BT Motorsports
Registered User
On my way back to St Louis from Carlisle, I pulled over on the side of the highway to put air in a tire with a slow leak. Due to traffic speeds, I had to lay into it to merge back into traffic. Just moments after the 1-2 shift at around 6K RPM, the engine lost boost and nosed down. After immediately pulling over and inspecting the problem, my fear was confirmed, the blower drive spun out on the shaft. Here is what happened......
Here is an account of what occured causing this damage from someone (me) who it has been stated "is not qualified to discuss supercharger drive systems"
During the shift at high RPM, high load, the rotors want to keep acellerating and turning in the direction they already are while the engine is slowing down and trying to make them go the opposite direction. This shock is absorbed primarily by the coupler and drive hub/pins. What happened in this instance is the constant shock the drive hub saw during these conditions caused the pins to bend away from being perpendicular to the hub. While the pins bend very little, what actually happens is the aluminum hub gives a little each time allowing the pins to move. As the blower continues to be in service, the pins oblong the hole they are pressed into further and further. You can see in the pictures the hub allowed the pins to lean far enough over that they back out of the bore they were pressed into. This allowed them to back away from the coupler far enough to tear their way out of it. As this continues happening, the splines on the shaft which the hub is pressed onto begin to distort along with the aluminum hub bore itself. Eventually, the press fit of the hub on the shaft gives way entirely and spins freely fully disengaging the rotors. As you can see, I got lucky that I caught it immediately and removed the blower belt then proceding to drive over 700 miles naturally aspirated back to St Louis. The only damage is what is seen above. The rest of the blower was not hurt and the snout now has a new shaft, STEEL drive hub, bearings seal and coupler. The blower pulley keyway was also tore up a bit, however not enough to warrant replacement at this time.
For the record, I utilize the ESM 8/10 rib pulley and belt system which does allow some slippage to occur during the shifts as part of its design. In my particular instance, I increased tension on the crank to jack pulley to fully eliminate slippage from occuring during the shift and dearly paid the price. This is effect created the same characteristics as a cog setup except the belts did not break or take out any components under the hood or further damage the supercharger like a cog setup potentially could have. Granted, my situation is not typical of all others, however, it does demonstrate the drive's limitations and weakness. Next time you discount my opposition to the friction design of the whipple which sits in an anti friction oil bath to keep the rotors in time and turning, reflect on what can happen to the eaton design which is a positively located drive.
I have no one to blame but myself for this occurance, especially because I did not key the drive hub when I had the snout apart for a rebuild about 6 months ago. Had I done so and changed over to a steel drive hub, this would have been potentially avoided or seriously prolonged.
Paul
Here is an account of what occured causing this damage from someone (me) who it has been stated "is not qualified to discuss supercharger drive systems"
During the shift at high RPM, high load, the rotors want to keep acellerating and turning in the direction they already are while the engine is slowing down and trying to make them go the opposite direction. This shock is absorbed primarily by the coupler and drive hub/pins. What happened in this instance is the constant shock the drive hub saw during these conditions caused the pins to bend away from being perpendicular to the hub. While the pins bend very little, what actually happens is the aluminum hub gives a little each time allowing the pins to move. As the blower continues to be in service, the pins oblong the hole they are pressed into further and further. You can see in the pictures the hub allowed the pins to lean far enough over that they back out of the bore they were pressed into. This allowed them to back away from the coupler far enough to tear their way out of it. As this continues happening, the splines on the shaft which the hub is pressed onto begin to distort along with the aluminum hub bore itself. Eventually, the press fit of the hub on the shaft gives way entirely and spins freely fully disengaging the rotors. As you can see, I got lucky that I caught it immediately and removed the blower belt then proceding to drive over 700 miles naturally aspirated back to St Louis. The only damage is what is seen above. The rest of the blower was not hurt and the snout now has a new shaft, STEEL drive hub, bearings seal and coupler. The blower pulley keyway was also tore up a bit, however not enough to warrant replacement at this time.
For the record, I utilize the ESM 8/10 rib pulley and belt system which does allow some slippage to occur during the shifts as part of its design. In my particular instance, I increased tension on the crank to jack pulley to fully eliminate slippage from occuring during the shift and dearly paid the price. This is effect created the same characteristics as a cog setup except the belts did not break or take out any components under the hood or further damage the supercharger like a cog setup potentially could have. Granted, my situation is not typical of all others, however, it does demonstrate the drive's limitations and weakness. Next time you discount my opposition to the friction design of the whipple which sits in an anti friction oil bath to keep the rotors in time and turning, reflect on what can happen to the eaton design which is a positively located drive.
I have no one to blame but myself for this occurance, especially because I did not key the drive hub when I had the snout apart for a rebuild about 6 months ago. Had I done so and changed over to a steel drive hub, this would have been potentially avoided or seriously prolonged.
Paul