Hey, I got a crazy idea. Messing around with these rear wheels I see that the cush drive pins, the ones threaded into the sprocket carrier, are heavy steel. I'm wondering if these could be made in aluminum, and not fail? They look pretty ordinary to me right now.
Cush Drive Pins
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Yeah! I agree. These things are way overkill I think for our bikes. There are six of these pins, and I seriously doubt the engine can produce enough torque to shear all of them off, even if they were aluminum. I'm pretty sure that shear is the major stress on those pins and not bending, since the sprocket carrier is held tightly to the wheel by the axle nut(s). Most shock loading is taken up by the cush drive so why not make these pins lighter?
Also, given that the cush drive is the same for a wide variety of bikes with different engine outputs tends to make me believe that this thing is way overkill. If it was really engineered to the nth degree, the cush drive would be specific to the engine displacement and/or power output.
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same here, i wouldn't do it, too much risk for too little gain,
i am likely to take no risks at all.
:think:
The relatively new 7068 grade of aluminum looks good, even better than titanium:
http://www.tpoparts.com/articles/aluminumalloys.html
I sent an email to them asking them the same question about the pins.
I tend to believe that Ducati often used steel because it was cheap and available, rather than the best material. The axle spacer 22 for example, is unbelievably heavy steel... It's not a highly stressed part, so why the steel? Aluminum would be fine. It could be the same for the pins.
Why would the pins need to be any stronger than the metal they thread into or slip into? The pins themselves should bear no more stress than the carrier or the wheel, right? Both of those are aluminum, and not even the high tech stuff. I could see a higher wear rate as an issue, though.
Yeah, that's what I wonder. I talked to TPO Parts and they did not recommend it, though they said titanium would be fine. I think the issue is that aluminum has no fatigue limit. If continuously stressed and shocked, it will eventually fail no matter how big it is made.
My bright idea of the day is to just remove some of them and use bolts in place of the empty spots on the carrier. I don't think 6 pins are required, though I have not done the math and don't really know how to do it.
Ducati used ordinary steel for the front brake disc bolts, and they are not that big. People replace them with titanium of the same dimensions, so they are not stronger. So, I just wonder what's the big deal about these pins? Maybe experience over the decades has shown the need for them to be this way... I don't really know.
We stock titanium drive pins for BST wheels.
We used to make a titanium/urethane cush drive set up for the single sided set up. They worked great, were light and the urethane lasted forever. However they were almost $300/set. We made about 3 batches of 100 sets. When we went to make the 4th batch. Our cost went up to almost $300/set--so we stopped making them.
-M
That's really cool, thanks.
My machinist backed out of the project because he thought it would take too much effort to make these and therefore would cost too much. He also wouldn't guarantee that they wouldn't fail, even when made out of Ti. I have someone else in mind, and possibly another place as well. I did some looking around and ordinary CP grade Ti rod isn't very expensive, so the biggest expense should be the labor to make them.
PM sent with the data.
I'm still not convinced that aluminum is a bad choice for this part. People sell aluminum front axles and various nuts and bolts after all... The design is way overkill for a 900 SS engine anyway. My god, these things are almost as big as car lug nuts, and there are SIX of them! Most cars only have four lug nuts, and put as much as 100 hp through them and they don't have the benefit of a rubber cush drive. Not only that, but a car lug nut is subject to far more stress than these pins. I don't get it, this makes no sense.
I've seen steel ones get sheared off on high HP bikes--I would not go aluminum on the drive pins. That is all you have to transfer the power to the rear wheels.
I'll find out about the TI ones. I'm pretty sure they are out of production--but they might make us some if we order a large batch.
-M
I'll find out about the TI ones. I'm pretty sure they are out of production--but they might make us some if we order a large batch.
-M
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