79cc Predator and CVTs

knightscape

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Jul 29, 2013
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Has anyone built a 79cc Predator with either a Comet or the GTC clone CVT using stock parts rather than shimming the engine output shaft out from 5/8" to 3/4"? I've found old threads on shimming, but none on replacement pulleys. I see that Comet and GTC both have aftermarket driven pulleys that can be swapped in to the CVTs to fit a 5/8" bore CVT output. I haven't yet found a replacement drive pulley for 5/8" engine output shaft. Does it just not exist or is my google-fu lacking?
 

racie35

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Nov 17, 2012
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No one makes that driven unit...and the way the 3/4 are made presents a problem for shimming..the key is part of the driven unit,otherwise it would be easy.
That said, when it is done,most people here feel a cvt(tav) eats up too much power on smaller engines. I don't buy into it really cuz 50cc scooters have em...I think you'll hafta try one
 

FFV8

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Oct 29, 2013
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You have to use a 1" bore driver, and make a bushing with keyways 180 degrees apart.

It worked well for a while. The Comet system puts a substantial side load on the engine shaft as it upshifts. After I snapped the second 5/8" crankshaft off flush with the case, I decided I knew why Comet does not make a 5/8" unit.

The Lifan 4mhp 118cc engine has a 3/4" shaft. My Comet drive on that engine has been a solid performer, while hauling the sidecar around too.

Just use a Hilliard clutch on the 79, and use the 3,000 rpm springs. It becomes the torque converter...
 

mdlee1958

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Feb 22, 2009
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Fort Collins, Colorado
Having built 3 of these sleeves/shims myself, I will offer up what I have encountered. The 3 engines I have done this for are, HauSheng 49cc, Predator 79cc and Predator 99cc. The first 2 were HS 49cc and Predator 79cc, and used the Comet/Clone CVT with a 3/4" driver. I machined my own bushing/sleeve and found that the way that the new comet clones are made with integral keyway the bushing becomes very thin and makes keying to the crank a PIA. On the third one I wised up and bought a 1" driver. Why you ask? Because machining a 5/8" to 1" bushing s much easier and allows it to be thicker and stronger. Another side benefit is that the 2 that are 5/8 to 3/4 seem to have balance issues (not too horrendous) but still an issue. The 5/8 to 1" bushing seems to run smoother. Just my 2 cents.
 

GoreWound

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Dec 1, 2014
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The 3 engines I have done this for are, HauSheng 49cc, Predator 79cc and Predator 99cc. The first 2 were HS 49cc and Predator 79cc, and used the Comet/Clone CVT with a 3/4" driver.
sorry about this question being a little off topic.
How well did the Huasheng run with that on there?
I want to do this and have been having no luck finding anyone out there with hands on experience.
I have a heavy bike with a 20in rear wheel that I want to use to tow a trailer, my theory is to use a torque converter going from a ten tooth output to possibly an 80 tooth or higher on the rear wheel.
really anything you want to mention about your experience combining the HS-142f with a torque converter I want to hear it.
 

knightscape

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Jul 29, 2013
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Maine
sorry about this question being a little off topic.
...
really anything you want to mention about your experience combining the HS-142f with a torque converter I want to hear it.
Not off topic for me, my main bike is a 142F. Thanks for the replies guys. The only CVTs I've seen for 49cc are pocket bike systems that are all a little on the small looking side and none directly compatible with the huasheng. I've been thinking about a 79cc or 99cc predator build with a CVT (I've never worked with a CVT), Maine law doesn't specifically limit by CC size, but I'd be afraid that a 212cc which a CVT would bolt right up to might draw a little more attention than I'd want to push with the law. I guess I'll keep reading the old threads about working with bushings. I'm surprised no one makes an off the shelf product for the 79/99cc motors I'd think they'd be perfect for small karting projects and particularly Comet and GTC already have the rest of the parts ready to go, they just need the drive clutch. I dunno I guess, I'm not a kart guy.
 

mdlee1958

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Feb 22, 2009
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Fort Collins, Colorado
The HS142 never really seemed to be able to utilize the upper end of the CVT range. I was using it on a jack shaft shifter and in the upper gears would not have enough overlap to keep the engine from bogging down in 4th and 5th gears.
 

dtv5403

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May 4, 2015
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How did the 79cc perform with the cvt? Would you consider making and selling the adapter bushings?
 

GoreWound

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The HS142 never really seemed to be able to utilize the upper end of the CVT range. I was using it on a jack shaft shifter and in the upper gears would not have enough overlap to keep the engine from bogging down in 4th and 5th gears.
I'm hoping to mostly be using the lower end of the CVT, my thoery being that with a small rear wheel, and lots of weight on the bike I can just put the engine at max torque and let the CVT worry about the rest untill I get to speed. I am also figuring I would need an unreasonably large driven gear on the rear wheel.

my life would be much easier if manually operated gears weren't a no-no here.
 

mdlee1958

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Feb 22, 2009
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Fort Collins, Colorado
DTV, the 78/99cc engine runs very well with the CVT. In fact it is at the moment my main rider. With a jackshafted shifter setup it cruises quite nicely between 35 and 45 mph pulling a trailer with anywhere between 50 and 100 lbs of cargo. Gore, if speed is not an issue, I would put a 52 to 60 tooth rear sprocket. You probably would only top out at about 30 but you'd have a lot of torque from the start and for pulling a trailer.
 

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knightscape

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Jul 29, 2013
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mdlee1958, do you have a build thread or album of that bike? I'd love to see as many pics as you feel like posting of that thing.
 

dtv5403

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May 4, 2015
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I'm curious, why did you hook a shifter up to a cvt? It seems kind of redundant to have two shifting systems.
 

dtv5403

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May 4, 2015
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I'm thinking of doing a hub jackshaft anyway, as ffv8 mentioned above, seems kinda risky putting such a huge side load on a 5/8 shaft. I have the agk jackshaft, gonna see about putting a hub jackshaft between the agk jackshaft and the rear wheel, hub jackshaft would be 1:1, on external gearing would be the same, 13.58:1, and would really on internal gearing of the hub jackshaft for shifting. Seems the simplest way to shift without putting an extensive side load on the crank shaft.
 

dtv5403

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May 4, 2015
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The predator shafts tend to have a few mm of play, that could be why he snapped a couple crankshafts. But all that aside, I'm pretty obsessed with manual shifting for some reason and manually controlling a cvt is a fairly complicated endeavour that I don't possess the knowledge or skills to complete. A fixie hub used as a jackshaft is actually way less complicated. Not cheaper considering I want a draggin skin clutch to go with it, but still less complicated. Going to run it as a single speed until I can afford the clutch and fixie hub.
 

curtisfox

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Dec 29, 2008
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I often wondered how a CVT off a moped would work,like off a Honda.

We have the same law here GoreWound,in MN. anyway. 50cc max. and 2hp, auto shift only................Curt
 

MEASURE TWICE

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Jul 13, 2010
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I have a 3.5 hp Briggs and it has a 3/4 crankshaft with a 3/8 thread tapped inside the end of the crank shaft. There is a keyway for 3/16 key, but the length of the shaft is a stubby 1.33 inches. I don't see how other than using a pulley it can be used.

Do all the centrifugal clutches and torque converters need more length to have them assembled onto the shaft than 1.33 inches. I know shaft extenders and are available, but are a bit pricy and they have an unusable area where they clamp over the existing shaft which then makes existing work I've done need to be further spaced from the crankcase wall.

Buying another crankshaft that would fit the engine could be much better idea, but no way would I buy a new part at the cost involved, I could instead sell the engine and just get another used one that is right for the job.

Meanwhile I use another slightly older engine 3hp (less 1/2 hp) also a Briggs and it is 5/8 shaft using belt drive Max Torque clutch with it on my bike. The jackshaft I have and the sheave get the ratio I like, but automatic converter and a bigger engine I have would like to see if can use it instead.

Looks like from this page on 30 series there is a driver that is 3/4" and the driven is 5/8". Since I use 5/8 jackshaft and that is where the driven could go I wanted to try that. See if I think that drawing shows where the 3/4" shaft is to be at least 2 an 7/8 inch from the diagram?

https://www.gokartsupply.com/asymapp.htm

MT
 

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MEASURE TWICE

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Jul 13, 2010
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Step up shaft adapter 3/4 to 1 inch and 1 inch has keyway for 1/4 key. Amazon has one from Climax Metal Products for about $30 but it does not have a keyway.

Checking price on the Stafford part that has the key slot.

http://www.staffordmfg.com/ProductDetails.aspx?partNumber=5EL012K&fromUrl=Home.aspx

I found this and it could work also may cost more than the engine with edger I bought. Will soon see if I sell the engine to buy another used or keep it for something else. I can use the engine on the bike but it being short shaft will only be as is useful to attach a pulley, no torque converter.

The centrifugal clutch I have is 5/8 shaft for the slightly smaller 3hp Briggs, but if I bought a belt clutch it would also require more shaft length. Buying a crankshaft for the engine to swap out could be only if eBay had one for low cost. I saw old mini bikes forum thread that a few years back a guy bought on eBay a Briggs crankshaft for longer shaft to swap in for $15. Trying to get the right dimensions, and I guess what is call the journal, what two areas support each side of the shaft, to be the right diameter is important. The throw that the crank goes (piston travel).... etc. This for 3.5 hp Briggs model 91212 0219 01.

I'm not sure how riding in the woods with no clutch and when you stop the engine stops from direct pulley belt drive would be. Probably not as easy as with the belt clutch I have now with the smaller 3hp Briggs.
 
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