68 MO 302 water pump?

[jonboy1216]

an april 16 built MO 302 waht water pump should be on the thing?  i have been told that a 3859326 is correct .but i was on lucas restorations web site and they had pics of a june  68 rs z28 tore done from top to bottom and the pump that was on that car was 3839175 .any ideas what the difference is?

[1968 Z28]

Yeah that is a #175 water pump that was removed from the engine and if you look closely you will notice that it has a 3/4" outlet on top of the pump with a 3/4" to 1/2" reducer and then the 1/2" elbow on top of that.  Also if you look at the date code of the water pump, it does not line up with the date of the engine manufacture.....I would say that it had been probably installed in the past to replace a faulty original. 

If you look at the completed engine on album #3 you will notice that the 1/2" elbow is screwed directly into the pump indicating it now has a pump with the 1/2" outlet.  That 1/2" outlet is what the #326 pump has.  I would say that for sure they had now changed the water pump over to a correct dated one.

Just my observation......

[JohnZ]

The 326 pump was produced in two versions from the same raw casting - one version, for trucks, had a 3/4" hole for the large bypass fitting; the other version, for Corvette and passenger cars, had a 1/2" hole for the smaller bypass fitting.

When 326 pumps with the small bypass fitting hole find their way to a commercial rebuilder, almost all of them get enlarged and re-tapped to the 3/4" bypass fitting hole, since the primary demand for them is for trucks, not Camaros and Corvettes; that's why you see so many of them with a reducer bushing to accept the 1/2" bypass fitting. In NCRS Corvette judging, presence of a reducer bushing gets a deduction, as the original factory 326 pump used in production had the 1/2" hole for the fitting.

[1968RSZ28]

The 326 pump was produced in two versions from the same raw casting - one version, for trucks, had a 3/4" hole for the large bypass fitting; the other version, for Corvette and passenger cars, had a 1/2" hole for the smaller bypass fitting.

When 326 pumps with the small bypass fitting hole find their way to a commercial rebuilder, almost all of them get enlarged and re-tapped to the 3/4" bypass fitting hole, since the primary demand for them is for trucks, not Camaros and Corvettes; that's why you see so many of them with a reducer bushing to accept the 1/2" bypass fitting. In NCRS Corvette judging, presence of a reducer bushing gets a deduction, as the original factory 326 pump used in production had the 1/2" hole for the fitting.

John -

Jerry MacNeish's "The Definitive 1967-1968 Camaro Z/28 Fact Book" states that the water pump installed on all 1967 and 1968 Z/28 engines had two slightly different designs; one with a 1/2" NPT bybass hole and one with a 3/4" NPT bypass hole.  What may be correct for a Corvette, might not be for a Camaro.

 

Paul

[1968 Z28]

The 326 pump was produced in two versions from the same raw casting - one version, for trucks, had a 3/4" hole for the large bypass fitting; the other version, for Corvette and passenger cars, had a 1/2" hole for the smaller bypass fitting.

When 326 pumps with the small bypass fitting hole find their way to a commercial rebuilder, almost all of them get enlarged and re-tapped to the 3/4" bypass fitting hole, since the primary demand for them is for trucks, not Camaros and Corvettes; that's why you see so many of them with a reducer bushing to accept the 1/2" bypass fitting. In NCRS Corvette judging, presence of a reducer bushing gets a deduction, as the original factory 326 pump used in production had the 1/2" hole for the fitting.

John -

Jerry MacNeish's "The Definitive 1967-1968 Camaro Z/28 Fact Book" states that the water pump installed on all 1967 and 1968 Z/28 engines had two slightly different designs; one with a 1/2" NPT bybass hole and one with a 3/4" NPT bypass hole.  What may be correct for a Corvette, might not be for a Camaro.

 

Paul

I know my original 326 water pump had the 1/2" outlet because when it went out back around the 70's, I replaced it with one with a different number, different date, and one with the 3/4" outlet.  I remember having to use the reducer for the elbow.  Unfortunately, I didn't keep my original but as of lately I have bought a 326 with a 1/2" outlet and matching date code for my engine.

But it sure cost a lot more now than the replacement back in the 70's.....LOL

[jonboy1216]

thanks guys i will get the 1/2 326 pump for my car

[john302]

Call Bill Mock for the correct pump,he is the best.

[JohnZ]

Call Bill Mock for the correct pump,he is the best.

You can reach Bill at (918) 333-0748, or mockauto@aol.com.