pump. I did not look at it but I expect it's the same.

This was a very dumb thing for GM to do but it probably simplified the assembly of the pumps.

[Richard M.]

Re: Small Block Water Pump Hubs

Joe, I agree that the 3/4" shaft, turned down to 5/8" for the hub and pulley/fan clutch pilot for the big block engines was very odd. The 5/8" shaft just doesn't make sense with all of that robust BB engine power. As you pointed out they obviously fixed that mistake in 1971 and beyond.

Rich