Can a small motor ~30cc power a heavy dude?

motoringbike

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Jan 28, 2014
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I am just wondering if I got a total bike + rider weight of 350lbs, can a small 33cc motor with the right gearing actually work?

I am thinking of doing a hybrid electric hub motor along with a ICE motor for long stretches of road. I would have to use google maps to find out the grade, but 5% tops. For in the city that would last for 100m, but on the highway, 1 mile or so.
 

5-7HEAVEN

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Aug 2, 2008
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I think so, especially if you're pedaling with an electric hub.

Don't expect to go 35mph.

Use a shift kit with the engine and gear the 8-speed cassette super low.

You'll have to convert to 78mm clutch, in order to use either the pocket bike 5:1 transmission, or the pocket bike CVT transmission.

Using this clutch adaptor:
http://www.staton-inc.com/store/index.php?p=product&id=875

Try to get 1st gear 46:1 or lower. Highway gear will then be 15:1.
Since you only have a 1-mile highway, you can gear it even stiffer.

Choose the correct chainring to help pedal.

This will take some engineering to gear this engine, or any engine, for that matter.

You could use rear friction drive, but you wouldn't have the gearing.

This might be the perfect engine for your needs. It's 22cc, quality 1.3hp Tanaka engine. The price is awesome too:

http://www.ebay.com/itm/TANAKA-Util...ash=item440023f0b6:g:G7YAAOSw9k5XPnI8&vxp=mtr

FWIW, my bike and I weigh almost 300lbs. With 47cc and gearing, it works very well for me, hills and flats.

However, if I were me, I'd choose a 35cc-up engine which uses the larger 76mm clutch. Then, no expensive adaptor and additional clutch parts.

You'll need the 76mm clutch to bolt on the pocket bikes' 5:1 transmission or 7:1 CVT trans. That's the only way to utilize low gearing and high gearing.
 
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crassius

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at best, you'll get some pedal assist help on flats, but here where we have huge hills, they won't quite get you up a big hill even when pedaling (you'll end up stalling the motor by being too slow)
 

5-7HEAVEN

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at best, you'll get some pedal assist help on flats, but here where we have huge hills, they won't quite get you up a big hill even when pedaling (you'll end up stalling the motor by being too slow)
With 46:1 low gear, it's like having a 111-tooth rear wheel sprocket pulling you. That, plus an electric hub AND pedaling will get any person up steep hills. Maybe at jogging speed. Anyway, the OP only has inclines of "5% tops".
 
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crassius

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yeah, for some folks it works - I can not pedal more than 1/2 a block, so when I've ridden those, I've gotten stuck and had to walk the bike out
 

motoringbike

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I should clarify, the gas motor will be used alone and not with the battery.
Also I decided to go with a motorized pusher trailer for the gas motor.
If that be the case I need to see the difference in physical size from a 30cc to a 50cc to a 65cc then 2 stroke vs 4 stroke.

What is the average price to pay for these engines?
 
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motoringbike

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Oh I doubt I will be buying online, I figure I will buy from Princess Auto here in Canada, its like your American Harbor Freight. They sell Power Fist which are Honda clones I believe.

https://www.princessauto.com/en/search?Ns=sku.price_listPrices|1&Ntt=engine&No=0&Nrpp=48

Here is a quick rundown
79cc $149
180cc $170
173cc and the 140cc are verticle shaft $150
196cc $189
208cc $199
208cc with elec start $299

So with my first gas power bicycle being a pusher trailer, I believe I can go larger engine, as the price is all under $200 from 208cc down to 180cc. But for later to mount inside the bike frame will be a real p.i.t.a.
 

5-7HEAVEN

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Wow! From a mini-30cc, you're now shopping for 200-plus cc's!
If this is your first build.....be careful!

You could start with a 49cc pocket bike engine. They're easy to mount and provide good power, when properly geared.

My engine has 47cc and pulls me along just fine.
 
Jan 21, 2015
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Portland, Oregon
Oh I doubt I will be buying online, I figure I will buy from Princess Auto here in Canada, its like your American Harbor Freight. They sell Power Fist which are Honda clones I believe.

https://www.princessauto.com/en/search?Ns=sku.price_listPrices|1&Ntt=engine&No=0&Nrpp=48

Here is a quick rundown
79cc $149
180cc $170
173cc and the 140cc are verticle shaft $150
196cc $189
208cc $199
208cc with elec start $299

So with my first gas power bicycle being a pusher trailer, I believe I can go larger engine, as the price is all under $200 from 208cc down to 180cc. But for later to mount inside the bike frame will be a real p.i.t.a.
You're forgetting to include the cost of all the parts you'll have to buy to make those engines compatable with a bicycle. The kit engines have internal gear reduction and a built in clutch, whereas you'll have to make your own for any of those engines. Add in mounting hardware, throttle linkage, exhaust pipe, gas tank, etc, and you'll be spending a lot more than $200. If you want an idea of what you'll be getting into, and if you want an easier time if you do decide to go that route, I made instructions for how to build a bike using the 79cc predator engine, which can be found here: http://www.instructables.com/id/79cc-Motorized-Bicycle-From-Scratch/
 

motoringbike

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I never realized that. The Princess Auto 79cc has throttle linkage.
79cc looked good, but now you say buy a kit. Which of the countless kit companies are Canadian?
 
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Jan 21, 2015
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I never realized that. The Princess Auto 79cc has throttle linkage.
79cc looked good, but now you say buy a kit. Which of the countless kit companies are Canadian?
I'm not necessarily saying buy a kit. I despise kit engines and only build from them if my customers are on a tight budget. I'm saying that you will have to spend more than you thought to do it right. And the throttle linkage will have to be changed if you want to use a twist throttle on it.
 

Dave31

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Mar 1, 2008
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Not a heavy guy but my 31cc Zooma did well on the Junk Yard Dog. I ran a 36T sprocket and could reach up to the 30's on flat land.

I will admit it was gutless and had to do a little pedaling to maintain a constant speed on hills or a good head wind but for the most part it did very well.
 

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Agreen

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When I was around 200-210, I used a weed eater 20cc as a friction drive. It was about the most ghetto thing I've ever ridden, but it did the job. I zoomed around the neighborhood for a while before taking it out to actual roads. I had to assist it to top speed by pedaling, but it could maintain a solid 20-25 mph on flat ground. If a 20cc weed eater can do that, I'm sure a 33cc could do at least 50% better, right? Add another 50% of my weight, assuming the bike and motor weigh comparably, and you should expect similar results as me.
 

5-7HEAVEN

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Not a heavy guy but my 31cc Zooma did well on the Junk Yard Dog. I ran a 36T sprocket and could reach up to the 30's on flat land.

I will admit it was gutless and had to do a little pedaling to maintain a constant speed on hills or a good head wind but for the most part it did very well.
To convert a gutless wonder to a hill climbing marvel takes a bit of leverage.

As Archimedes once said, "Give me a big enough lever and a fulcrum, and I will move the world".

Small engines LOVE low gearing aka leverage. A mechanical advantage of 40-50:1 gearing does wonders climbing steep inclines. On my bike, Snow Tiger, I can go from walking speed at the base of any hill to its crest in short order. That's with 35.51:1, akin to having a 87-tooth rear wheel sprocket.

The OP might want to start his project with a cheap 49cc pocket bike engine, instead of 30cc or 208cc engines. Bolt it onto a trailer or above the rear wheel. Gear it at 20:1 to max out at 8,000rpm. Install the pocket bike 5:1 transmission. Use an 11-tooth drive sprocket and a 44t wheel sprocket. Low end crawling should be good, as well as mid and 30mph top end speed..weld
 
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motoringbike

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I am going on a long trip, so I think I want to buy the Princess Auto 79cc its rated for 3HP at 3600RPM, so I need to also buy a 72T #35 and a 10T #35 along with the #35 chain, to get a 7:1 ratio which puts it at 500rpm, in either a 20" --> 29" wheel, I have a Sturmey Archer 3 gear IGH in a 26" rim, I think that is ideal dont you guys?

The Sturmey Archer will easily take 2200W of power, easy.

All I need now is to find a 5/8 clutch as Princess Auto does not sell them, do I just go to a motorcycle store in town for that?
 

5-7HEAVEN

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So you're putting this engine on a push trailer, correct?

I'm curious to see how you're going to hook up the 72t sprocket to the right side of the 3-speed hub.

.trlrl.
 
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Jan 21, 2015
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Portland, Oregon
I am going on a long trip, so I think I want to buy the Princess Auto 79cc its rated for 3HP at 3600RPM, so I need to also buy a 72T #35 and a 10T #35 along with the #35 chain, to get a 7:1 ratio which puts it at 500rpm, in either a 20" --> 29" wheel, I have a Sturmey Archer 3 gear IGH in a 26" rim, I think that is ideal dont you guys?

The Sturmey Archer will easily take 2200W of power, easy.

All I need now is to find a 5/8 clutch as Princess Auto does not sell them, do I just go to a motorcycle store in town for that?
7:1 ratio is way too steep for a 79cc. You wouldn't even move. I run 13:1 and I'm only 155 lbs, and on very steep hills I still have to pedal assist a little bit. Also you'll want to remove the governor system and you'll be able to turn 6000 rpm, otherwise you'll be really slow. Here's a 5/8" #35 clutch: http://www.bmikarts.com/Max-Torque-Clutch-35-58-Bore-_p_723.html BTW, I compared the princess auto vs the harbor freight 79cc and they are almost exact duplicates of one another, except that the princess auto costs $50 more.
 
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