red motor water pump

[jack_fc]

Gday all
I'm trying to fix an over-heating problem on my (modified) "3.3" red motor (last of the reds; out of VC commie?? engine no. prefix VL)
I have been told that some aftermarket water pumps have very poor tolerances between impellor and body, and consequently can suffer some cavitation and reduced water flow. A well-respected man in the industry backed this up - specifically mentioned "GMB" brand as being prone to this. I currently have this brand pump fitted. It was suggested that a genuine water pump would be the go. Local GMH dealer says they come up on his computor as "obsolete".
Repco can supply "Silverline" brand at $29; Bursons "GMB" at $41 (same as currently fitted). It also appears there are 'short shaft' and and 'long shaft' pumps available. Which one should be fitted to a 3.3 red?
Anyone had any experience with these brands? Are there any other brands available? Are genuine pumps still available somewhere?
It has also been suggested that the impellor/body tolerance can be reduced by pressing the impellor further onto the shaft - anyone had a crack at this? If so, how was it done and what clearance should be left?
Of course, the problem could also be caused by other factors, but I seriuosly doubt its the radiator (aluminium triple flow - similar to ADC type; fairly new), could be insufficient air flow (Davies Craig 14" 1400 cfm - about 4 years old; no engine fan - no room). Anyone got an opinion on whether 1400 cfm is sufficient for a modified red?
Have finally sourced a new Milodon hi-flow thermostat n will fit soon as it arrives, but asking these questions in case this doesnt solve the problem.
All feedback gratefully accepted!!
cheers jack

[FC427]

Jack I have had no problems closing the impeller gap with cracking . The other water pump is longer and has a heavier bearing to support the large and heavy clutch fan they use on Commodores, you don't run a fan so can't see a need to change. As for the 1400 cfm I doubt this is enough for a hot motor I also run an aluminium radiator and 16'' 2800 cfm fan. ......FC427......... 

[jack_fc]

thanks FC427. Did you close up the gap by using hammer and tube spanner (or similar)? Any idea on how much gap you left? Was wondering what effect operating heat may have on the gap - shouldnt be a problem; pump housing is cast alloy, n I'm assuming this would expand more than the steel impellor.
I'm thinking youre right in doubting that 1400 cfm is enough for a hot red, but getting a higher airflow fan in there may be a problem. ICE brand 14" fans are rated at 2000 cfm, but seem to be about 10 - 12 mm thicker than the DC fans; I dont think there is a spare 10 mm in there! Could look at mounting fan in front of radiator, but bugger-all room there too.
Anyone else want to throw their 2 cents worth in??
thanks jack

[FC427]

Jack i put it in my press to close it up a bit went from 18thou to 12 thou and I have an ICE 16'' fan mounted in front of the radiator and it does fit. As for expansion 100 c + or - 20c it would not expand very much at all I would think . It would be easy to measure it cold and then boil it in water on the BBQ and measure it again and then there would be no guessing ......FC427......

[jack_fc]

FC427, ta mate; that gives me something to aim at (12 thou), pity I dont have a press - will try hammer etc and feeler gauge (and patience). My radiator is mounted forward of where it would be on a stocky - already almost impossible to replace fan belt; only 6-8 mm between w/pump pulley and thermo fan. But your comment has made me think about moving the thermo to the front AFTER moving the radiator back a bit. This would allow me to fit a 16 (instead of 14') fan AND allow sufficient clearance for belt removal.
The current fan is 14" Davies Craig (1400 cfm?). Replacing it with a 16" ICE fan would in theory double the airflow. Anyone got any thoughts on front versus rear mounting of thermo fans?
cheers n thanks
jack

[Ed]

hey jack,

sent a reply previously but it didnt work.

I tried shrouding a rear mount thermo but it didnt work at speed.  Also sounds like you have probs with space.

Currently configured with twin mounted 12" fans on a removable frame, and works well with the other mods.

In my experience front mounted fans have always performed better and bigger the better.

Nice to meet at the Nats, like your ride.


Cheers
Ed

[jack_fc]

thanks Ed. Currently investigating if/how I can move radiator back enough to fit thermo fan in front without inflicting too much (aesthetic) damage - wont be easy, but what is on these cars? 
After sitting down and having a good think, I've convinced myself that front mounted has gotta be better; fan motor in cooler air, working in higher air pressure rather than lower, etc. Just need to make sufficient room...
Great to meet at the Nats, your car has inspired me to maybe make mine a bit more 'out there', but I'm a conservative old bastard and have tended towards the 'understated' look - maybe its time I got dragged into the nineties!
cheers jack