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Alaskavan
Guest
I think Zombie Builder ran into the same kind of problems using CVT's. He switched to a NuVinci.
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kerf
Guest
Yeah, I spent some time last night exchanging PMs with robotguy on GopedNation. The pocket bike CVT works great on a bicycle, except for the bad design and poor materials used in the transmission. At first I thought I had installed a bushing backward but now I realize that the bushing was a flat washer that was turned and drawn by the variator ramp plate, as the trans shifted. The variator shaft had a square shoulder that now is nicely rounded as the washer was pressed around it.
Was just down in the shop, viewing the prostrate corpse of my mistress. I think kerf is in mourning. I need to cover her up with a sheet, I can't look anymore.
Was just down in the shop, viewing the prostrate corpse of my mistress. I think kerf is in mourning. I need to cover her up with a sheet, I can't look anymore.
loquin
Well-Known Member
Kerf - do you think that if the flat washer was not as ductile, (maybe if it were heat treated/annealed,) that the variator plate would have stood up (as the forces wouldn't have been concentrated right at the shaft - they would have been spread out over the washer) ???
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kerf
Guest
The design flaw looks pretty bad. The outer variator pulley side, is the only part keyed to the shaft and that is only with a couple of flats cut into the end of the shaft. The material thickness of that pulley is less than 1/8" and that's not much to handle all the rotational torque. The variator itself and it's associated bushing are only keyed to the shaft by friction created by the nut on the end of the shaft. I believe, during operation, the bushing and variator slip and the spinning shaft, along with the variator pressure, drew the flat washer into a flanged bushing shape and cut away the soft steel shoulder on the shaft. I tried a heaver washer but it just cut into the shaft as well.
My idea was to use a spacer to bypass the soft shoulder and place the load directly on the inside bearing race. Robotguy, from GopedNation, feels the variator would damage the bearing, I don't know. From the factory, the variator forces were contained between the shaft nut and the shaft shoulder. Since the clutch drum hub (see pic) screws on the shaft and bottoms on the bearing race, I believe the forces would still be contained within the shaft and have little effect on the bearings.
My idea was to use a spacer to bypass the soft shoulder and place the load directly on the inside bearing race. Robotguy, from GopedNation, feels the variator would damage the bearing, I don't know. From the factory, the variator forces were contained between the shaft nut and the shaft shoulder. Since the clutch drum hub (see pic) screws on the shaft and bottoms on the bearing race, I believe the forces would still be contained within the shaft and have little effect on the bearings.
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loquin
Well-Known Member
K
kerf
Guest
When my bike was running with the CVT, it was great, I've never ridden anything as good. I've been trying to understand what happened, did I assemble something wrong, is this the life span I can expect, what?
God help me, kerf's just not very smart but eventually that little dim light will begin to faintly glow. I looked over the postmortem and the outer plate failure indicated that it had become loose on the shaft and allowed the keyed hole to wallow out. The evidence pointed to the shaft shoulder being rounded and the washer, behind the ramp plate, being deformed to the point it looked like it was made that way from the factory. I have made a schematic of the washer, as seen on edge, before and after deformation. The drawing isn't to scale but only for illustration purposes.
What became apparent was, there is no way the variator could have generated enough force to "forge" a flat washer into that shape. So how did it get that way? When the variator is in it's low range, the belt doesn't bottom out on the bushing, as does a Comet CVT but stays suspended between the sheaves. Before I switched the 63 tooth sprocket for the 72 tooth, I went hill climbing. I live at the bottom of a steep hill, that no bike of mine has ever climbed, except my 6HP, Comet driven mini trail and then with a great deal of strain. I just wanted to see if the spokes would hold under that much strain. What I believe happened was, under that much load, the belt was forced deeper into the variator but there was no room for it to go. Force built up until the weakest part failed. I still rode the bike several times before the symptoms began to show themselves.
As I type this, the MIG is warming up, I intend to bring my mistress back from the grave!
God help me, kerf's just not very smart but eventually that little dim light will begin to faintly glow. I looked over the postmortem and the outer plate failure indicated that it had become loose on the shaft and allowed the keyed hole to wallow out. The evidence pointed to the shaft shoulder being rounded and the washer, behind the ramp plate, being deformed to the point it looked like it was made that way from the factory. I have made a schematic of the washer, as seen on edge, before and after deformation. The drawing isn't to scale but only for illustration purposes.
What became apparent was, there is no way the variator could have generated enough force to "forge" a flat washer into that shape. So how did it get that way? When the variator is in it's low range, the belt doesn't bottom out on the bushing, as does a Comet CVT but stays suspended between the sheaves. Before I switched the 63 tooth sprocket for the 72 tooth, I went hill climbing. I live at the bottom of a steep hill, that no bike of mine has ever climbed, except my 6HP, Comet driven mini trail and then with a great deal of strain. I just wanted to see if the spokes would hold under that much strain. What I believe happened was, under that much load, the belt was forced deeper into the variator but there was no room for it to go. Force built up until the weakest part failed. I still rode the bike several times before the symptoms began to show themselves.
As I type this, the MIG is warming up, I intend to bring my mistress back from the grave!
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K
kerf
Guest
Having decided to bring my bike back from the grave, I began by locating some suitable stock for a spacer to rest against the inner race of the shaft bearing. I finally decided on ½" water pipe and cut one end and filed the beveled edge, from the cutter, to a flat surface. Using my dial indicator caliper, I measured the distance from the banged up shaft shoulder to the bearing race and cut the spacer to that length. I filed the newly cut end to a flat but didn't remove the entire bevel, to allow clearance for the bearing seal. That done I turned my attention to the cracked outer sheave and using the MIG, welded up the cracks on both sides. Where the shaft had wallowed the mounting hole out, I added weld to rebuild these surfaces. A little grinding with the die grinder and reshaping the mounting hole with files, the patched up sheave was done and I was off to the hardware store.
I wanted a washer to go between the spacer and the ramp plate. The one that fit the bill was a 7/16" SAE washer and I checked all they had, with the caliper and picked the thinnest at .053". The bore of the washer was opened about .010" with the Dremel, to fit my shaft. Using trial and error, I slowly filed the spacer down to give the correct mounting for the variator and outer sheave. The spacer came out to .226" and with the washer it gave me a total spacing of .279" off the bearing race. The outer sheave was a press fit onto the shaft and I coned the outer washer to make sure it didn't contact the shaft end. A belt and a little locking compound and she was back together. On the test stand, the variator worked to perfection, smoothly shifting up and down as I operated the throttle.
This rain just won't stop, the sun comes out but before it dries the street, it rains again. As soon as I get some dry road, we'll see if the new life I gave the CVT will hold up. Fingers are crossed.
I wanted a washer to go between the spacer and the ramp plate. The one that fit the bill was a 7/16" SAE washer and I checked all they had, with the caliper and picked the thinnest at .053". The bore of the washer was opened about .010" with the Dremel, to fit my shaft. Using trial and error, I slowly filed the spacer down to give the correct mounting for the variator and outer sheave. The spacer came out to .226" and with the washer it gave me a total spacing of .279" off the bearing race. The outer sheave was a press fit onto the shaft and I coned the outer washer to make sure it didn't contact the shaft end. A belt and a little locking compound and she was back together. On the test stand, the variator worked to perfection, smoothly shifting up and down as I operated the throttle.
This rain just won't stop, the sun comes out but before it dries the street, it rains again. As soon as I get some dry road, we'll see if the new life I gave the CVT will hold up. Fingers are crossed.
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K
kerf
Guest
Changed direction again. I discovered I had a pair new, high quality bearings that would fit the input. I pulled her down again to install the new bearings and while I had the shaft out, I turned the shoulder down to a nice square edge. Selected a couple of washers to give me proper spacing and we're back like new. Just put her through some road work and it's like it never happened. After another 500 miles, if she is holding fine, I'll order a new trans so when this one does go, I'll be ready.
loquin
Well-Known Member
How'd the repair work out, kerf?
K
kerf
Guest
Things look good so far. Took a good long ride Sunday and it worked like a champ. I'm accustom to Staton and I've abused mine but it won't break, these little CVT's aren't as bullet proof as Staton but I think they will work just fine if not beaten like a rented mule. The ride is sweet, pulls off from a standing start, even up hills, it's quieter than Staton and I get no chain surge.
Kerf back to happy!
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