49cc CAG on a 1980 Schwinn - Pocket Bike Forum - Mini Bikes
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post #1 of 29 (permalink) Old 02-19-2019 Thread Starter
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49cc CAG on a 1980 Schwinn

I wrote a coupla introductory posts awhile ago but never saw them posted. So I'll try again.

The shiny object I'm currently obsessed with is in the title above and picture below. The stark simplicity of that silhouette reminds me of board track racers from a hundred years ago. They were the bare essentials. A motor and 2 wheels. Nothing extra. But hey, what else do you need?

The burning question at the moment is gearing. One revolution of the back tire results in 7 ft of forward travel so we're gonna need a lot of reduction. Doing the math, 32:1 indicates 15mph at 6,000 rpm. Does that seem reasonable?
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post #2 of 29 (permalink) Old 02-19-2019
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Re: 49cc CAG on a 1980 Schwinn

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Originally Posted by pntrbl View Post
I wrote a coupla introductory posts awhile ago but never saw them posted. So I'll try again.

The shiny object I'm currently obsessed with is in the title above and picture below. The stark simplicity of that silhouette reminds me of board track racers from a hundred years ago. They were the bare essentials. A motor and 2 wheels. Nothing extra. But hey, what else do you need?

The burning question at the moment is gearing. One revolution of the back tire results in 7 ft of forward travel so we're gonna need a lot of reduction. Doing the math, 32:1 indicates 15mph at 6,000 rpm. Does that seem reasonable?
Sounds kinda feasable but you have to take into consideration that the pedal arms adds fulcrum to the equation..Im thinking without going into mathematics youre gonna have a 5-6mph torque monster on your hands...

Pedal bikes differ slightly from motor bikes as the motorbike has the smaller sprocket on the drive side and a larger sprocket on the power[pedal] side no matter the size of wheel and the bicycle has a large power sprocket and a smaller drive sprocket...Typically theyre geared 2:1/3:1 with even with 26" tires as the length of the crank arms determines things too..

This is known as gain ratio and is alot more accurate to getting a proper ratio for your bicycle.Gain Ratio, which is a calculation that utilizes gear inches and also figures in crank length, since crank length affects leverage.

Almost anything thats motorized has a rule of thumb should be geared between 10-12:1..That should produce enough engine torque to get the bike up to 28-30mph.

For that bike if you plan on using the original crank n chain system and running a sprocket off the leftside front of the crank youre gonna need a sprocket same size as the one thats already on it..

If you do plan on keeping the pedal system too just know on a fixed bike it will be very laborious trying to pedal it on anything but a flat or downhill surface too..Mountainbikes make better candidates for dual moders..

If youre keeping the pedal mode and are adding a rear gear finding a #25 or TF-8mm sprocket or even a #415 chain pinion to work with the rear sprockets for motorized bicycles is gonna be your biggest obstacle..

The engine youre using is a clone of the Robin FL-411NB..They used to sell a 50cc 2 stoke DAX bicycle kit that was called a 2 stroke Dax50 I believe so you may be able to find the drive parts you need..

Last one I built had a Techumseh 3hp 2 stroke snowblower engine with a centrifugal Comet clutch that was modified...

My latest Frankenstein build consists of a similar bicycle with an 8hp Military OHV 4 stroke made by the Chrysler Outboard division built in 1952 and has maybe 10hrs of runtime on it despite its appearance...LOL..Its the very first OHV 4 stroke gasoline engines way ahead of Briggs and Honda..Same design was built by the Chrysler Outboard Corp and used by the military from 1952 until 1987...It has an oilpan similar to a car engine and has an oilpump to circulate the oil too..

Its gonna be a military themed single mode motorized version when Im done...Plans are to add fatter tires.

Good Luck with yours.
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post #3 of 29 (permalink) Old 02-19-2019 Thread Starter
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Re: 49cc CAG on a 1980 Schwinn

Thanx for the response CAM. I'll be using a sprocket on the rear wheel and a jackshaft somewhere in the middle. T8F on the front chain and 415 on the rear sounds like the way to go.

Good tip on DAX too. Another source always helps.
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post #4 of 29 (permalink) Old 02-19-2019
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Re: 49cc CAG on a 1980 Schwinn

No problem..Have you seen these beltdrive systems?

Theyre for 4 stroke but will bolt up to what you have....





Check this site out............. bicycle engine kit, bike engine, bicycle engine, bicycle motor

This one too... https://shop.umotobikes.com/products...x-transmission



Have fun.

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post #5 of 29 (permalink) Old 02-19-2019 Thread Starter
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Re: 49cc CAG on a 1980 Schwinn

That belt drive did catch my eye at DAX. Hadn't thought about that at all. If a Harley can handle it ...

The other reduction box I already got. It was on the motor. But at 8 to 26 teeth it's only 3.25:1 and I'm thinking that's not enough reduction.

Here's my math.

7ft at a time for a mile is 5280/7=754 turns of the wheel.

15mph is 15x754=11,314 turns in an hour.

Divide by 60 minutes and we get 188 rpm at the back axle.

6000rpm divided by 188rpm equals 31.9.

Which is why I ruled out the 3 to 1 box. I'd need 10 to 1 in the back and the smallest 415 gear that seems to be geometrically possible is 8 teeth. An 80 tooth rear sprocket doesn't seem to be available, and if it was it'd be half the size of the wheel! Ouch.

I have seen a 5 to 1 box on the net but just eyeballing it online it looks a bit wide for a bicycle. So I'm thinking a jackshaft is the best answer.

What I didn't know was if 6000rpm was a reasonable number and if you think that's feasible I'm gonna be good to go at 32:1. With a jackshaft I'll be able to play games either way anyway.

And Thank You for your time. I don't know much about these little motors and having someone with your level of expertise is to ask is priceless.
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post #6 of 29 (permalink) Old 02-20-2019 Thread Starter
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Re: 49cc CAG on a 1980 Schwinn

Is a coaster brake sufficient for stopping a motorized bicycle? My guy at the bike shop doesn't think so, but then again, I'm sure he'd like to sell me some discs ...
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post #7 of 29 (permalink) Old 02-20-2019
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Re: 49cc CAG on a 1980 Schwinn

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Is a coaster brake sufficient for stopping a motorized bicycle? My guy at the bike shop doesn't think so, but then again, I'm sure he'd like to sell me some discs ...
Definately not....If you look how one is constructed its housed with-in the hub that also contains grease or has a provision for oil..The hotter it gets the more the hub will expand causing failure within the brake system or the bearings..

At first it will work under normal conditions but when you need it under emergency situations it will break and fail plus again to mention the hotter the hub gets the lesser the brakes will grab effectively..

If you look at the FELT El Guappo bicycle build with the Grubee Skyhawk 66cc 2 stroke kit that bike was a coaster brake model...The new owner had to add a front disc to the front wheel with a cable activated mountainbike brake caliper and clamping action scrub brake friction pads for the rear rim.

Back in the 80's when I used to put methanol burning race kart engines that were chainsaw conversion engines onto Schwinn bikes with coaster brakes I hardly ever burnt out the coaster brake mainly because it also had a scrub rim brake but the spokes never were able to handle the power the engines belted out when they hit the powerband and the rearwheels collapsed fast.......LOL

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post #8 of 29 (permalink) Old 02-20-2019 Thread Starter
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Re: 49cc CAG on a 1980 Schwinn

Thanx CAM! You're indispensable. Back to the drawing board ..... lol.
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post #9 of 29 (permalink) Old 02-20-2019
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Re: 49cc CAG on a 1980 Schwinn

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Thanx CAM! You're indispensable. Back to the drawing board ..... lol.
No shame in unlacing the hub and putting a 70's drum brake in the front wheel like the old schwinn models had....Just adds a lil more to the simplistic route but also adds safety.

Good luck and Youre Welcome plus it was no problem if the info helps..


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post #10 of 29 (permalink) Old 02-21-2019 Thread Starter
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Re: 49cc CAG on a 1980 Schwinn

Where do you come up with that stuff CAM? I was alive in the 70's and I don't remember no stinkin' drum brakes. Where was I? lol. What I do remember is the high bars and banana seats of the first Stingrays. Very popular at the time.


Making progress on a disc setup in that I found a technical drawing of the ISO 6 bolt pattern commonly in use on the rotors. It's a 44mm or 1.75" bolt circle so I'll need a 2" diameter on the hub somewhere.


I also discovered the existence of single speed freewheels! Who knew? We're gonna need one of those to keep the pedals working so that was progress too. The ISO thread on that is 1.375 x 24tpi, and the sprocket looks to be centered, but how wide it is I do not know. Still lookin'.
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i whould just go with a cable disk brake up front off a mt bike

Faster then a speeding E Revo
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Re: 49cc CAG on a 1980 Schwinn

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Where do you come up with that stuff CAM? I was alive in the 70's and I don't remember no stinkin' drum brakes. Where was I? lol. What I do remember is the high bars and banana seats of the first Stingrays. Very popular at the time.


Making progress on a disc setup in that I found a technical drawing of the ISO 6 bolt pattern commonly in use on the rotors. It's a 44mm or 1.75" bolt circle so I'll need a 2" diameter on the hub somewhere.


I also discovered the existence of single speed freewheels! Who knew? We're gonna need one of those to keep the pedals working so that was progress too. The ISO thread on that is 1.375 x 24tpi, and the sprocket looks to be centered, but how wide it is I do not know. Still lookin'.
I have good friends that know I like turning junk into projects,,The Schwinn Cottonpicker I ran across on pure luck chance..I was driving down the road and out of the corner of my eye saw a guy lugging it to the street...I quickly went around the block and quickly grabbed it up and chucked it in my pickup truck..

As far as the freewheels...Yeah they have single freewheel sprockets..The kids BMX bikes come with them and theres some bike manufacturers that make newer single drive cruiser bikes with front and rear scrub or disc brakes so naturally it would have a freewheel sprocket.


When I was a kid my first bicycle I ever had was an old late 60's early 70's Ross Apollo bike with a 3 speed twist grip shifter given to me by a fathers friend who at the time was a garbage man....LOL…The Ross Apollo model was competition to the Schwinn Cottonpicker.

I had this exact model but mine didn't look this good...LOL


It had a single drive sprocket that was freewheel...And yes I did mention that it was a 3 speed and it was...

Coming out of the center of the axle on one side was a very teeny tiney looking bike chain that activated the gear change within the hub.....

They also had another type 3 speed aswell as a 5 speed with floor shifter but it was a cassette style.....

This style inner planetary variable ratio gear freewheel hub design was way ahead of its time...



Keep up the good work and keep us posted..

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post #13 of 29 (permalink) Old 02-21-2019 Thread Starter
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Re: 49cc CAG on a 1980 Schwinn

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i whould just go with a cable disk brake up front off a mt bike
I've had that thought. I could do stoppies. Or get thrown over the bars!

I might have this figured out. The overall hub width will have to symmetrically grow by 5/8". My rear fork springs out more than enough to accommodate this.


The chainline to the freewheel would be outboard by an 1/8" from where it was but that's livable.


Here's a drawing. Not pro. Just for personal use. It makes sense to me and hopefully will to you too!
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post #14 of 29 (permalink) Old 02-21-2019 Thread Starter
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Re: 49cc CAG on a 1980 Schwinn

Better image?



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i run cable disks on my downhill mt bike they have really good control

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Re: 49cc CAG on a 1980 Schwinn

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Better image?



Aslong as its doable to plan you should be descent ..

It kinda looks like you are gonna have to spread the forks pretty wide and add spacers to accomodate for the extra width of your brake idea to keep it symmetrical with the front tire down the center but not disasterous if it doesn't have to be spread wider than the axle will allow..

Theres lots of types of cable disc brake calipers of different sizes/widths and the way theyre mounted...The caliper is whats gonna make the real difference in the mod...

Donor bikes off of craigslist or letgo sometimes make good...…..

Before they changed the laws about the chain of command concerning scrap metal i was able to take anything I wanted off the pile and toss it in my truck when I was bringing a load in to discard...Not anymore

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post #17 of 29 (permalink) Old 02-24-2019 Thread Starter
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Re: 49cc CAG on a 1980 Schwinn

Here's a lovely piece of scrap.





I cut the dia that needs threads for the freewheel .100 too small. Otherwise known as a 1-turn error.
If my foot would reach ....
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Re: 49cc CAG on a 1980 Schwinn

Oops, That's what I hate about lathes, if you move the knob to move the cutter in .001" it takes off .002".
What kind of threads do you need, left hand, and what size & pitch are the threads?? Maybe something that will fit over the undersized section, even if you have to modify what you have to make it work, even epoxy, or something you have force on. CAM2 might be able to help you with that.

Empty Pockets Racing: The difficult we do, the impossible takes longer.....
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post #19 of 29 (permalink) Old 02-24-2019 Thread Starter
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Re: 49cc CAG on a 1980 Schwinn

It's all good. I'll start over. Which is something I do all the time anyway! lol. Ain't got enough sense to know when to quit.

A fresh piece of metal will be here Tuesday and until then I'll continue torturing this one. There's a lotta plunge cutting in between the spoke flanges and I'd like to leave some fat radii in the corners so some experimentation won't hurt.

To answer your thread questions it seems 1 5/16 x 24 tpi is the industry standard for freewheels. That'd be RH threads because pedaling will only make it tighter.

The next dia is to mount a disc brake hub I haven't made yet, and that has to be LH because grabbing the brakes would want to twist a RH thread off. I'll make it 24 tpi too on a 1 1/8 dia.

I'll get it right next time.

Last edited by pntrbl; 02-24-2019 at 11:26 PM.
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Re: 49cc CAG on a 1980 Schwinn

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It's all good. I'll start over. Which is something I do all the time anyway! lol. Ain't got enough sense to know when to quit.

A fresh piece of metal will be here Tuesday and until then I'll continue torturing this one. There's a lotta plunge cutting in between the spoke flanges and I'd like to leave some fat radii in the corners so some experimentation won't hurt.

To answer your thread questions it seems 1 5/16 x 24 tpi is the industry standard for freewheels. That'd be RH threads because pedaling will only make it tighter.

The next dia is to mount a disc brake hub I haven't made yet, and that has to be LH because grabbing the brakes would want to twist a RH thread off. I'll make it 24 tpi too on a 1 1/8 dia.

I'll get it right next time.
It happens to me sometimes too...But there are always saving graces in some muck-ups...….
https://www.amazon.com/SENQI-Freewhe...A22F92YCD7BP3J


Disc brake hubs come in 34mm ,44mm and 48mm sizes...….Freewheel hubs come metric too...

Good Luck

https://www.ebay.com/itm/183123440675

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Last edited by CAM2; 02-25-2019 at 09:46 AM.
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