Snake Eater CVT

Full Suspension With CVT

I've been working on this build for several years in my head and at last she's a reality, a full suspension bike, with a hot motor, running through a CVT. I must say, I'm very pleased with the results so far, although I've only had several shakedown runs. That will change tomorrow and big time on Sunday. If everything goes well, I believe I will crossed the line between motorized bicycle and moped. Thanks goes out to Neat Times for his inspiration and consultation on this project.

http://motorbicycling.com/f36/cvt-rack-mount-7265.html

One day a little over four years ago, I found myself staring at a weed whacker engine and a bicycle and pondering, could this work. To make a long story short, I bought a Staton friction drive kit with a Tecumseh TC300 and made my first build. About a week later, I built one for my wife and we began riding together. Always looking for more speed and power, I swapped the TC300 (junk) for a Mitsubishi TLE43 and found what a quality engine was all about. Rough roads were wearing a little thin, so again I upgraded to the Mongoose full suspension and later to a Staton Chain drive. The little lady went through both TC300's so I bought the Chung Yang R460 for me and gave her the TLE43. I created a two speed on the Staton box and it worked well but that CVT bug was always in the back of my mind.

For this build, I wanted speed, power, quite and a smooth vibration free ride. To that end, I used the CVT rubber mounts and added rubber isolators at all other mounting points. The power is routed from the CVT through a 14 tooth sprocket, down to a 72 tooth freewheel sprocket on the wheel. The chain is 8MM, which seemed to be the easiest way to go. I bought a scooter muffler but wasn't happy with the chain saw sound. I gutted the muffler, added about 4" of length to the housing and created a straight through glass pack, with a spiral baffle inside the the core tube. Since I had been running a Staton chain drive, my Staton rear hub had a 16 tooth left hand freewheel. I just pulled down the bottom bracket and swapped the pedal chain to the left side. A quick idler roller and it works like factory, single speed of course.

The bike is quite, accelerates like a car, eats hills and hits 35 mph at 6800 rpm. Don't know about top end yet but the R460 will wind out above 11,000 rpm. I hope I'm back after my hard runs with good news. I've included pictures of the bike, before and after the build.

Well, I've put about 30 miles on the bike and a few issues came forward. When I left Saturday morning at 5 AM, the bike was acting like it was running rich but by the time I got home there was major power loss. The spiral baffle had deformed with heat and restricted the exhaust. Out at 5 AM this morning, sans baffle (need something else, chain saw with wheels) and the performance was back and the ride was really great. The CVT takes some getting used to because when you hit a hill, the bike slows down but engine RPM remains constant as does engine loading. I think I can gear lower because at 35 MPH, she is still below 7K, max torque isn't reached until 8K.

My 14 tooth and 72 tooth, combine for a 5.14:1 ratio. I think I can find an 11 tooth for the trans and I already have a 63 tooth which would be 5.72:1 and the 11/72 would be 6.54:1. Maybe there's something there that would work even better, don't know. What I do know is, 30 miles without ever turning a pedal, in all kinds of big hills, is darn sweet.

Thanks Dave.

Kerf been do'n some cipher'n. The Staton box was geared at 18.75:1 and my chain drive was 1:1, giving me a final drive ratio of 18.75:1 and it let the R460 breathe real good. Before the build I checked the CVT and found the gear box was 3.71:1 and the belt was 1.89:1 in low range, giving me a 7.0:1 total in low range. I could only estimate the belt in high range and I thought 1:1 looked pretty close, giving me a total of 3.71:1 in high range. I just clocked the bike at 35 MPH and it was turning 6550 RPM, so backing into the numbers, the belt looks to be closer to .775:1 in high. That makes a huge difference.

Here are the final ratios available to me:

Trans. high range 2.875:1 - chain 14/72 = 14.79:1 final. (running that now)

If I pick up an 11 tooth trans sprocket, this will be available.

Trans. high range 2.875:1 - chain 11/72 = 18.82:1 final.

Trans. high range 2.875:1 - chain 11/63 = 16.47:1 final.

I'll order the 11 tooth tomorrow.

flying squirrel said:

may i ask were you got the CVT?

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Fancy Scooter.

bowljoman said:

Nice build.

btw: Fancy scooter parts sells a 410 sprocket that fits the CVT and goes very well with BMX chain.

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I pondered the 410 sprocket and may try it one day. The only issue was finding a suitable 410 for the wheel, that would accept the freewheel and have the requisite number of teeth for my ratio. I could probably get Martin Sprocket to build one but that's lots of $$$$$$$.

NEAT TIMES said:

Kerf

Nice Job Of It. I Never Got Around To Making My Brackets Look Cleaner, Like Yours. I Went On To My Diy Shifter Build. I Did Put A Hs Titan 4 Stroke On One Of My Cvt Bikes. I Would Post A Pic With Your Permission.

Did You Read My Thread To Around Post 38 And On? Thats Where I Figured Out How To Have Double Freewheels On The Right Side For $4. Plus Sh. Using The Regular Rear Wheel.

Kerf, Thanks For The Kind Words.
Ron .

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Sure, you're welcome to post anything you wish. I always enjoy looking at your work.

My 11 tooth sprocket is installed on the CVT and I've run it with both the 72 tooth and the 63 tooth. I have also confirmed my calculations on the high speed ratio of the CVT at 2.875:1. The 72 tooth gives me the gearing of my old Staton single speed box but I think I like the 63 tooth. The higher ratio will actually slow the bike on top end because over gearing won't allow the engine to gain full RPM but it will cruse at 35 MPH. I still have more riding to do before I make a final decision but I'm getting closer. My pedals have cob webs on them, maybe I should keep the engine off for a while because my pants are getting tight around the middle.

Don't know that I want to retard the shift point very much but I wish I could adjust the shift limit. The variator will overdrive, I built a small spacer that limited the total amount of variation but where it contacted the inner plate, it would cut into the bushing area. Decided the handle the issue with final gearing instead.

While the 16.47:1 ratio would be too high for a single speed, it only limits my top end. As far as normal riding (25 - 35 mph), it works great. You can't rev the engine into the upper RPM range but you can't lug it either. Under load the CVT just down shifts and the bike may slow but engine loading remains constant. The 18.82:1 makes it a different animal, that will actually run faster but results in a higher cruise RPM.