John Veninger

Thanks for all the good wishes everyone.
Being "pushed off" a bit is better than a 13/13 situation! Guess the #2 guy knew he couldn't pass me once we hit the straight

Having a group of 928'ers at the track made it easier to handle the situation, especially getting it on the trailer since I forgot the winch!
Dinner that evening was very enjoyable.

Wouldn't be a winter in the North East without me firing up the garage heater and pulling a 928 motor!

Head gaskets on order, intake valves to be ordered once I know the amount needed. Then send them off to the head guy for another valve job. Should be a bit "cheaper" (like anything for a 928 or racing is cheap!) this time around since I won't need valve seats installed and hopefully the guides are OK.

Bill Ball

Well, at least it happened at the end of the race season. Good luck with the rebuild, John!

Dennis K

Congrats John on breaking stuff in new and inventive ways!

Seriously though, I feel your pain. Those pics are gutwrenching. I hope the damage is as minimal as possible and the motor goes back together quickly.

SwayBar

Black Sea RD

John,

Very sorry to hear about the water pump failure! I wish you a speedy recovery and hope to see you at the Sebring races this coming year.

Way to go Mark A. with the n/c for the needed valves!

Wondering if the water pump shaft endures greater than normal forces with a stroker motor?

Best wishes,
Constantine

Mike Frye

I don't know about anyone else, but seeing this failure up close scared the he!! out of me. I would never have imagined that in an otherwise healthy motor with free-flowing WP shaft (which we assume it was, since it turned very easily by hand immediately afterward, while still VERY hot) there would be enough friction or resistence or something to cause this thing to somehow spin off the shaft.

I'm trying to wrap my mind around the cause of this thing because although the thing was only pressed on, I still can't imagine how much force it would have had to deal with. I think the RPMs are the same, and the tension is the same in a stroker so I don't see what that would have to do with it.

Anyone got any ideas about the real cause of this? Am I the only one that isn't able to picture this type of failure without some other cause?

Does the fact that it's a stroker cause more heat or more restriction to the water passages? Does the WP have any more work to do in a stroker engine?

69gaugeman

Pressing on a pulley is a very reliable way of assembly if done CORECTLY. All the wheels on all the locomotives are just pressed on! There has never been a case of a locomotive wheel falling off.

Having said that maybe the rebuilders need better equipment when assembling these things.

Being in the automotive industry, I see many pressed assembly's. They accurately measure the bore and the shaft and control the amount of press very carefully. Then during the press they use a recording force meter to record the pattern of force to insure they have a good press.

The amount of forces on the boundary of this assembly is relatively small in relation to the surface area. It only spins the impeller of the pump.

a4sfed928

My guess is the pump rebuilder reused the original pulley.

John Veninger

RACING put more stress on everything. The stroker itself shouldn't be any different in terms of the water pump to T-belt relationship.

Think it was a defective that showed up by track use. Bet it would have lasted years without an issue on a street motor.

JPTL

"My guess is the pump rebuilder reused the original pulley."
That's what I was wondering...if the shafts and/or the pulleys aren't replaced with new when rebuilt, I would think that the third(?) time around for a shaft/pulley to be pressed on & off on a rebuilt unit would start showing some fatigue & more slop.
You've got to wonder whether the rebuilders go to the extremes of quality control that Rob mentions.
Witnessing John's pump failure and thinking about how this really shouldn't happen, makes me want to take my original pump w/45k on it to a high end rebuilder & keep it for myself instead of turning it in for a core refund.

a4sfed928

I think the Stroker would put more stress on the pump if your pump had a metal impeller. The rotational speed impulses would be larger for a stroker motor and with the increased mass of a metal impeller it would place more stress on the frictional joint of the pulley. My .02

mark kibort

There are much higher increased forces on the pulley when running an engine to 6000rpm vs street driving. in fact, those force to spin the impeller through the water go up by the square of the pulley speed. the load on the impeller shaft might be as high as 1 -2hp, maybe a lot more! The inertial effects, in spinning the metal vs plastic impeller is relatively a very small factor. It can be roughly calculated by the weight and diameter of the impeller. the acceleration rates for throttle blips, (if you do that) are relatively slow so the forces on the pulley and the impeller wouldn be that great, but still a factor. All added up together, there are significant forces acting on the shaft, coupled with it being exposed to constant temperature change. This is a the reason that we have all seen impellers work their way off and now, JV's pulley work its way off.


Mk

Z

Just because it's a stroker motor, no. If there's an increase in engine power, yes. If the cams are bigger, yes. If the valve springs are stiffer, yes. If the valves are larger and heavier, yes. If the engine RPMs are higher, yes.

blown 87

I have seen it happen like that one time before, but not on a Porsche pump.

928SS

that stinks... I hate DNF's more than getting beat. I think. sometimes. kinda.

had that happen on my RV once w/a built mopar 440. wasn't a big deal cause we had a fridge full of beer.