Here is why not to use a cog belt on the street.....

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......
brokendrive1.jpg
brokendrive3.jpg
brokendrive2.jpg

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" :rolleyes:

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
 
How many miles on that coupler? Is that a solid coupler or was it the spring type? Looks like a solid one to me from the pic. Even if the couple flew apart, how can that damage the rotors that are attached to the gears and rotor plate? If the coupler was a weak point how was the keyway damaged?

I find it hard to believe that it's normal for everybody's SC belts to slip under 1-2 up shifts even with a very firm shift. Are you sure you just didn't have a worn coupler?

Also I don't like the fact that you are making a determination that a cogged belt wont work even though you are not using one. I wont take this information as gospel, but will take a note.


Skeptical

Jerry
 
very interesting

wondered about this for a while ...8lbs plus of spinning mass ...spinning @ 14,000 ...David Neibert case 20,000 + rpm ...then being told to decellerate all of a sudden ..with next the gear change ...that's got to hurt if the belt don't slip ..and I ask myself ...why not clutch ...the jack shaft..let it free wheel ...on shifts ..won't rob HP spooling up ..it has no choice but to make boost ..it's not a turbo ....dave
 
MercsSC said:
wondered about this for a while ...8lbs plus of spinning mass ...spinning @ 14,000 ...David Neibert case 20,000 + rpm ...then being told to decellerate all of a sudden ..with next the gear change ...that's got to hurt if the belt don't slip ..and I ask myself ...why not clutch ...the jack shaft..let it free wheel ...on shifts ..won't rob HP spooling up ..it has no choice but to make boost ..it's not a turbo ....dave

I don't really think there is a problem with sudden decelleration of the supercharger. Keep in mind it doesn't want to be spinning that fast and it takes between 65 and 125 HP off the crank to turn it. That same amount of HP is going to help slow it down until the bypass valve opens.

With an automatic transmission your foot stays on the floor and the boost is constant during upshifts, so the supercharger is constantly under a load.

David
 
Regardless of why the above happened a little bit of slip is built in and is good for an everyday driven car. If your purely track..Go for a cog...They hav eeven been experimenting with chain driven blowers..The ultimate in non slip...But in that case..you have 0 chance of slip...

10 rib is a happy compramise..If its slipping with that apparently its meant too (IMO)
 
How many miles on that coupler?
About 6k.
Is that a solid coupler or was it the spring type? Looks like a solid one to me from the pic.
Solid
Even if the couple flew apart, how can that damage the rotors that are attached to the gears and rotor plate?
The coupler most likely would not damage the rotors or gears, however once the pins back out of and tear up the drive, they can lock up the gears and start doing some real damge real quick. I was lucky that the metal pieces floating around the fluid didnt tear up more than just the bearings. If you saw what the fluid looked like when emptied before taking the snout off, you would cringe.
If the coupler was a weak point how was the keyway damaged?
Though the coupler was a weak point, it was not what started the chain of events, the drive did. As for the keyway being damaged, the inerta of the rotors trying to keep spinning with the engine trying to spin the other direction without the belt slipping to take up the slack makes the aluminum pulley keyway the next week link. In this instance, the pulley was material was stronger than the drive so the drive let go first. To continue running with no belt slippage would require me to go to a steel pulley and hope the key itself doesn't break.
I find it hard to believe that it's normal for everybody's SC belts to slip under 1-2 up shifts even with a very firm shift. Are you sure you just didn't have a worn coupler?
Well, they do and they have to for longevity reasons. If they never slipped, you would see a sudden boost spike during the shifts when the rotors start to overspeed for an instant. Think back to the "objects in motion tend to stay in motion" statement.
Also I don't like the fact that you are making a determination that a cogged belt wont work even though you are not using one. I wont take this information as gospel, but will take a note.
Like it or not, the purpose of running a cogged belt is to stop slippage. The system I ran did the same thing in a different way. Ever wonder why Coy said he had to change his cogged belt every 300 miles? Something has to give.


Paul
 
68COUGAR said:
What happened to the pics? All I see is 3 small boxes, with red X's in'em.

68COUGAR

They are working fine on my end. I just checked the server and it is up so it must be a problem you are having.

Paul
 
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