Gc160 chopper bike and 79cc friction drive

Phillybound313

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Feb 4, 2019
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Hi, new here. Im a welder by trade and succesfully built a friction drive mountain bike using a 79cc predator motor that hinges on the front fork. Almost stock (governer removed, pz19 carb stock and header) with 2 7/8 od black pipe it clocked through speed trap going 36mph on flat. Climbs hills pretty good as well. Ive recently port and polished head(smoothed casting imperfections, smoothed transition top of each bowl near valve guides, and knife edged valve guides in bowl, port gasked matched exhaust and intake, took off .050 using glass and sandpaper (around 10:1 compression), added another spring inside valve springs (about 16-20lb total each spring), welded and drilled new pushrod dimple stock rocker arms to create about a 1:3 ratio (around .220-.230 lift), and filed .036 off flywheel key(around 8 degree timing advance). Im currently drilling stock jet starting with a .80mm #80 jet size in pz19 carb. Im working on that today, thinking around #90-100 or so. Hoping for around 5-6 hp @ 6500-7000 rpm. Also hoping for at least a top mph increase of 5 mph with the added rpm and power without having to increase 2 7/8 od drive spindle.

My newest build is a gc160 motor(5hp stock) and jesse james chopper bike. Ive removed governer, going to use a pz22mm carb, header, and going to increase rocker arm ratio for more lift and added spring in stock springs. Hoping for 6-7hp.
Id like to use a 20 inch rim to make a pulley that will be welded to rear 20 inch rim, and make a clutch using a spring loaded idler pulley in the rear that adds tension to v belt for drive engagement.

My idea and question is regarding the operation and mechanics of a cvt driver pulley.
My idea is to only use a cvt driver pulley that is in the size range of 2-3" for a gear ratio of 10:1 - 6.66:1 with the 20 inch back rim pulley. Since the back idler pulley will be spring loaded, it should keep tension on the belt at all diameters of gear ratio.
Am I understanding the mechanics of the driver of a cvt properly? Doesnt the driver push out and change gear ratio with torque or load output of engine? Doesnt the driven portion of the cvt stall like a centrifugal clutch and stall, or engage at a certain rpm? Is this accurate? If im using an idler pulley to put tension on belt for engagement, do you think this would work?
So far ive found a 1 3/4 inch od driver making the ratio around 11.43:1 ratio which would be just fine. Also, can anyone tell me the approximate od range of a cvt driver? Im hoping it wont exceed too far past 3" or a 6.66:1 ratio. Should be good to 40-50mph. Any ideas?
 


Will'smotobikes19

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Apr 9, 2018
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79cc friction never seen that done before. My 2 stroke will go 37mph. I’d like to mod my 79cc chain drive. Had a top speed of like 30mph even. One thing I think you can do is take stock 212cc springs and use them in the 79cc to prevent valve float. I will try it as I’m upgrading my 212 springs anyways. Don’t know much about gear ratios but some others might.
 

Phillybound313

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Feb 4, 2019
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Thanks man yes these little 79cc's are decent motors proven to be pretty stought.
What size sprockets do you run for the 30mph?

You are correct about the 212cc springs being used. The most common i believe are the 18lbers, and im hearing of a shop thats run 26lb with a custom cam and 12:1 compression @ 7500-8k rpm using stock rod and flywheel reliably.
 

Will'smotobikes19

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Well there’s a jackshaft and I’m not sure how many teeth there are I’ll have to count. I was running a 40 tooth sprocket on the wheel. It’s just the stock gasbike transmission. The 79cc is the same price as a China 2 stroke about $100 but I’m betting they last much longer because of the oil bath there is better lubrication in the 4 stroke. I need to get my kickstand mount welded back on (crappy factory welds).
 
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Phillybound313

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Feb 4, 2019
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Well there’s a jackshaft and I’m not sure how many teeth there are I’ll have to count. It’s just the stock gasbike transmission. The 79cc is the same price as a China 2 stroke about $100 but I’m betting they last much longer because of the oil bath there is better lubrication in the 4 stroke. I need to get my kickstand mount welded back on (crappy factory welds).
Im willing to bet youll get years out of that at least out of the engine. Before i built this with a new motor, i had the older 2.5 greyhound motor on it with governer removed, and header. I bought a pz19 carb (the 20 dollar knockoff) and threw it on this bike the a centrifugal clutch bell, and the 2 7/8 drive spindle. It sarted right up and i ran it as daily transportation here in philadelphia for about 4 months. Finally, the flywheel bolt came loose (forgot to torque down), and cracked the crank output shaft. I tried to v groove the crack and weld, but only had access to a 85 amp flux core wire feeder, and couldnt penetrate enough weld to stack in there, so decided to get a brand new predator. There is about another 4 months of daily ridden use on tjis motor with governer removed, pz19 carb and header.
Ive just recently did all these modifications, and about to test run it with the better weather.
I would think with removed governer, bigger or drilled jet, air filter and header youd see 35mph minimum even with stock springs with nothing else changed. Just removing governer really wakes these motors up.
 

Phillybound313

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Feb 4, 2019
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iup.im
Im willing to bet youll get years out of that at least out of the engine. Before i built this with a new motor, i had the older 2.5 greyhound motor on it with governer removed, and header. I bought a pz19 carb (the 20 dollar knockoff) and threw it on this bike the a centrifugal clutch bell, and the 2 7/8 drive spindle. It sarted right up and i ran it as daily transportation here in philadelphia for about 4 months. Finally, the flywheel bolt came loose (forgot to torque down), and cracked the crank output shaft. I tried to v groove the crack and weld, but only had access to a 85 amp flux core wire feeder, and couldnt penetrate enough weld to stack in there, so decided to get a brand new predator. There is about another 4 months of daily ridden use on tjis motor with governer removed, pz19 carb and header.
Ive just recently did all these modifications, and about to test run it with the better weather.
I would think with removed governer, bigger or drilled jet, air filter and header youd see 35mph minimum even with stock springs with nothing else changed. Just removing governer really wakes these motors up.
Im willing to bet youll get years out of that at least out of the engine. Before i built this with a new motor, i had the older 2.5 greyhound motor on it with governer removed, and header. I bought a pz19 carb (the 20 dollar knockoff) and threw it on this bike the a centrifugal clutch bell, and the 2 7/8 drive spindle. It sarted right up and i ran it as daily transportation here in philadelphia for about 4 months. Finally, the flywheel bolt came loose (forgot to torque down), and cracked the crank output shaft. I tried to v groove the crack and weld, but only had access to a 85 amp flux core wire feeder, and couldnt penetrate enough weld to stack in there, so decided to get a brand new predator. There is about another 4 months of daily ridden use on tjis motor with governer removed, pz19 carb and header.
Ive just recently did all these modifications, and about to test run it with the better weather.
I would think with removed governer, bigger or drilled jet, air filter and header youd see 35mph minimum even with stock springs with nothing else changed. Just removing governer really wakes these motors up.
Im actually using a kickstand welded on the handlebars as a clutch lever to pivot the motor and spindle onto the front tire
 

Will'smotobikes19

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Messages
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I have a little ryobi 31cc I want to do that with. Front wheel drive friction. I have a bike peg that might work. Your Honda build is going to be cool I have a mini chopper frame I’m going to put a 212 hemi on.
FAB14ED9-FEE5-4BFE-BB84-7B0712470D89.jpeg
 

curtisfox

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May 13, 2010
Messages
620
Hi, new here. Im a welder by trade and succesfully built a friction drive mountain bike using a 79cc predator motor that hinges on the front fork. Almost stock (governer removed, pz19 carb stock and header) with 2 7/8 od black pipe it clocked through speed trap going 36mph on flat. Climbs hills pretty good as well. Ive recently port and polished head(smoothed casting imperfections, smoothed transition top of each bowl near valve guides, and knife edged valve guides in bowl, port gasked matched exhaust and intake, took off .050 using glass and sandpaper (around 10:1 compression), added another spring inside valve springs (about 16-20lb total each spring), welded and drilled new pushrod dimple stock rocker arms to create about a 1:3 ratio (around .220-.230 lift), and filed .036 off flywheel key(around 8 degree timing advance). Im currently drilling stock jet starting with a .80mm #80 jet size in pz19 carb. Im working on that today, thinking around #90-100 or so. Hoping for around 5-6 hp @ 6500-7000 rpm. Also hoping for at least a top mph increase of 5 mph with the added rpm and power without having to increase 2 7/8 od drive spindle.

My newest build is a gc160 motor(5hp stock) and jesse james chopper bike. Ive removed governer, going to use a pz22mm carb, header, and going to increase rocker arm ratio for more lift and added spring in stock springs. Hoping for 6-7hp.
Id like to use a 20 inch rim to make a pulley that will be welded to rear 20 inch rim, and make a clutch using a spring loaded idler pulley in the rear that adds tension to v belt for drive engagement.

My idea and question is regarding the operation and mechanics of a cvt driver pulley.
My idea is to only use a cvt driver pulley that is in the size range of 2-3" for a gear ratio of 10:1 - 6.66:1 with the 20 inch back rim pulley. Since the back idler pulley will be spring loaded, it should keep tension on the belt at all diameters of gear ratio.
Am I understanding the mechanics of the driver of a cvt properly? Doesnt the driver push out and change gear ratio with torque or load output of engine? Doesnt the driven portion of the cvt stall like a centrifugal clutch and stall, or engage at a certain rpm? Is this accurate? If im using an idler pulley to put tension on belt for engagement, do you think this would work?
So far ive found a 1 3/4 inch od driver making the ratio around 11.43:1 ratio which would be just fine. Also, can anyone tell me the approximate od range of a cvt driver? Im hoping it wont exceed too far past 3" or a 6.66:1 ratio. Should be good to 40-50mph. Any ideas?
LOL
1549301857594.png

Your 10:1 ratio sounds about right. The rear of CVT is like the spring loaded one in this picture, expands and opens up under pressure along with the front as it contracts. You have to watch the CVT you get i here some have a belt with flat side on one side, and a taper on other side........Curt
 

Will'smotobikes19

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Apr 9, 2018
Messages
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It’s cool that you daily drive your builds. I’d like to do the same once I get a more reliable one put together. I have a little 49cc electric start motor I have plans for just want a bike that probably won’t work (without mounting bracket mods). I like it because it has 3 inch tires and dual discs. I’m on the other side of pa. My current job is about 10 miles away so 20 miles a day. 16 mpg is pretty bad compared to what a bike with a motor can do, my daily is an suv. Hopefully you can get the right ratios for the Honda bike.
 

Phillybound313

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Feb 4, 2019
Messages
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LOL
View attachment 85851
Your 10:1 ratio sounds about right. The rear of CVT is like the spring loaded one in this picture, expands and opens up under pressure along with the front as it contracts. You have to watch the CVT you get i here some have a belt with flat side on one side, and a taper on other side........Curt
I have a little ryobi 31cc I want to do that with. Front wheel drive friction. I have a bike peg that might work. Your Honda build is going to be cool I have a mini chopper frame I’m going to put a 212 hemi on. View attachment 85850
Looks good bro!! I like the gauge cluster you have on there a lot!
Not sure how a 31cc would do. I have a 33cc poulen pro i was thinking of runming but still sitting. Something i have seen that might interest you especially with a smaller motor like that is a guy who took a rear derailer, and mounted it on the front with a gear reduction box he made. Ill see if i can find it. You already look like your forks have enough clearance to run a back tire on the front with a derailer.
I have a little ryobi 31cc I want to do that with. Front wheel drive friction. I have a bike peg that might work. Your Honda build is going to be cool I have a mini chopper frame I’m going to put a 212 hemi on. View attachment 85850
I like the frame. The great thing about the friction drive is there really is no gear ratio, and tire size isnt a factor. Its all dependant on spindle size. That looks to me like a smaller tire.
I have a 33cc poulan pro motor that i thought about another build. Im not sure how it would do up hills, but if you get the spindle size right , it may do just fine. Along with 10,000 rpm, it should do decent up top as well.
Another thing that might interest you, i found a build a while back of a guy who used a small motor, homemade gear reduction box ,derailer, and a back wheel with cassette as a transmission, front wheel drive. Similar to a shift kit, without the freewheel sprocket on bottom bracket. It certainly looks like you have enough room between those forks.
The friction drive has been a work horse commuter though, and hasnt really caused any issues aside from wet weather, where i put tension on motor with my leg for more friction on tire. If i goose the throttle im able to cruise along around 15-20 mph in the pouring rain.
Been meaning to make another spindle with a smaller diameter, and jb weld some sand to it just for the raon, but havent gotten around to it
 
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