Big Engine Bicycle 79cc 4-stroke

Discussion in '4-Stroke Engines' started by ZnsaneRyder, Nov 13, 2008.

  1. ZnsaneRyder

    ZnsaneRyder Member

    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)


    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?

  2. ZnsaneRyder

    ZnsaneRyder Member

    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?
  3. arceeguy

    arceeguy Active Member

    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.
  4. bikeman6969

    bikeman6969 Member

    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
  5. ZnsaneRyder

    ZnsaneRyder Member

    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.
    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:

    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
    Last edited: Nov 17, 2008
  6. fetor56

    fetor56 Guest

    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.
  7. ZnsaneRyder

    ZnsaneRyder Member

  8. arceeguy

    arceeguy Active Member

    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.
  9. ZnsaneRyder

    ZnsaneRyder Member

    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.
    Last edited: Nov 17, 2008
  10. arceeguy

    arceeguy Active Member

    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!
  11. xPosTech

    xPosTech Member

    Not a spoke breaker

    There's a reason spokes break. They're not tight enough. At least with multi-speed freewheels the left side spokes aren't tight enough. They're that way on purpose.

    Grab two left side spokes. Feel the tension. Now grab two right side and feel the tension. The right side spokes are really tight to pull the hub to the left/pull the rim to the right in order to center the rim and allow room for the cogs on the freewheel.

    The more sprockets (cogs) on the freewheel (or freehub in the case of 7, 8, 9 speed and above) the more the wheel is dished. I would never go over 6 cogs. 5 is much better for our purpose. I tighten up the spokes on the left side as much as I can without altering the dish too much.

    Also, check the spacers/locknuts on the axle. Sometimes you can put thinner spacers and/or locknuts to give you some room to lessen the dish. You might have to add spacing to one side or the other. You might have to run the rim a smidgen closer to the left side stays.

    I run at least 36 spoke wheels, the bigger the spokes the better. At least cross 3, with cross 4 being better.

    Learn to true your own wheels. It's not hard and can be done on the bike if you're lazy and don't want to put the wheels on a stand. It's much easier to keep one true than to true it up after it becomes wobbly. But even that isn't hard.

    Just do whatever you can to lessen dish and tighten left side spokes.

    If you haven't yet signed up for Harbor Freight's email list/Preferred Customer List. Print the coupons and save. Also all you have to do is ask "Can I get this for the online price?" (which you already checked, right?) and they happily sell it to you for that.

    If I had to get a job :)wheelchair:) I'd try to get hired at HF. Just think - an employee discount, too.:clap:

  12. xPosTech

    xPosTech Member

    One more thing to stop breaking spokes. The last thing I did.

    I ordered a shift kit from Pablo.:shifty2:

  13. 5-7HEAVEN

    5-7HEAVEN Guest

    "Also, I found Staton has a 24" plastic rear wheel with both left and right hand threaded hubs.
    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."

    Staton has a 24-tooth A-type sprocket with left-hand threads to fit their left-side hub. It threads on, but with no freewheel. With a centrifugal clutch, the engine won't mind, but all chain and sprockets will be spinning while coasting.

    If Staton can thread a 24-tooth A-type sprocket with left-hand threads, then ANY sprocket with enough meat can be machined with left-hand threads. Ya just have to find the machinist to do it, or ask Staton if he could do it for you.
  14. arceeguy

    arceeguy Active Member

    BTW - just got a HFT flyer today and the 2.5 OHV engine is "on sale" for $89 - reg price $109 until 12/23/08. So I paid the sale price with no discount for buying the display unit.
  15. Plastic wheels are fairly durable, the only negetive thing I have to say about them is they don't like hot sunny days, if they sit for any period of time in direct sun on a day that is even slightly warm, you come back to a bike with warped wheels and your brakes rub, the only way to fix them is to find a freezer big enough and put them in overnight, then hope they remember where they were prior to the exposure, the lighter colors like white or yellow don't warp as quick, but they still warp ! black is terrible. I think Andy Inchville has the answer to the Hub/Thread problem, you might PM him and see what he say's ?
  16. ZnsaneRyder

    ZnsaneRyder Member

    I'll PM andy again. He said there was no sprockets he had to fit the wheel, but maybe he knows if the 44T or 48T freewheel from bicycle engines will fit. I figured it's a freewheel made for their special two-side hubs for spoke wheels, so it hopefully fits the staton hub as well. I'm pretty sure being only a 3600RPM engine, that the 80CC is more likely to break stuff than a smaller Honda50, so I want to be sure I have overkill for my rim.

    Also, I'm really looking forward to a freewheel if possible because I plan on pedaling a LOT, but want the option of having the motor as well.
  17. jk-1

    jk-1 Guest

    Hello , I just went by my local HF and they have one 2.5 hp engine in stock, I almost bought it But I wanted to ask you guy's first about the size of the engine, Is it small enough to put into the frame of a bike, Whizzer style ?

    Thanks Jim
  18. arceeguy

    arceeguy Active Member

    The 2.5 is too large to fit in the V of the frame.

    IMO, it is almost too large for a rack mount. It has the same size frame as a Honda GX120 series 118cc engine, and it weighs over 20 lbs. Also consider the weight of a clutch, jackshaft, and rack - which isn't trivial.

    The little Honda GXH-50 and "clones" are the perfect size (and have legal cylinder displacement) for MB projects, but you can't by them for $89 at Harbor Freight. It's the low cost for a horizontal shaft 4 stroke that makes this a good find.
  19. jk-1

    jk-1 Guest

    Thank You Arceeguy for the information. Take Care Jim
  20. arceeguy

    arceeguy Active Member

    No problem!

    Even if you strip off the stock muffler and fuel tank - the cylinder will still be canted the wrong direction unless you find a gear reduction box to reverse the CCW rotation of the shaft.

    Rack mounting or a pusher trailer would be best for this little engine.