"326" Water Pump Shaft Failure

[Joe C.]

Re: "326" Water Pump Shaft Failure

back in the day we used 5/8" shaft water pumps on race engines and never had that type of failure. i wounder if it was a case if they use a 3/4" shaft bearing and grind the end of the shaft for a 5/8" pulley and they leave a stress riser by leaving a sharp edge at the intersection of the two different diameters

Clem, as I said above, that bearing is a F.A.G. bearing, Canadian made. I bought it and the seal, hub, impeller, back cover, bolts and gaskets from Howard Stewart, whom you may know as being one of the premier water pump rebuilders in the country. He does work for many of the NASCAR teams, is ethical, reputable, and one helluva' straight shooter. His prices are ridiculously low, and the quality of his work is unmatched.

Does Mr. Stewart stand behind his products and services? Although I rebuilt the pump using his parts, he had me ship the broken pump back to him. He will rebuild it for me himself this time.............no charge.

That bearing was not molested/modified in any way. I saw it, and I installed it into the pump housing. If there was any installation issue, then the fault would have been mine, not Mr. Stewart's.

I suspect that my belts were too tight, which would have set up cyclical bending stresses at the bearing "pinch point", which led to eventual failure. It may have been an imbalance in the fan/pulley/clutch (which was not apparent to me, as the entire assembly ran vibration free and with almost no run out), but, Howard Stewart indicated that a slight imbalance would not have led to failure. He could have blamed it on the fan/clutch/pulley, and taken the "heat" off of his parts, but he did not.

[Dick W.]

Re: "326" Water Pump Shaft Failure

Clem, as I said above, that bearing is a F.A.G. bearing, Canadian made. I bought it and the seal, hub, impeller, back cover, bolts and gaskets from Howard Stuart, whom you may know as being one of the premier water pump rebuilders in the country. He does work for many of the NASCAR teams, is ethical, reputable, and one helluva' straight shooter. His prices are ridiculously low, and the quality of his work in unmatched.

Does Mr. Stewart stand behind his products and services? Although I rebuilt the pump using his parts, he had me ship the broken pump back to him. He will rebuild it for me himself this time.............no charge.

That bearing was not molested/modified in any way. I saw it, and I installed it into the pump housing. If there was any installation issue, then the fault would have been mine, not Mr. Stewart's.

I suspect that my belts were too tight, which would have set up cyclical bending stresses at the bearing "pinch point", which led to eventual failure. It may have been an imbalance in the fan/pulley/clutch (which was not apparent to me, as the entire assembly ran vibration free and with almost no run out), but, Howard Stuart indicated that a slight imbalance would not have led to failure. He could have blamed it on the fan/clutch/pulley, and taken the "heat" off of his parts, but he did not.

What did you use to tighten the belts, a six foot pry bar?

[Joe C.]

Re: "326" Water Pump Shaft Failure

What did you use to tighten the belts, a six foot pry bar?

I had "thrown" a belt last year, and did not want to repeat the event. All of the pulleys are the "proper" deep groove type, and the belts are Quanta, cloth wrapped 3V reproductions. And, yes, in overcorrecting I probably made the belts too tight. I use a short (14") section of wooden broomstick, which I wedge between the alternator/pump/etc. Sometimes I use a short, 12" hammer handle for tight spots.

Actually, in lieu of all the fancy formulas and belt tensioning gauges to measure force at the center of the belt span, the most efficient way to set belt tension is: "just at the point that there is no slip when the drive is subjected to max horsepower". That is NOT engine horsepower, just in case you may misinterpret the quote. It is horsepower that the belt is subjected to in driving alternator, pump(s), etc when they are all under FULL LOAD.

What were you thinking ("the groove") when you put up post number 9, and then tried to "cover it" in number 13 by repeating what I had said earlier.
Now, you know that a "fillet" is a stress relief radius, as well as being a cut of meat or fish!

[Clem Z.]

Re: "326" Water Pump Shaft Failure

I had "thrown" a belt last year, and did not want to repeat the event. All of the pulleys are the "proper" deep groove type, and the belts are Quanta, cloth wrapped 3V reproductions. And, yes, in overcorrecting I probably made the belts too tight. I use a short (14") section of wooden broomstick, which I wedge between the alternator/pump/etc. Sometimes I use a short, 12" hammer handle for tight spots.

Actually, in lieu of all the fancy formulas and belt tensioning gauges to measure force at the center of the belt span, the most efficient way to set belt tension is: "just at the point that there is no slip when the drive is subjected to max horsepower". That is NOT engine horsepower, just in case you may misinterpret the quote. It is horsepower that the belt is subjected to in driving alternator, pump(s), etc when they are all under FULL LOAD.

What were you thinking ("the groove") when you put up post number 9, and then tried to "cover it" in number 13 by repeating what I had said earlier.
Now, you know that a "fillet" is a stress relief radius, as well as being a cut of meat or fish!

belts usually come off of the alt pulley so we installed a belt guard on the pulley. look at your riding mower deck to see what i mean about the belt guard

[Joe C.]

Re: "326" Water Pump Shaft Failure

belts usually come off of the alt pulley so we installed a belt guard on the pulley. look at your riding mower deck to see what i mean about the belt guard

Thanks Clem.
I'll look into it.
I want to keep this motor as "stock" looking as possible as I'll be in F.A.S.T. class.

[Clem Z.]

Re: "326" Water Pump Shaft Failure

Thanks Clem.
I'll look into it.
I want to keep this motor as "stock" looking as possible as I'll be in F.A.S.T. class.

since it looks like you are drag racing i would put on the belt guard and run the belt loose so you get slippage and get some free HP by not turning the water pump and alt at high RPMs.. when we ran the flying mile at daytona beach back in the 50s we would cut the fan belt so it would fly off during the run. NASCAR caught on and would check at the end of the run to see if the belt was on and if not they would disqualify you

[Joe C.]

Re: "326" Water Pump Shaft Failure

since it looks like you are drag racing i would put on the belt guard and run the belt loose so you get slippage and get some free HP by not turning the water pump and alt at high RPMs.. when we ran the flying mile at daytona beach back in the 50s we would cut the fan belt so it would fly off during the run. NASCAR caught on and would check at the end of the run to see if the belt was on and if not they would disqualify you

Clem, you know all the tricks.
When I do a burnout to clean/warm the tires, wouldn't the same thing happen to a loose belt? It would clean up nicely and slip and burn up real good, too!
Wonder if the squeal would be noticed above the roar of open headers?

[Clem Z.]

Re: "326" Water Pump Shaft Failure

Clem, you know all the tricks.
When I do a burnout to clean/warm the tires, wouldn't the same thing happen to a loose belt? It would clean up nicely and slip and burn up real good, too!
Wonder if the squeal would be noticed above the roar of open headers?

the "belt guard" will keep it on the pulleys like it does on your lawn mower when you have the blades disengaged and the belt is loose

[Gerard F.]

Re: "326" Water Pump Shaft Failure

Joe,

You may have not passed the redline for your engine, but you did for your water pump. Looks like a torque failure. I'll bet the torque stress on the water pump shaft gets expodential above 5000 rpm.

But wadda I know, I'm only a civil.

Maybe try a larger water pump pulley (if there is such a thing), or a 3/4" shaft water pump, if you are going to do 7500 rpm on a 65 327 engine.

[Patrick H.]

Re: "326" Water Pump Shaft Failure

Joe,

You may have not passed the redline for your engine, but you did for your water pump. Looks like a torque failure. I'll bet the torque stress on the water pump shaft gets expodential above 5000 rpm.

But wadda I know, I'm only a civil.

Maybe try a larger water pump pulley (if there is such a thing), or a 3/4" shaft water pump, if you are going to do 7500 rpm on a 65 327 engine.

You could probably have a custom shaft made if you knew anyone with a CNC machine. Or, have the next one magnafluxed before installation.

Just thinking out loud...

[Clem Z.]

Re: "326" Water Pump Shaft Failure

if he is turning 8 grand i would remove that clutch fan because that is a lot of unsupported weight hanging out front to be spinning that fast. i know in theory they are not supposed to be turning at speed but i don't buy that. like i posted before we never ran the clutch fan where doing and type of track days. if we used a fan we used a flex fan.

[Joe C.]

Re: "326" Water Pump Shaft Failure

Joe,

You may have not passed the redline for your engine, but you did for your water pump. Looks like a torque failure. I'll bet the torque stress on the water pump shaft gets expodential above 5000 rpm.

But wadda I know, I'm only a civil.

Maybe try a larger water pump pulley (if there is such a thing), or a 3/4" shaft water pump, if you are going to do 7500 rpm on a 65 327 engine.

"Expodential"!

It must be that hard water I used to cut the Prestone with.

"Under-driving" the pump would work. But "how do it know"?

[Joe C.]

Re: "326" Water Pump Shaft Failure

if he is turning 8 grand i would remove that clutch fan because that is a lot of unsupported weight hanging out front to be spinning that fast. i know in theory they are not supposed to be turning at speed but i don't buy that. like i posted before we never ran the clutch fan where doing and type of track days. if we used a fan we used a flex fan.

Clutch is in "slip mode", or only partially engaged even on the hottest of days.

My temp gauge, which has been calibrated to read very accurately in midrange, or, from about 150 - 190 degrees Fahrenheit, is basically steady at 170 degrees at all times on days where the temp is anywhere above about 80 degrees. The hottest day so far has been close to 100, and the temp does not move. On cooler mornings of 60 - 80 degrees, the temp drops slightly, to about 160-165. The fan noise is "inaudible". I have never heard the fan howling with frenetic activity. The thermostat is a 160 degree unit, whose operation I have checked on the stove.

[Clem Z.]

Re: "326" Water Pump Shaft Failure

Clutch is in "slip mode", or only partially engaged even on the hottest of days.

My temp gauge, which has been calibrated to read very accurately in midrange, or, from about 150 - 190 degrees Fahrenheit, is basically steady at 170 degrees at all times on days where the temp is anywhere above about 80 degrees. The hottest day so far has been close to 100, and the temp does not move. On cooler mornings of 60 - 80 degrees, the temp drops slightly, to about 160-165. The fan noise is "inaudible". I have never heard the fan howling with frenetic activity. The thermostat is a 160 degree unit, whose operation I have checked on the stove.

GM went to a 3/4" diameter shaft for some reason and you may have found the reason. just for giggles weigh the fan and clutch to see how much unsupported weight you have hanging on the end of the 5/8" diameter shaft

[Joe C.]

Re: "326" Water Pump Shaft Failure

GM went to a 3/4" diameter shaft for some reason and you may have found the reason. just for giggles weigh the fan and clutch to see how much unsupported weight you have hanging on the end of the 5/8" diameter shaft

I respectfully disagree with you about your theory of unsupported weight. If the issue were pure cantilever stress from unsupported weight, then the fan/pulley/clutch assembly would have to weigh on the order of hundreds of pounds in order to bend or break a 5/8" diameter piece of hardened round stock. A very unlikely instance is where larger inertial mass would strain the shaft only when a very heavy assembly is either started or stopped abruptly. This requires very high acceleration values, and does not happen if the clutch is operating properly.

The problem(s) arise when the rotating mass is spun. Any unevenness in the distribution of that weight will cause stresses on the shaft along both the thrust and the radial axes. The forces/stresses produced will increase (probably as the square) of the imbalance point's radial velocity. When the material's modulus of elasticity is exceeded, then those stresses will remain as strains (deformations). You can see that the bending moment on the shaft at any time is proportional to (probably) the square of fan speed, weight value of the imbalance, and radial distance of that imbalance outward from the fan's center .

I don't have any of my college textbooks handy, so I take liberty in parenthesizing the word "probably" in a couple places, but you get the idea. If a practicing engineer with a better memory than mine cares to do the mathematical analysis, then that would be a very interesting exercise.