4 stroke with sickbikeparts jackshaft
- Thread starter toker_ace
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The Lifan flathead engine was replaced with the OHV engine, though some old Lifan info on the internet still lists the information. Motomags advice on finding a used one is a good place to start your search.
Rick C.
How reliable is a bike derailleur under this kind of power? Should a single speed straight chain line be a design goal?
Maybe a single speed, TAV2, or Internaly geared hub?
Maybe a single speed, TAV2, or Internaly geared hub?
I don't build pull start motors, bad shoulder, but many examples to study on this forum. Study and learn. CVT drive trains seem to be popular with these motors and can run a real chain rather than go jack shaft to a bicycle shifter and the tiny chain. Break the only chain and you have to push it home. I like a pedal chain & a motor drive chain as well, break one and still can use the other to get home. Geared hub same problem, one chain runs everything, and it's a tiny chain at that.
Single speed with a good "Bully" clutch, coupled to a correction gear/reduction gear to run a twin chain for the engine is a good option as well. Check out Sportsman flyers web sight for examples of single speeds etc.
Rick C.
Single speed with a good "Bully" clutch, coupled to a correction gear/reduction gear to run a twin chain for the engine is a good option as well. Check out Sportsman flyers web sight for examples of single speeds etc.
Rick C.
If I may
This is my R&D build, and my first four stroke. Don't do mag wheels, they're too heavy. Go 8 speed for the gear range, and do the x.8 (sorry, it's the X.4) system from SRAM with a 40t-11t range cassette. You'll get crazy acceleration off the line. I also had to swap my mechanical AVID BB7s with mechanical hydro BB7s to compensate for the heavier wheels.
Be aware that your drive side chains may bind once you start shifting up. Take actions to ensure this does not happen, such as increasing the gap between sprockets or adding in a slip disc (a metal disc made to prevent chain binding)
This is my R&D build, and my first four stroke. Don't do mag wheels, they're too heavy. Go 8 speed for the gear range, and do the x.8 (sorry, it's the X.4) system from SRAM with a 40t-11t range cassette. You'll get crazy acceleration off the line. I also had to swap my mechanical AVID BB7s with mechanical hydro BB7s to compensate for the heavier wheels.
Be aware that your drive side chains may bind once you start shifting up. Take actions to ensure this does not happen, such as increasing the gap between sprockets or adding in a slip disc (a metal disc made to prevent chain binding)
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Oh, a few more things I forgot to add:
If you are running without the transmission the kit comes with, use a 28t sprocket after the clutch as the bare minimum. Anything less will cause (spiritually) painful vibrations as the clutch tries to engage. The 23t I have on there now causes vibrations too, but they aren't too bad if I feather and pedal from a stop. I'm going to a 30t there, just to make it even easier on my clutch.
Make sure you replace the stock jackshaft bearings right away, as the casing will shatter under the strength of that motor. Get some super strength sealed bearings. I got some non-industrial heavy duty ones, and they've developed some play after about 80 miles, so I have to replace them now, and upgrade em when the replacements wear out (I still have a spare pair).
This should be a no brainer: do NOT get square edge tires for these things....they make turning so much harder than it needs to be.
I'm going to be using what I learned here to build another 79cc 8 speed. I'll post that one up when it comes. Who knows, maybe this could get a 79cc scarecrow run goin (speakin of, when's the next one? I wanna attend)!
If you are running without the transmission the kit comes with, use a 28t sprocket after the clutch as the bare minimum. Anything less will cause (spiritually) painful vibrations as the clutch tries to engage. The 23t I have on there now causes vibrations too, but they aren't too bad if I feather and pedal from a stop. I'm going to a 30t there, just to make it even easier on my clutch.
Make sure you replace the stock jackshaft bearings right away, as the casing will shatter under the strength of that motor. Get some super strength sealed bearings. I got some non-industrial heavy duty ones, and they've developed some play after about 80 miles, so I have to replace them now, and upgrade em when the replacements wear out (I still have a spare pair).
This should be a no brainer: do NOT get square edge tires for these things....they make turning so much harder than it needs to be.
I'm going to be using what I learned here to build another 79cc 8 speed. I'll post that one up when it comes. Who knows, maybe this could get a 79cc scarecrow run goin (speakin of, when's the next one? I wanna attend)!
I actually don't skip gears at all. The cassette has just the right spread so each shift falls into the powerband, in the lower gears. Above gear 5, it starts falling slightly below, where the engine doesn't have the power to accelerate further. Once I get the 40-11t cassette on there, the spread will be even better, AND I'll have faster acceleration over the 32-11t.
Current spread: 32, 26, 21, 18, 16, 14, 12, 11
Fixed gears: 10t clutch, 23, 9, 48, 36
First gear ratio: 10.903
Future spread: 40t, 34, 28, 24, 20, 16, 13, 11
Fixed gears: 10t clutch, 30, 9, 48, 36
First gear ratio: 17.778
Current spread: 32, 26, 21, 18, 16, 14, 12, 11
Fixed gears: 10t clutch, 23, 9, 48, 36
First gear ratio: 10.903
Future spread: 40t, 34, 28, 24, 20, 16, 13, 11
Fixed gears: 10t clutch, 30, 9, 48, 36
First gear ratio: 17.778
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Experienced bicycle riders avoid severe cross chaining just using leg power so it makes great sense to avoid cross chaining under motor power. Straight chain lines are your friends when biking. 3 or 4 cogs are more chain efficient, two for accelerating and one for running. The cassette stack re-configured with only the preferred ratios and those spaced and shifter adjusted accordingly. Fine tuning with motor sprockets for ultimate performance. Though I've mixed thoughts on which rear cog the "perfectly" straight chain line should be set to, I lean towards running second gear dead straight and thus having low and high gear slightly askance, if three gears are used, my preference...with 4 or more cogs choose your poison.
Having a wide cassette with 6 to 8 cogs works well with 3 cog selections up front on a bicycle, but only if you avoid using ratios that cause wild cross chaining: like running large cogs to large rings or small to small. The angles formed by the chains in these relationships is extreme and put the drive train in stress and promotes increased wear and or breakage to occur.
Moto you made a wise choice in going to three, for riding performance alone. Your also correct when you say we ride differently and I would add to that most don't understand what riding correctly entails.
Rick C.
As a bicycle mechanic, I understand the effects of cross chaining. This is why I center the drive sprocket on the center of the cassette, so it acts more like a 1x mtb system and minimizes cross chaining. I'm now also using an 8 speed E-mtb chain, which can handle that 80Nm of torque the 48v 1000w motors are putting out, which is a level my little 79cc engine could never hope to achieve (it's about 15ft/lbs). And if that isn't enough, I will soon be buying an 8" stainless steel disc to go between my chainrings so my chains do not end up grabbing, and chamfering and polishing the edges so the chains just slip right by.
Chain efficiency is also why I cut out a whole chain, ditching the "transmission" that came with the engine. That's four fewer sources of friction and headache. One less chain, one less shaft, one less sprocket, one less bearing.
I would also like to point out the fact that I have yet to show any signs of excessive wear on my sprockets. The chain broke because it kept binding on the other one, not because it kept being cross chained. The slip disc on my bike is an essential component thus far. I will experiment with chainring spacing and see if that helps.
Yep, I will not be using any chain other than the JT 420 power transfer I've got on my clutch once I get that 250 twin built. There isn't much that can take those 18 horses in the bicycle world. Stuff gets too heavy.
Mtb guys HAVE to get it right and be self sufficient, otherwise they run the risk of not getting back home. Road guys, well, let's say they can get away with having parts break. They can always get a ride back into town or straight to a shop, or they can call an uber home. However, it's still such an inconvenience, roadies do whatever they can to prolong the life of their parts.
That said, I'm taking a more MTB view on this. It's a high strain application, quite synonomous with mountain biking. This is why I keep insisting on the more modern mtb components. Every rock garden mtb wheels go through, the spokes on them easily reach about 5x to 1/5 their normal tension momentarily. They have to be able to handle that time and time again, often, several hundred thousand times. And that's at 14ga. If 12ga spokes were built like that, they'd never break.
I too hope my disc works as planned. I'm really not very keen on having to buy a new chain every three tanks because the things keep binding. Unfortunately, I don't have a hole saw for metal, let alone stainless. Guess I need to get one, along with some carbide drill bits.
Will have to learn allot to make this build work.
Indian22 makes some great points. Pull starting my bike will get old fast. Do not want the lawn mower look or the wear and tear on my shoulder.
The 3d clutch above looks very nice and would fit well with that GTC jackshaft setup MotoMagz is using. That with disc brakes and some paint is basically what I want. Still debating 26x2.5 vs 24x3" wheels.
@ xXNightRiderXx How well were you able to stop with macanical disc brakes? What size disc and tires are you using? How fast is a 79cc predator? What do you think about that exhaust setup? Did you do any other performance upgrades? Any large hills in your area?
Indian22 makes some great points. Pull starting my bike will get old fast. Do not want the lawn mower look or the wear and tear on my shoulder.
The 3d clutch above looks very nice and would fit well with that GTC jackshaft setup MotoMagz is using. That with disc brakes and some paint is basically what I want. Still debating 26x2.5 vs 24x3" wheels.
@ xXNightRiderXx How well were you able to stop with macanical disc brakes? What size disc and tires are you using? How fast is a 79cc predator? What do you think about that exhaust setup? Did you do any other performance upgrades? Any large hills in your area?
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Stopping power is lacking with the mechanical BB7s. 20mph-0 in 50ft with 160mm rotors on 5lb wheels. Now, with the new hybrid hydros, I can stop in 35ft. 180mm rotors with lighter wheels will bring that down to less than 20ft. My tires are 26x2.125. I'm slappin on 2.3s now, without the square edge.
Right now, I'm doin 30mph with the current gearing. I have seen videos of them doin 58mph though. If I reach that, I'll be sure to make a big ol post about it.
This pipe is much too long for this setup, so I'll be trimming it down and installing a 22mm slip on muffler. I do hope it doesn't change the sound too much.
I've lapped my head a bit to remove a gouge from one of the retention pins, but I will be really sanding it down soon. I've also got a Dellorto style carb on a 19mm manifold, matching up the intake, and 18lb valve springs. Come Spring, I'm gonna be sending this engine down to AGK for a billet flywheel, crankshaft, and conrod, and then sending it for sand blasting and powder coating. I gotta have the black with the green frame.
Yes, Boise, sitting right in the middle of a massive riverbed (this river used to be 10 miles wide at least), has some steep, short hills goin up to the benches. Curtis rd has the shortest steep, Protest Rd has the longest steep. Capitol Blvd has the longest moderate.
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Here's a link to the tires I got: https://www.amazon.com/dp/B009NN5GDQ/ref=cm_sw_r_other_apa_i_8bpODbFJ7BNNK
And the chain (which may be a tad too long, so get your breaker ready): https://www.amazon.com/dp/B00SM1OJRO/ref=cm_sw_r_other_apa_i_BepODbDR1M67T
And the chain (which may be a tad too long, so get your breaker ready): https://www.amazon.com/dp/B00SM1OJRO/ref=cm_sw_r_other_apa_i_BepODbDR1M67T
Starting to think 203mm disc may be needed. Looking to max between 40 to 45mph and cruse around 28mph. I think AGK stopped selling the billet flywheel. The fastest 79cc bikes seem to all have the AGK carb or NT carb. Looking at reusing a 2 stroke exhaust pipe with all the insides removed and small adapter to get correct angle.
If you're using mag wheels, then yes, a 180mm rotor will be needed with hydraulic brakes at a minimum to pass inspection (they will ask you to do a brake test).
AGK doesn't sell them individually, but sells them in the stage kits, along with a cam in the stage 2. Stage 1 includes billet flywheel, conrod, carby stuff, and valve springs. Stage 2 includes more carby stuff, and a camshaft, and I think more stuffs. I'm just goin with the Stage 1.
I recommend, for the exhaust, a low profile straight back pipe with a slip on muffler, which can be had pretty cheap. A gutted 2s pipe will be pretty loud.