1970 fan clutch.

[Joe L.]

Re: More Addendum since we are there

Terry-----

The fact that Corvette went to a 3/4" waterpump pilot shaft for 1971 has always intrigued and confounded me. No other Chevrolet application ever went to 3/4" pilot except some MD and HD trucks. I don't even know why they did. There's absolutely no functional or performance benefit to the 3/4" pilot. All it does is "de-standardize" fan clutches and waterpumps.

Most other Chevrolet small block applications went to 3/4" through-the-bearing shaft size in 1971 and also went to the larger 2-1/8" bolt circle pulley/fan clutch configuration. However, all the rest maintained the 5/8" pilot.

In addition, as far as big block water pump assemblies go, the ONLY significant change for 1971 was the change in the pilot size from 5/8" to 3/4". Were it not for that change, all 1965-74 Corvette big block waterpumps, regardless of casting number for the pump body, would be interchangeable.

[Mike G.]

Re: More Addendum since we are there

i have the original. it is dated february 1970. its older than most of the parts on my car. i have a june car. i saw another type on a 70 corvette and he said he thought it was correct. it had a smooth face. i did not see a date code on mine until i looked at it again of friday. i am pretty sure this is the original. it cleaned up nice.
thanks for the help.

[Chuck S.]

Re: More Addendum since we are there

We always increased shaft size outside of the bearing fit area as an attempt to prevent fatigue failures resulting from product induced unbalance and vibration.

That was AFTER we had tried the strongest steels we could find. I remember having a shaft made out of 17-4 PH stainless steel when the usual 4340 wasn't quite making the grade...stopped the failures. Of course, we only had to retrofit about six pumps...17-4 PH was cost effective in that case.