Will this cheap CVT fit this cheap engine?

[MrDoboz]

And is it even a good idea?
Sorry in advance for maybe being stupid, I'm a total noob in the field, this is gonna be my first build.
So I ordered this 49cc 2T Samger pocket bike engine ($60 from Ali) and planning to put it on a 4x26" fatbike. I live in a quite hilly place so I won't even be able to get home without a really slow gearing, and that's not fun. I figured I'll go for some kind of cvt or other way of changing gear ratio if there is one (except for jackshift derailer setup, that sounds rather weak and dangerous). Also I'm gonna get rid of the pedal drivetrain as it's useless, the hill I live on top of is so steep and rolling resistance of the fat tire is so bad, I can't even pedal up with a gear ratio of 28-32 (chainring-sprocket). Also my budget is rather limited, my supply options is Ali and eBay with free shipping, my tool park is lacking, and I have no idea why I even ordered the engine, so that's my story in short.
so what do you think? can I pull this off? or you have other suggessions of what I should do in a similar price range (this CVT is $70 also on Ali)?
Thanks for any input and sorry for the rambling

 

[Gordy]

Keep the pedals to assist the engine up a hill. That engine likely won't make it by itself. @Sidewinder Jerry lives in the mountains and has a very unique setup with the widest gear ratio reduction. He runs a derailleur shift setup and has for a very long time.

 

[Sidewinder Jerry]

And is it even a good idea?
Sorry in advance for maybe being stupid, I'm a total noob in the field, this is gonna be my first build.
So I ordered this 49cc 2T Samger pocket bike engine ($60 from Ali) and planning to put it on a 4x26" fatbike. I live in a quite hilly place so I won't even be able to get home without a really slow gearing, and that's not fun. I figured I'll go for some kind of cvt or other way of changing gear ratio if there is one (except for jackshift derailer setup, that sounds rather weak and dangerous). Also I'm gonna get rid of the pedal drivetrain as it's useless, the hill I live on top of is so steep and rolling resistance of the fat tire is so bad, I can't even pedal up with a gear ratio of 28-32 (chainring-sprocket). Also my budget is rather limited, my supply options is Ali and eBay with free shipping, my tool park is lacking, and I have no idea why I even ordered the engine, so that's my story in short.
so what do you think? can I pull this off? or you have other suggessions of what I should do in a similar price range (this CVT is $70 also on Ali)?
Thanks for any input and sorry for the rambling

Let's first answer your question and the answer for what you're suggesting is NO it isn't going to work. The steepest paved streets in the world are a 37% grade. Where I live 30% grades are common. The 3 determining factors for ratio reductions is:
Grade %, Total Weight, and Engine Power.

Unless you plan to ride in the snow I suggest switching out the fat tires to 2" wide road slick tires.

Here are specs on your 49cc 2 stroke engine:

Max rpm~11,000
Idle rpm~2,800
Max Torque rpm~5000 (1.6 ft/lbs)
Max Power rpm~6500 (2 horsepower)

So depending on total weight and grade% you're going to need a reduction somewhere between 40\1~50\1. Granted this isn't going to give you very much level ground speed. Which is why small engines in mountainous regions need multiple engine driven gears.

The good news is: I can tell you how to build such a bike using the engine you have. The bad news is: this build won't be cheap. You either need a much bigger engine or buy a manufactured bike capable of climbing the hills.

 

[cloakedvillain]

While it is possible to make that work it would be a nightmare of belts and chains. Staton inc sells clutch bells with a 1/2 inch keyed shaft, but its too short and too skinny for that cvt.

 

[Sidewinder Jerry]

While it is possible to make that work it would be a nightmare of belts and chains. Staton inc sells clutch bells with a 1/2 inch keyed shaft, but its too short and too skinny for that cvt.

The minimum reduction would have to be around 16\1. Meaning you'd need a 10t/160t sprockets for a reduction range of 48\1~16\1. The only way around that would be to create another reduction point: cvt to dual sprocket jackshaft to rear wheel. Which isn't going to be easy to do with the limited space due to using fat tires.

CVT's can also have slippage issues when climbing extremely steep hills.

 

[MrDoboz]

Keep the pedals to assist the engine up a hill. That engine likely won't make it by itself.

yeah, I see what you're saying, however the current pedal drivetrain is trash, both derailers worn out, hanger bent, shifters old and integrated with the brake levers. I'm planning on installing those cheap $30 light control handlebar switches and then I either can't reach the buttons (horn, turn signal, etc.), or the brakes, so this setup has to go. Also front derailer will very likely not fit with the engine. neither the crank arms lol. I will keep in mind the option to later put on some pedals to do something, but it will be an expense to be even remotely useful.

So depending on total weight and grade% you're going to need a reduction somewhere between 40\1~50\1. Granted this isn't going to give you very much level ground speed. Which is why small engines in mountainous regions need multiple engine driven gears.

I've run some math on this. By the numbers I find online, the CVT should have around a 300% range. If I use 40:1 for top "gear" I get just below 20mph@9000rpm. I don't think I want too much more just yet. That said, this would mean 120:1 bottom "gear", and that is 3.5mph@5000rpm. These hills here are not too extreme, 10-15%, it's just the fat tires that put it over my capabilities. I'm let's say 200W, and I can do it at 3mph, so I'm pretty confident the engine should take it just fine. That is, if the 3:1-1:1 range claim is correct and I can gear it 40:1 on top of that.

While it is possible to make that work it would be a nightmare of belts and chains. Staton inc sells clutch bells with a 1/2 inch keyed shaft, but its too short and too skinny for that cvt.

u saying my crankshaft is too short? NOOOOO I don't have a lathe. :c

 

[cloakedvillain]

The crank is fine, its the output that's the problem. I'll draw up what could work after I get home from work.

 

[MrDoboz]

The minimum reduction would have to be around 16\1. Meaning you'd need a 10t/160t sprockets for a reduction range of 48\1~16\1. The only way around that would be to create another reduction point: cvt to dual sprocket jackshaft to rear wheel. Which isn't going to be easy to do with the limited space due to using fat tires.

CVT's can also have slippage issues when climbing extremely steep hills.

This is some very lame, but supposedly to scale mockup. I have some free space, especially if I don't mount the engine like that (vertically, upside down, under the seat)

 

[MrDoboz]

The crank is fine, its the output that's the problem. I'll draw up what could work after I get home from work.

if you mean the cvt output, then yeah it's kinda scary but I want to make it a right side drive, as I don't want to hurt the disc brakes, that means a much longer custom shaft anyways, but I don't think I'll find a 400T wheel sprocket to get the 40:1 baseline lmao. maybe a 10:1 planetary gearbox as a jackshaft? then 4:1 is easy with the chain. idk where I find a planetary gearbox with enough torque tho, I suspect one from a cordless drill won't be enough

 

[Sidewinder Jerry]

yeah, I see what you're saying, however the current pedal drivetrain is trash, both derailers worn out, hanger bent, shifters old and integrated with the brake levers. I'm planning on installing those cheap $30 light control handlebar switches and then I either can't reach the buttons (horn, turn signal, etc.), or the brakes, so this setup has to go. Also front derailer will very likely not fit with the engine. neither the crank arms lol. I will keep in mind the option to later put on some pedals to do something, but it will be an expense to be even remotely useful.


I've run some math on this. By the numbers I find online, the CVT should have around a 300% range. If I use 40:1 for top "gear" I get just below 20mph@9000rpm. I don't think I want too much more just yet. That said, this would mean 120:1 bottom "gear", and that is 3.5mph@5000rpm. These hills here are not too extreme, 10-15%, it's just the fat tires that put it over my capabilities. I'm let's say 200W, and I can do it at 3mph, so I'm pretty confident the engine should take it just fine. That is, if the 3:1-1:1 range claim is correct and I can gear it 40:1 on top of that.



u saying my crankshaft is too short? NOOOOO I don't have a lathe. :c

Generally the lowest your engine can go in reduction is 16\1. With a CVT that'd be 48\1 on the bottom end.

If all you have is 10-15% grade hills I suggest getting a JaiLi double chain reduction box and running a 10t/60t sprocket for a total reduction of 36\1. What is the actual height of your fully inflated tires