Water Pump Rebuild Question

[Ed McGettigan]

I am replacing my water pump in my 64 327/300 since I am detailing the engine and have everything apart I figured I may as well since I'm not sure how long the current one has been in there. I was reading some archived threads about hi flow vs stock water pumps and someone recommended rebuilding the current pump but having a "ball-roller" bearing installed. Can someone explain to me the benefit of using a ball-roller bearing?

Thanks...

[Joe L.]

Re: Water Pump Rebuild Question

Ed-----

Original bearing/shaft assemblies used on 1955-1970 Corvette small block water pumps used 2 rows of ball bearings to support the shaft. The shaft OD on these assemblies was 5/8".

1971-82 Corvette small blocks and all Corvette big blocks used a larger bearing/shaft assembly. For these assemblies, the shaft OD was 3/4", although the impeller end of the shaft was turned down to 5/8" (the pilot end of the shaft was also turned down to 5/8" for 65-70 big blocks).

I think that the larger bearing/shaft size described above was a ball-roller design, in which the shaft was supported by 1 row of roller bearings and 1 row of ball bearings. This design creates a much stronger bearing for increased pump durability and support of the larger fan systems which came into use in the early 70s.

I think that the ball-roller design requires the use of the larger bearing/shaft assemblies which are not interchangeable with the 1955-70 small block units. To my knowledge, a ball-roller assembly is not available for the 55-70 style pump. However, if it is I'd like to know the manufacturer and the part number for the bearing/shaft assembly for 55-70 Corvette pumps. I am not aware that either FAG, SKF or Toyo, the primary manufacturers of waterpump bearing/shaft assemblies makes a ball-roller unit for the 55-70 style pumps, but they may now.

[Duke W.]

Re: Water Pump Rebuild Question

Ball-ball and ball-roller bearings are available in BOTH SAE 5/8" and 3/4" sizes. The early SB waterpumps were originally equipped with 5/8" ball-ball bearings, and replacing this with a ball-roller will improve bearing life because it has greater load capacity. I recommend the ball-roller bearing for all water pump rebuilds - both those with 5/8" and 3/4" SAE bearing sizes.

Can't say for sure how much more life it will have, but the 5/8" ball-ball bearings are living on borrowed time at 50K miles.

I would NOT recommend a "high flow" impeller. If the original is in good shape, just reuse it. If you don't have a water pump rebuilder locally or that you trust you can contact Superior Pump in Hawthorne, CA, 310-676-4995. Ask for Sharon.

Duke

[Jack H.]

Re: Water Pump Rebuild Question

Water pump rebuild kits are also listed in several of the Corvette parts catalogs (Chicago Corvette/Corvette Central) for the do-it-yourself folks using their copies of Corvette Shop Manual/Chassis Service Manual who have hydraulic press and media blast cabinet facilities....

[Roy Braatz]

Re: Water Pump Rebuild Question

Duke is rigt stay away from the high flow , keep the original so that the water wont pass through the Rad. to fast.

[Michael W.]

Hey Roy-

If the water passes through the radiator so fast that it can't 'lose' the heat, wouldn't it also pass through the block too quickly to absorb it?

[Doug Flaten]

Re: Hey Roy-

I guess my thermodynamics and heat exchanger books are all wrong. Sounds like we need to slow down the fan spped too, because we may not be giving the air enough time to pick up all the heat. How does this theory hold for air cooled engines? The simple question is when is an air cooled engine cooler,... high air flow or some slower "optimum" air speed?

[Roy Braatz]

Re: Hey Mike

That's a big NOOOOOOOOOOOOOOO.

[Roy Braatz]

Re: Hey Doug

We are talking WATER right???????????

[Michael W.]

Re: Hey Roy

Thanks for your outstanding technical explanation. I am in awe.

[Doug Flaten]

Return of the Heat Transfer Debates

It makes no difference if you are talking water or air or which side of the radiator you are talking about. As the water transfers heat to the air via the radiator tubes and fins, the difference in temperature between the water and the air side of the radiator is reduced. This temperature difference is the driving force in heat transfer similar to the voltage potential that provides the driving force in an electric circuit. Reduction of the temperature differential results in a reduction of heat transfer. Ideally, you would want to maintain a high tube and fin temperature so that more heat is driven out into the air. The coolant flow rate transports the heat from the engine to the radiator maintaining a high radiator temperature. An air cooled engine just simplifies things. I don't think anyone would argue that higher air flow will cool an air cooled engine better. In this case, the cooling fins are cooled down more with greater air flow. This creates a larger temperature differential (driving force) between the base of the fin and the tip of the fin, thereby the rate of heat transfer though the fin.

The velocity of water flowing through a tube is higher in the center of the pipe than it is along the walls of the pipe. The static film along the pipe walls acts as somewhat of an insulation layer between the rest of the fluid and the pipe wall. Within reasonable limits, increased flow rate increases the flow velocity along the walls of the pipe and reduces the boundary film along the walls. The reduced film increases the ability of the fluid to tranfer heat into the tube.

I am not saying that you need more air or water flow to fix a cooling problem. A clean and properly functioning stock cooling system will cool sufficiently. However, increased water or air flow will not worsen the problem as has been suggested in previous posts.

[Roy Braatz]

Ok Guys

Ok lets look at this is way, the engine is the heat source and radiator the cooler. G.M engineers surly thought through this thing and matched the water pump impeller to the radiator design and volume. Right? My past experience having had hot rods found that pushing the water faster through the radiator doesn't allow the water time to cool down. It returns to fast back to the heat source the engine which increases more heat and again is sent to the radiator which again hasn't time to cool the water. At idol the radiator may be able to keep up with the heat source but as your driving faster the water flow is faster and then here is your problem. In the old days pep boys sold a pack of large washers that replaced the thermostat , the washers had various holes sizes that you tried till you ether increased or decreased water flow to control temperature on your hot rod engine. Ok! now let me have it guys.

[Clem Z.]

Re: Ok Guys

when we raced BBC engines at high RPM(6000+) we had to remove every other fin from the stock water pump impeller to cut down on cavatation to get the engines to cool. i installed a pressure gauge in the water passage in the intake manifold next to the upper rad hose outlet and we saw the pressure drop to less then 5# at 6500 rpm and after the pump impeller change we saw over 30# of water pressure. you need the pressure to fill all the water cavities in the heads. also another thing i found was that rad hoses must be smooth inside to allow the water to flow because the hoses with built in renforcement that have a spiral surface to them also cause water flow problem. we also ran a restrictor instead of a thermostst and 5/8" to 3/4" worked the best as you need the restrictor help build the pressure in the block and heads. as you add HP to the system you also add more heat so if your engine made 250 HP and you build it to 350 HP you will need more rad.

[Doug Flaten]

OK Now We're Also Talking Pump Theory

Ok, now we are putting another element into the equation. You both have mentioned running the pumps at high rpm, likely exceeding their factory stock design parameters. The hot rod engine is making more horsepower and more heat. More heat puts it closer to the boiling point where cavitation will be a problem for a pump spinning at high rpm. Most water pumps, especially the stamped steel ones, are a bean-counter compromise at best. At high rpm, there is a locallized reduction in pressure on the suction side. If the coolant is near boiling point, the pressure drop is sufficient to cause the coolant to vaporize as it enters the pump. Gas/steam takes up more volume in the pump and is compressible, so pump output is reduced. In severe cases, the fins or vanes on the pump can be destroyed as the bubbles implode on the surface of the pump. The coolant flow rate is reduced because the pump is trying to pump vapor creating a low discharge pressure as noted by Clem. In Clem's case, he modified the pump, both reducing its required suction head and reducing its flow capacity. However, his modified pump of reduced flow capacity will circulate more water than a pump that is hardly pumping any water because it is cavitating. The restrictor plates were used to place back pressure on the pump, which reduces the flow through the pump. This in itself may have prevented the pump from cavitating, thereby allowing it to actually move more coolant than when it is cavitating and moving less coolant. Depending on the size of those thermostat restrictor orifices, some may even flow more than the stock thermostat. They would have different flow coefficients due to the geometry of the openning. Ribbed hoses will create higher friction losses which would reduce the amount of pressure available at the pump inlet, further compounding cavitation problem. In both examples, the pump is operating out of design parameters. There are aftermarket pumps available such as Stewart, that are designed to operate at higher rpm's and flowrates without cavitating. Running the system with a higher radiator cap pressure, may also eliminate cavitation problems by providing more positive suction pressure. A high flow pump is also going to provide higher discharge and system pressure. As you said Roy, the boys at GM knew what they were doing, and the stock components will function properly together. You start operating those components outside of the design parameters, and you may experience problems. Placing a 350 ci engine in an early Vette is likely to result in cooling problems. However, a properly designed high flow pump and possibly a fan that flows more air may allow you to get by with a good clean stock radiator.

[Clem Z.]

Re: OK Now We're Also Talking Pump Theory

i never got any farther than high school so all that theory goes way over my head but i did what i had to and by the good grace of god i stumbled on what worked.