CVT Completed Frame Mount CVT

Discussion in 'Transmission / Drivetrain' started by Shrapnel, Apr 8, 2009.

  1. Shrapnel

    Shrapnel New Member

    I'm new to this site but wanted to show my own use of the pocket bike cvt on my mountian bike. Here is the setup:

    Zenoah 51cc engine (peak power 3.2HP @ 9000rpm)
    Pocket Bike CVT with 11 tooth pinion sprocket for BF05T 8mm chain
    72 tooth BF05T 8mm chain sprocket mounted on a freewheel

    Back when Staton-Inc still carried the CVT, they said it had 1.9:1 to 1:1.1 variability in the belt/pulley system, multiplied by the 3.714:1 gearbox. I've measured the diameters that the belt rides on the pulley and took apart the gearbox and counted the teeth and got about the same numbers.

    It rides great and will pull me up any hill. Takes off good from a stop and accelerates quickly. I don't know the top speed, but it's about as fast as I want to go.

    Attached Files:

  2. Those 51cc geos are pretty awesome.
    I like the 8mm chain too.
    Good job, I just wish you still had pedals...
    Last edited: Apr 8, 2009
  3. eastwoodo4

    eastwoodo4 Member

    looks like the pedals woulda cleared.
  4. Shrapnel

    Shrapnel New Member

    Yeah, the pedals would have cleared, but the freewheel I'm using only allows for one sprocket to be attached to it. They do make some left-hand threaded freewheels that I could have used with Staton's special hub to make it left hand drive and keep the pedal side free, but I just went with what I had.

    It's more of an "ultralight motorcycle" than a motorized bicycle now. The whole thing weighs less than 50 lbs. If I had any fabrication skills, it'd be a whole lot nicer.
  5. eastwoodo4

    eastwoodo4 Member

    looking at it a little closer i see why u cant pedal it.u know u can attach those cvt`s to the motor in any position u want right?i have one just like it.then u could put it behind the seat
  6. Shrapnel

    Shrapnel New Member

    The first time I built it I mounted the engine on a luggage rack. It really made the bike back heavy. This time I tried to keep the weight as balanced as possible, front to rear and side to side.

    If I do it again, I'll try to mount the engine lower to keep the center of gravity as low as possible. Of course, that means I won't have any shot of putting pedals back on it (but I don't really like pedals anyway, that's why I put the engine on it).
  7. loquin

    loquin Active Member

    Unfortunately, in most states, a motorized bike without pedals is a motorcycle, no questions asked, and needs to be licensed, insured, etc.
  8. Shrapnel

    Shrapnel New Member

    That's one of the perks to living in Indiana. If I had a 50cc engine or smaller (instead of my 51cc), I'd be street legal without any registration. Any scooters in Indiana 50cc and under don't need registration, and you don't need a license to ride them (even nice ones like the Yamaha Zuma).

    As mentioned above, mine doesn't meet the street legality requirements due to engine displacement, but I don't commute on it. It's just a fun project that spends most of it's time in my garage.
  9. heathyoung

    heathyoung Member

    Nice job - you could use a flip-flop hub and run the pedals as LHD, CVT as RHD. Most of those 8mm sprockets have a freewheel that is a standard ISO jobbie, and the lower teeth freewheels (ie. 14/15 for pedal side) are 30X1's - which suits the other side of the hub.
    Last edited: Apr 15, 2009
  10. Shrapnel

    Shrapnel New Member

    I took some pointers from the folks over on and rebuilt the CVT with new bearings and modified the housing as shown in the pics for better cooling.

    I just used some relatively cheap bearings from McMaster-Carr, but it seemed to make a good difference. The bearings I used were all rated for 1500lb axial load, and they were very smooth rolling. I also ditched the grease in the gearbox in favor of 10W30 motor oil. There is a lot less drag in the gearbox now, but the oil leaks slightly where the driven shaft goes through the inside of the CVT box.

    I took the bike out today and clocked it at 35 mph, and it still has enough torque to do burnouts. The only weak point I'm currently having is the freewheel that the rear sprocket mounts to. I've smoked two of them now from abuse. I just need to stop abusing it or find something stronger.

    Attached Files:

  11. heathyoung

    heathyoung Member

    The freewheel is a standard ISO thread, just get a better one that is designed for some serious abuse - SBP sell a serious unit that will fit your hub just fine...

    Its a 5 hole mount, so you would have to redrill your sprocket, but it would be pretty indestructable...

    I wish we could get those CVT's locally in Aus... Dern it...
  12. LOL, I like the swiss cheese belt cover.
    Venting can only help.
    I was one of the main guys at GPN doing a lot of the mods on the CVTs.
    I love these things. For hills, there is no comparison (except a much bigger motor)
    As well, it allows you to run serious gearing and still pull it,
    without overrevving the motor.
    I prefer to max out about 9k rpms, as that's usually where most power is produced with my 2 strokes
    so the motor isn't screaming 12-13k or higher.

    My goal would be to have an upgrade kit for these china CVTs which would have
    1. New variator shaft (with closer tolerances and hardened)
    2. A beefier cap on the driven shaft (those little nubs can keyhole the thin sheet metal cap quickly, messing up the shifting.
    3. A freewheel mounted at the sprocket output.

    Did you play with the belt tension (re. shim?)
    It can make or break the tuning of that CVT.

    My big problem with the vari shaft was that it did not fit well in the
    clutch bearing's inner race. It spun freely inside them.
    Thus it would wobble slightly, and shifting smoothly suffered.
    I JBwelded it into the races once, and they it ran so good until the JB weld busted out.
    Maybe Threebond 1211 will do the trick, or a hammer and some
    thin copper shim material. If there was only a third bearing at the end of the variator shaft, so many problems would be avoided.
  13. Shrapnel

    Shrapnel New Member

    I tried tuning the CVT before I rebuilt it and just made it work worse. I first tried removing 3 of the variator weights, then shimmed the rear spring, but was never as satisfied with the results as when I just ran it stock. So for right now, I run it stock.

    I've ordered some variator weights so that I'll be able to make small incremental changes to it. I don't really plan on shimming the rear spring at all. That just made it stay in torque mode all of the time and killed my top end.

    My engine is stock as well (Zenoah 51cc).
  14. Fair enough.
    Being that the motor is stock with no tuned pipe,
    sounds like you're ok.

    When you get the weights, I'm sure finding a mid way point
    between 30g and 15g will have you performing better.
  15. Nuttsy

    Nuttsy Member

    Yeah, I tried removing 3 weights with similar (poor) results. Will be waiting to hear if slightly different weights will kick it up a little.
    About the only thing so far that made a HUGE difference was changing bearings and I went overboard and filled the gearbox with 80W90 gear oil that I had on hand. I did the both at the same time so I don't know which one is the clear winner but that CVT does NOT whine anymore!:whistling: Now its just motor sound again like when the Robin was a friction drive. I may try poking a FEW holes in the case. Shrapnel, have you noticed any belt 'dust' coming out since venting the cover? I won't like it if it gets messy :rolleyes7:
  16. Shrapnel

    Shrapnel New Member

    I haven't had any problems with belt dust yet. I left the top and bottom of the cover solid, and only drilled holes on the side and back. Most of the belt dust still collects inside the cover. My cvt used to get really hot, but after the swiss chesse effect the cooling seems to be stable.

    I don't know if I really created any more cooling flow, but I have enough holes that no heat is ever going to be trapped inside. I'd run it open if I could, but that would create a safety hazard with were the engine is mounted.