Big Engine Bicycle 79cc 4-stroke

ZnsaneRyder

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I'm in the process of designing and building a new motored bike.

I want better fuel mileage over 150MPG, and also good low-end torque, and an inexpensive and easy to get engine. I just discovered Harbor Freight has a 2.5HP 79cc 4 stroke, and picked one up. (79 real cc's and bigger than a 2 stroke 80cc)

Engine: http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=97964

I'm putting the engine over the rear tire rack mounted.

It will have a jackshaft and two #40 chains to get the proper reduction.

An issue I'm having is how to get the power to the wheel with a sprocket. I want it to take #40 chain. I don't trust spoked wheels to handle the speed and power, and want to get plastic tuff-wheels, but they don't come in sizes over 24". I see a lot of folks here with chain-driven rack mount setups. What would you recommend?
 

ZnsaneRyder

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I see a lot of folks here with engines over 3HP and driving spoked wheels. Is it worth going to the spoked wheels instead of all the extra hassle of the tuff-wheels and custom sprocket?
 

arceeguy

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I saw those little 2.5 engines at Harbor Freight the other day, and like you, the wheels in my head started turning. A standard 5/8" centrifugal clutch will mount on the output shaft, and with proper reduction this engine will make a nice motorized bike project. The muffler looks like it is a decent size, so it should be a quiet engine. I'm guessing that this is a copy of a Honda utility engine. I already own a few 6.5's built by Lifan or JD, and they have proven to be bulletproof.
 

bikeman6969

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I am in the process of building a 6.5hp bike and i found that the spokes cant handle that so i sent a wheel to the wheelmaster and he put 8 gauge spokes in it for me i hope to have it by monday i also bought a Clam Shell Sprocket Adapter:that i think will do the job but like i said i am running a 6.5 hp so maybe with a heavy duty rim and a Clam Shell Sprocket Adapter i think you will be alright
craig
 

ZnsaneRyder

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I may have to talk to wheelmaster to see what he can do with a spoked wheel.........

Also, I found Staton has a 24" plastic rear wheel with both left and right hand threaded hubs. http://www.staton-inc.com/Details.asp?ProductID=3191
I'd love to get one of those, but I'm not sure how to get a larger sprocket (44T or so) on that wheel, since they only sell a 16 tooth LEFT HAND thread freewheel that fits it.

Also there are 24" tuff-wheels available, but kings sales & service (or anyone else) does not have a sprocket to fit the left side of the wheel.

I'd like wheels similar to this bike on YouTube:
http://www.youtube.com/watch?v=Sv4U_RVVMvg

I really would prefer a working Plastic wheel and sprocket. From experience with a friend's tricycle, a plastic bike wheel can handle over 6.5HP easily. However, I'd still be pleased with a good 26" spoked wheel and sprocket as well.

***In case you are wondering about my drive-gearing before suggesting a wheel solution***
I already have a 10-tooth clutch for 40/41 chain and plan to drive a 30T sprocket for the jackshaft, then have 14T from the jackshaft to a 44T rear wheel sprocket. I have no problem with changing planned sprocket sizes if necessary, but my clutch stays 10T.

1st reduction 10-30T = 3:1 (clutch to jackshaft)
2nd reduction 14-44T = 3.14:1 (jackshaft to wheel)
Total reduction = 9.42:1 or about est 30MPH @ 3600RPM with 26" wheel
 
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fetor56

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I am in the process of building a 6.5hp bike and i found that the spokes cant handle that so i sent a wheel to the wheelmaster and he put 8 gauge spokes in it for me i hope to have it by monday i also bought a Clam Shell Sprocket Adapter:that i think will do the job but like i said i am running a 6.5 hp so maybe with a heavy duty rim and a Clam Shell Sprocket Adapter i think you will be alright
craig
I've also bought a Clam Shell but it's going to be awhile till by build is finished.....if u get to use yours before me can u post your thoughts.
 

arceeguy

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On a whim, I picked up one of the engines today.
It rang up at $89!!

It is not a Lifan, or JiangDong - but a "YonKang Apollo Motive Force Industrial" brand. It does have EPA/CARB certs, with a conformance label. It looks like a Honda GX120 clone, except it is 79cc vs. 118cc and 2.5 vs. 3.5 HP. The castings look to be of high quality - much better than any HT engine! This is why I think the HT engines can be much better, and cheaper too. If Harbor Freight can retail this 4 cycle engine for $89 - a high quality 2 stroke HT engine can be produced for around the same price IMO.

Time to get the welder out and fashion a rack with jackshaft!
zinsane - looks like your sprocket calculations fit the bill - 30mph at 3600 seem reasonable. This would mean 20mph RPM would be low, and quiet so it wouldn't draw unwanted attention. Too bad they don't make torq-a-verters for engines with 5/8" shafts...........

What we need to do is convince Harbor Freight to import a container load of GXH-50 clones, and sell them for $79.95.
 

ZnsaneRyder

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On a whim, I picked up one of the engines today.

What we need to do is convince Harbor Freight to import a container load of GXH-50 clones, and sell them for $79.95.

I agree there! That would be nice to have a small, 50cc, lightweight, blue engine that would fit a larger majority of motored bikes.

Wow, my engine in store was 10$ more than the web price for me - $109.99. Did you get your engine on sale? That's sweet!

As far as the wheel....
I'm pretty sure I want the 24" plastic wheel and the 44T freewheel sprocket. That would be perfect for my setup. Only wondering if the two are compatible, that's the catch. I want a reliable chain drive for this engine, and a freewheel would be nice.
 
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arceeguy

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I took the display model. I got the box and instructions though.
I don't know if they gave me a discount because it was the display unit, I was expecting to pay $99. I've paid $99 for the larger 6.5 engines with a coupon, but this 2.5 is just small enough to fit on a rack and not look ridiculously large. The cylinder is canted the "wrong" way, but you can't really tell with the fuel tank, muffler and air filter hiding the cylinder orientation. I threw some oil and fuel in, and it started up on the second pull. It is a very quiet little engine! I had to choke it to shut it off because I couldn't find the ignition switch. (behind the pull start handle)

I will do without the freewheel because of budget limitations. I don't intend to be pedaling, and even without a freewheel, pedaling shouldn't be much more difficult spinning the jackshaft and clutch bell. I am going to use a HT sprocket with the"rag joint" mount, and hope that the engine doesn't have enough torque to break spokes. If it does, then I'll re-spoke with heavier gauge spokes.

I love my HT (500+ miles), but it is a bit noisy because of the cheap exhaust. This new setup will make less noise and less pollution, and the best part is that it was not a kit - the DIY aspect is what got me into this hobby to begin with. But then again, I still haven't finished my original TLE43/CVT rack mount concept. Winter is here, just need to buy propane to heat the workshop!
 
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