Snake Eater CVT

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happyvalley

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Jul 24, 2008
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Thanks for the update, been following the thread with interest. I've got one of the chrome cover jobs on a shelf unused that I picked up last winter. I'd be real interested to know the detailed particulars on any upgrades you modded and think should be on a new piece.
 

kerf

New Member
Jun 28, 2010
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Birmingham, Al
I’m more than happy to share everything I’ve learned in my experience with this CVT. As previously explained, I damaged my first tranny by forcing it up a steep hill with improper gearing. That damaged the variator but in doing so it also uncovered what, IMO, are weak points in the design. All the sequent modifications I made to repair the old box were incorporated into the new one.

The first thing is to achieve proper gearing, as I am running the Staton rear wheel, which allows the installation of a left hand freewheel, I moved my pedal drive to the left side. This results in a single speed pedal system but as I’ve stated, I don’t pedal much anymore. The sprockets for the CVT are 8mm so I chose to stay with that chain. I found the best gearing for me was an 11 tooth on the tranny and a 72 tooth on the right side freewheel. My calculations indicate a 45.90/1 ratio in low range and 18.82/1 in high range. In actual operation, I believe the variator will overdrive more than I figured, so the actual high range may be slightly higher.

The CVT is designed to run in the horizontal position and I am mounting in the vertical position. This messes up the secondary gear box venting, which is a problem because this box must be wet lubed. Others fixed this by replacing the vent plug with a solid bolt but I felt that might facilitate oil leakage due to pressurization from heating. I devised a venting system that corrected this issue by installing a reservoir tube through the vent plug hole that keeps the oil in and the pressure out. More on that later.

The first step is a total disassembly of the tranny. The only parts not removed were the gear box bearings, as this requires heating the case to remove them and I’ve had no issues with the OEM parts. The entire tranny has been sprayed with a silver paint and that includes the inside of the gear box, this should be removed with a liberal washing with brake parts cleaner until it’s gone. Once that is done, place masking tape over the inside vent baffle of the gear box and carefully drill out the plug threads with a 21/64” drill bit, being careful not to drill too deep and through the baffle. Once drilled, the hole is tapped with a 1/8” pipe tap, so that it will accept the vent system. Remove the tape and clean the entire case until it’s squeaky clean, with no sign of metal cuttings.

I discarded the stop washer that acts as a stop for the inner variator plate and using a 5/8” bronze flange bushing, cut to .210” long, made a spacer that acts as a stop and transfers the load to the inner bearing race in the shaft bearing. The shaft bearings were replaced with two SKF 6002-2RSJEM bearings and I replaced the oil seals, this time with seals from Rocket Seals Rocket Seals in their nitrile line as they are much cheaper. The last change and the most tedious was reinforcing the outer variator sheave plate by shaping a 5/16” washer to fit the variator shaft and welding it on the sheave. The completed parts looked just like the previously posted pictures of the old parts.

The new vent system is just like the old one except it now is made entirely from 1/8” pipe fittings which seals up much better. The gear box was filled with Mobil 1 75w-90 synthetic gear oil and this has to be done before the tranny is installed. With the tranny in the horizontal position, the oil is forced up through the vent until it comes out through the drain hole which will be on the upper side. Once that is done install the drain plug and the vent system and add oil to the reservoir until there is about ½” up the reservoir tube. Any air left in the box will work its way out through the vent while running, just add oil when necessary.

That's just about all there is to it.
 

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happyvalley

New Member
Jul 24, 2008
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Thanks for the recap Kerf.

Yeah the thin inside washer looks pretty chinzy. So, the bronze bushing you made to replace it goes just to the shoulder on the shaft where the washer butted, right?

Also, I'm curious if you notched the washer you welded to fit the flats on the shaft?

Thanks again.
 

kerf

New Member
Jun 28, 2010
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Birmingham, Al
The original stop washer butted to the rather small shoulder formed by the portion of the shaft the bearings ride on. The bronze bushing slips over the bearing step on the shaft and contacts directly against the inner bearing race and extends out to the end of the bearing step on the shaft.

As to the reinforcing washer on the variator sheave, I cut a thin strip of electrical tape and wrapped it around the threads on the end of the variator shaft. This built the threaded area up so it would hold the 5/16" washer center on the shaft. With the washer centered and held against the end of the shaft by the shaft nut, I sprayed the washer with black paint so that when the washer was removed, the outline of end of the shaft was visible. I used a Dremel and small files to cut the washer hole to a tight fit on the shaft. I placed the sheave on the shaft followed by the washer and a hardware store nut, this held everything together for MIG welding. After grinding the welds down with a die grinder and sanding disk, the welds disappeared and the washer just melded into the sheave.
 

kerf

New Member
Jun 28, 2010
304
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Birmingham, Al
Hello cvt friends

reading the forum post`s a bit more lately. Have been in the house boat mode for some time. Have not run my two cvt builds since 2009. The alcohol in gas drives me nuts, my bikes sit in the sun too much, causing carb problems.

Built the shifter bike and love that. Then converted an axle mount electric to 49cc gas engine axle mount, also like it. Around the first of the year i got a super deal on a 2008 ne5 whizzer, head bolts were loose, got new head gasket, but have not installed it.

Kerf glad your still trucking along with the cvt.

Last week, ran across the "cobrafreak" 200cc hf eng with the comet cvt build thread. That motor was on sale this past week end for $65. Out the door, tax included. The comet drives are less than $200. Delivered. Might do a build like that this winter (in the florida panhandle ! Ha ha . Lived in n wisconsin for over 40 yrs). This is my kind of winter, here!

What do you guy`s think ? Thinking it will be an awsum bike if the large cc is not a problem. Would prefer rear belt drive, clean and quiet.

Ron
The Comet has no secondary reduction so you're gonna need a a jack shaft of some sort. If you were to use something like a Whizzer wheel sheave, with a small pulley on the CVT output, that might get you in the ballpark.
 

NEAT TIMES

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May 28, 2008
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Kerf

Hi Ole friend. I just deleted that post, then just found your reply ! Had a feeling it was off thread. Thanks for the reply.

Maybe the big eng won`t need the reduction. Nearing 61 yrs ago my diy mab, no pedals involved, was a direct drive. Had an old 3/4 hp bs and whizzer rear sheave and small regular pulley on the motor, no clutch. Just push and jump on. Worthless in hills, but rode it all over the county.

Cvt is an awsum option. I want something i can cruise with dependably.

Need to get shutoff valves on all my builds and run carbs dry after each ride, or drain carbs.

Have the 11 tooth / 72 tooth 8mm on my titan 49cc 4 stroke cvt. More starting out power than needed, top speed less than 30 mph. But i go near 300 lbs. Have not rode for months, miss that.

Ron .cvlt1
 

kerf

New Member
Jun 28, 2010
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Birmingham, Al
I'm a little long in the tooth and a little heavy too. Doctor's on my butt to trim down gonna have to I guess, knees starting to hurt when I pedal. I got the wife back on hers a couple of weeks ago, first time since she broke her shoulder riding into a ditch last July. She was a little skittish at first but she's gonna be fine.

Got a 20" bike for my 7 YO grand daughter and taught her to ride last Wednesday. She did pretty good considering she has never tried before. A few scrapes and bangs, had to remind her several times that "Pa don't do drama". She was showing me a little bruise on her leg, I said there wasn't anything there and walked off. She followed me and said, "Pa, you need your eyes checked". Seven going on forty I guess.

I'll be 61 in August, all in all things could be worse, I'm still on the up side of the dirt.
 

happyvalley

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Jul 24, 2008
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upper Pioneer Valley
Good stuff, thanks for taking the time to write it out, now I think I got my thick head around it. (I'll be 61 in Aug too, lol) I'd read through a bunch of the threads at GPN but hadn't seen anything specifically that addressed that inside variator washer or the beefing up of the outside sheave.
 

kerf

New Member
Jun 28, 2010
304
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Birmingham, Al
Good stuff, thanks for taking the time to write it out, now I think I got my thick head around it. (I'll be 61 in Aug too, lol) I'd read through a bunch of the threads at GPN but hadn't seen anything specifically that addressed that inside variator washer or the beefing up of the outside sheave.
The GPN guys never went as far as I did, however robotguy and I did have PM conversations about the tendency of the outer variator sheave to wallow out around the shaft hole. I know that mine failed after the washer failed, as this allowed the sheave to become loose on the shaft. Keep in mind that neither pocket bikes nor the GPN guys are trying to turn a 26" wheel, that large a wheel can quickly overload the tranny if the gearing is too high.
 

happyvalley

New Member
Jul 24, 2008
784
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upper Pioneer Valley
The GPN guys never went as far as I did, however robotguy and I did have PM conversations about the tendency of the outer variator sheave to wallow out around the shaft hole. I know that mine failed after the washer failed, as this allowed the sheave to become loose on the shaft. Keep in mind that neither pocket bikes nor the GPN guys are trying to turn a 26" wheel, that large a wheel can quickly overload the tranny if the gearing is too high.
Yup to the 26" wheel and why I appreciate the trial and error you went through to get it better. I'm in the planning stage of using the CVT with a Robin in the middle of a stretched frame, just behind the seat post, and using a diy jackshaft with dual freewheels to the rear cassette cluster of the bike. I have the drive train planned out and now working on getting a frame made or an existing frame modded.
 

kerf

New Member
Jun 28, 2010
304
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Birmingham, Al
Yup to the 26" wheel and why I appreciate the trial and error you went through to get it better. I'm in the planning stage of using the CVT with a Robin in the middle of a stretched frame, just behind the seat post, and using a diy jackshaft with dual freewheels to the rear cassette cluster of the bike. I have the drive train planned out and now working on getting a frame made or an existing frame modded.
That's a very interesting idea. It gives you the ability to maintain the horizontal mounting, solving the vent issue and achieve the desired gearing. Freewheeling these things is paramount because they don't like to turn w/o the engine due to belt drag. As for me, going to a hard-tail isn't an option as "my butt done got spoiled real good".
 

kerf

New Member
Jun 28, 2010
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Birmingham, Al
LoL, I hear you. I'm planning on using suspension forks and picked up one of these off craigslist: http://www.spadout.com/images/nwiki/286_o.jpg but nothing like a sprung swing arm.
I've used shock absorbing seat post and they do help. I have also put some thought into the "ultimate" frame, something like a light motorcycle frame with a bottom bracket. Could be easily done, unfortunately we will have to DIY because the bike industry is all about grams of weight not heavy duty. Still a big cruiser front triangle with a swing arm and a couple of spring loaded shocks is always in the back of my mind.

Wife gonna toss me out one day I guess.
 

kerf

New Member
Jun 28, 2010
304
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Birmingham, Al
Yes I did, three 3/4" holes up each side of the plastic cover. Unfortunately I discovered that while rolling along at 30 mph and thinking about all that nice cool air flowing through my tranny, it was actually drafting and pulling exhaust oil into the belt. I covered the rear facing holes with foil tape and am just operating with the three on the front side.