Differences in ohc 6 water pumps?
 

Looking for a replacement water pump for my 1969 tempest. I see brand new ones for sale for 66-67's. So what is the differences?

Length of the shaft. I have a NOS 69 short pump available. The pulleys wont align if you try to use a 66 thru 68 long shaft pump.

I also have a couple reman '69 pumps laying around if anyone needs them.

WP 66-68 Vs 69
 

As mentioned the '69 WP has a short shaft unlike the long shaft on the '66-'68 pumps.
Also '69 no longer used a By-pass at the radiator hose neck, it was now incorporated into the casting.

Can the 66-68 be drilled out for a bypass and a shorter shaft installed or maybe cut off to make a 69? Looks like some of the 69 pumps have the 66-68 tap for the bypass and maybe someone made a 69.

Either can be done, I drilled a bypass hole in a 68 block once to use a 69 water pump. It would also have been possible to drill & tap a 69 water pump to use the external bypass hose of the 66-68 engines.

Funny that it took the engineers so long to figure that out...But maybe the bypass hose had advantages??

IMHO It would be far less effort the oe/correct rebuilt and/or rebuild it.

I just had two done, not cheap but they're not being pushed over the counter anymore.
Rebuild kits should still be available if you are able.

I was told it was a cost cutting move, Pontiac was being pressured to drop the OHC-6 and purchase Chevy I-6's. Chevy was making the case they could provide the chevy 6 at a price lower than Pontiac could build the OHC-6 and Chevy could still make a profit. Pontiac made many small changes to the 69 OHC6 besides the water pump.

The Water pump change eliminated many parts besides the bypass hose, there was the thermostat spacer, 2 hose clamps, and the fitting for the bypass hose on the water pump. The machining changes to block line consisted of drilling 1 more hole in the block for the internal bypass.

Besides the water pump they also

(1) replaced the cast aluminum rear upper timing belt cover with a stamped steel one. This also required the larger fiberglass upper cover to be remade with 2 bulges to screw the new cover onto.
(2) Replaced the upper timing belt cover mounting bracket that bolts to the front of the block and held the cover with 3 Mounting screws. With 2 Threaded stand offs that thread into the smae 2 holes in the block that the bracket did. And reduced the front upper cover mounting screw number from 3 to 2.

They also made some minor changes I forget at the moment. These changes required the modification of the following parts

Timing Belt front cover
Water Pump Pulleys
adding a flange on the timing cover to accept the thermostat without the spacer.
Replacement of the water pump gasket with a new design to use the internal bypass hole. It would also replace the 66-68 design as it would work with either water pump.

The changes eliminated about 10 parts from each engine made. The change in water pump shaft length was to prevent the installation of the incorrect water pump by mistake.

From a conversation with Fred Simmonds years ago.
The water

No dought the bean counters were part of the changes.

I'm unaware of any Cam housings not having the step for the Thermostat,
thus why the question of placement with the bypass seems to come up.
Compounded by the misguiding parts book image.

Didn't know that the pump change was to prevent older pump installs. Good stuff.

Jeff I used to have a few very early 66 Cam covers that did not have the step for the thermostat. But you are correct all 6 of the ones I currently have all have it.