New to Motorized Bikes!

Discussion in 'Introduce Yourself' started by TABrinn, Jan 23, 2014.

  1. TABrinn

    TABrinn New Member

    Hello to all! A few weeks ago I came up with the crazy idea to put a Briggs and Stratton lawn mower engine on a bicycle and use it as uber-cheap transportation to work. I can park my truck, cancel its insurance, and get upwards of 100 mpg, if not better for a savings of nearly $200 a month! I wanted the bike to resemble a Board-Track racer from the 20's. I googled to come up with some inspiration and ended up here. Turns out, I'm not quite the pioneer I thought I was. But... there are some truly great builds on here and I look forward to learning and sharing with yall.

    Naturally, I've got some questions. The only part I currently have for the build is the motor, a 4.5 hp Briggs and Stratton engine. I've been researching various performance mods on the Go-Kart forums and figure I can pull about 6000 RPM's. At a 8:1 gear ratio on 26" rims should put me just shy of 60mph. Is this speed safe on a bike frame? Will the frame hold together, welds crack, tires fly apart, etc? Thinking of using moped wheels and tires that should safely handle the speed and give adequate brakes, right? I'd like to keep the pedal drive and figure out how to pedal up to speed, and dump the clutch to start the motor. My commute is 24 miles round trip with stop lights, stop signs, and 1 overpass to climb. I would like some sort of Gear Box (Ride Mower, ATV?) to help with excelleration, climbing the overpass, and down shifting to slow down. I will need head and tail lights, turn signals, horn, etc to pass tech inspection to get onto the base where I work. Look forward to working this out with you guys!

  2. butterbean

    butterbean Well-Known Member

    60 mph is not safe unless you build for it. What I mean is, bicycle tires are rated for 35, 40 max. At 60, you will be leaving a lot of rubber on the road. The tires will get very hot and they won't last long, if at all. If you're not mechanically inclined/experienced, then I don't think this is a good starting project. If you are, then have at it but be careful. 8:1 is not sufficient reduction for 6k rpm's. I run 5.2k tops and I'm geared at 12.44:1, I will redline at 32mph. If you're not taking it on the highway (which is not recommended anyway, in most states you would have to pass a motorcycle inspection to be allowed on the highway anyway), then you don't need to be able to do 60 and you might not have as much torque for hill climbing. 35, 40 mph is plenty fast. At that speed, I still recommend moped or motorcycle tires. If you look around, you may find some 26 x 2 motorcycle tires that will fit a standard bicycle rim. I believe there are also some moped tires that will fit 24" bicycle rims. Yes, moped hubs will have pretty good brakes, most likely drums. I am not sure if the lawnmower engine can easily be adapted to the bike or not, because if it has a vertical crankshaft, it will be much harder to fit a transmission on it. If it has a horizontal crankshaft, you're good to go. But there are also engine kits available, and with a 4 stroke engine and a mountain bike, you can install a shift kit and use the bike's gears as a transmission. The 4 stroke kits are a bit more expensive, but probably cheaper than a non-kit bike. Even with an American made transmission (the 4 stroke kits come with several different transmissions), they are still about $200 less than what I spent on my custom bike (about $800 to get her rolling). I can help you with setting up a battery and charging system for your lighting system, and it's not very expensive (about $75 or less), but I have no experience with turn signals except for the crappy cheap battery operated ones that break very easily. I just use hand signals, not sure if that's an option for you. One piece of advice I can give you. I know you're excited to build your first bike, and that's completely understandable. Take a breath, slow down, take the time to gather all the info you will need (it's going to be quite a bit, if you do build a custom bike it's not going together in an afternoon), and find out what parts you will need, what it will cost, and whether you have the tools and skills needed to build such a beast, then decide if you want to go that route or if getting a kit would be more suitable. If you do decide to go forward with the 4.5 hp engine, build it like you're building a mini-motorcycle, because you pretty much are, and to not build it as safe and reliable as possible is not only risking your life, it's risking others lives and the reputation of this hobby as well. Good luck.
  3. butterbean

    butterbean Well-Known Member

    If you gear for 60mph, you're also going to need hydraulic brakes.
  4. Donavan321

    Donavan321 Member

    Even with hydraulic brakes, I wouldn't want a bearing blowing out at that speed or a hub seizing. You'd be in for it for sure! A front disc would be the best ideal brake to use. 60mph may be fun, but just be very careful! Have any pictures, or have you not started the construction yet?
  5. Fabian

    Fabian Well-Known Member

    If you gear for 60mph you're also going to need good health insurance.
  6. butterbean

    butterbean Well-Known Member

  7. butterbean

    butterbean Well-Known Member

    Oops lol only meant to put that once.
  8. Fabian

    Fabian Well-Known Member

    If you gear for 60mph you're also going to need a high pain threshold.
  9. Fabian

    Fabian Well-Known Member



    Quite likely

    and just shy of a white knuckle flirtation with disaster...

    Only if you are wearing a super hero costume.

    It is not a crazy idea if you don't value you life, however, if you "do" value your life, the idea is complete lunacy!
  10. TABrinn

    TABrinn New Member

    I'm well aware of the potential hazards. I do want to build this properly, strong, safe, reliable, modestly budgeted, and be able to cruise along at least 45mph. Most of my commute is at 45mph but there is a short stretch of 65mph. Riding a motorcycle is dangerous. Riding a home built one is down right suicidal, if not VERY WELL executed. Please don't flame, I'm here to learn all I can from the collective knowledge here. In time I'm sure I will have something of value to contribute. I am an A&P Mechanic by trade but primarily work on Aircraft Electrical and Avionics. I am in the middle of building a 67 Ford Ranch Wagon and a 71 Datsun 240Z. I know Aircraft and cars but my knowledge of Bicycles or Motorcycles is sparse. Both car projects are stalled due to lack of funds and I hoped this would be a fun means of freeing up roughly $200 per month from gas and insurance.
  11. ez dave

    ez dave New Member

    cromo frame good brakes and safety wire. btw 45 on a motorized bike feels much faster, most people dont even want to see 40. keep in mind also power assisted bicycles have a maximum allowed speed of 20 mph, that is a federal law, even though i often break it. when the police ride behind me i just slow down and start pedaling. butterbean has some good advice. what are the laws in tx, just curious.
  12. butterbean

    butterbean Well-Known Member

    Chromoly isn't the only good frame to motorize. American steel if you can find it, and even some department store bikes have solid frames. Not saying the rest of the parts on a department store bike will be solid, but I have a cranbrook frame in my basement that's almost 4 years old, and held my 280 lb butt just fine.
  13. Donavan321

    Donavan321 Member

    Department store frames

    I can AGREE with this statement and back it up. I have used several Huffy bicycles. Cranbrooks, as well as Santa Fe Cruisers. I have not had ONE problem with them breaking down, falling apart, frames cracking, etc. I've used alot of "department store bikes" for my builds since I'm on a REALY tight budget. I ride it until/if it breaks down. At that point, I can get everything I need locally from some local bike guys. A guy I know runs a bike shop and I can get STEEL(usually) complete rims..cassettes and everything included for 10-$15 and he trues them up for a bargain price as well. So, I will continue using department store bikes!
  14. TABrinn

    TABrinn New Member

    I like the look of the Huffy Millennial Cruiser at Walmart. Anyone know if I could order a bare frame? Has enyone experianced frame failure? If we can find the most likely places to crack, gussets could be welded in for additional strength. Some sort of suspension is a must to absorb some of the abuse from the road. I love tho look of the Springer front fork, but also want to work out some rubber bushed motor mounts to absorb vibrations from the engine. Its amazing to think how much vibration stresses, fatigues and eventually leads to structural failure.
  15. butterbean

    butterbean Well-Known Member

    Most times when people try the rubber bushings, it causes more vibration and has actually caused a few frames to crack.
  16. V 35

    V 35 Member

    You are asking a lot ! First off, take a look at the wheels on a $ 100 bike, pay attention to where the rim is seamed, a couple spot welds at best, now consider, you want to operate at about 5 times the rated speed, for long periods of time . Worksman wheels are probably the toughest in the business [ check out a Hot Dog Cart, if you can't find a bike handy ] Some Mountain Bike Wheels are very tough, double wall, 14 GA spokes, but are built for impact resistance, not speed. As for reliability, I figured on starting with a 2 stroke, than gravitate to a four stroke for more reliability.

    From what I've seen, the 2 strokes are actually more durable, and reliable, hard cornering starves engine for oil = short bearing life
    Transmissions seem failure prone, a four stroke has too many jackshafts and other components to be reliable . If the store boughts are short lived, think about how long a cobbled together home made will last. When it comes to engines, at least get a horizontal shaft, a vertical shaft is lunacy. Look at lots of pictures, if cheap is your only goal, buy a used moped. If you want a sweet cruising, reliable bike, be prepared to spend what it takes, and as you know from your other builds, it * can * get expensive . The fact that your an A P means you have an eye for quality, and safety, don't get hurt saving a few bucks, its not worth it.

    Go Fast / Crash Hard
  17. professor

    professor Active Member

    TA, you have gotten real good advise here.
    I think your expectations are out in space.
    The Briggs will not propel you to 60.

    I run a 212cc and it will stay with traffic or just ahead, but I have to work at it and I have 3 gears, moped wheels,and full suspension.
    It is wound out at 4400 rpm and a tad over 40 mph.
    Rarely do I ever do that.
    Set up the way it is - 9 hp is on tap and I cruise around at the motor's sweet spot-25-28 mph.

    Legally- it is a moped.
    Mopeds are for the side of the road and 20 something mph is safer than being IN traffic.

    Your desire requires a real motorcycle- something 175cc and up.

    And I agree, motorcycles are too dangerous BECAUSE you then will be IN traffic.
    The very place you intend to ride?

    Long ago when I rode motorcycles, the temps here in Buffalo would hit 85 or a bit more, and I could not keep from becoming a sweat ball (leather jacket, boots, helmet, always) on a motorcycle, no matter how fast I went.

    Doesn't it hit a hundred often in Texas? Are you sure you want to dump that car?
  18. keatonx

    keatonx Member

    A 212cc preddy should be able to hit 60mph, and a 4.5 briggs should atleast approach.
    I've gone atleast 55 or so on my lawnmower bike, according to an online go cart speed calculator. That's with a 140cc 2 stroke mower engine (stock 4hp but it has some work for sure). But cruising at that speed? Daily? You will die for sure, unless you use a proper motorcycle frame. My lawnmower bike is straight as an arrow at high speed, but I've only taken it that fast once, maybe twice. It's a very sketchy bike, so I rarely ever ride it anyways.

    Converting a vert. Shaft to a horizontal won't be perfect and you'll probably still get some oil starvation. Either way, maintaining 60mph daily with a cheapo briggs will kill the engine within a few weeks probably, unless you gear it so it isn't over-revving so much (anything over 3600 will eventually cause the big end bearing to heat seize, and throw the rod)

    And what about flywheel explosions?? Happens all the time with the racing mower guys; the cheap cast iron flywheels could fly apart and kill you. But since you have a mower engine it'll be an aluminum flywheel, which causes problems of its own. My 2 stroke mower bike has an alum. Flywheel and it runs VERY rough. I once tried
    Starting a 4 stroke briggs 6.5hp without the blade acting as a flywheel and it kicked back almost every pull. It would tear the handle out of my hand and smash it into my ribs painfully hard. Even my lawnmower bike kicks back pretty bad at times; I need to slowly pull it to TDC, then pull it to prevent it from kicking back. (Old powersport trick)
    If you search up "lawn mower blow up" or something like that, there's one video where the guy actually removes the governor so it revs wide open. It threw a rod in a few minutes. So unless our stretch of 65mph highway is 1/2 a km long then you're asking for trouble :jester:

    Also, a stock briggs with no governor will only rev to 5500rpm or so, because the valves start floating.
  19. Donavan321

    Donavan321 Member


    *Really(my mistake) As far as rubber mounts and all that. I've never cracked a huffy frame using a china girl. My fastest bike I built went about 46mph max speed, it was on a cranbrook frame. Rode it like that for a REALLY long time, no blown bearings, no wrecked spokes, etc. Rubber mounts: BAD idea, as mentioned above they cause more vibration and can put more stress on the mounting studs causing them to SNAP off, usually in the block, requiring a drill bit and a tap....NOT something you want to mess with. 60MPH is generally UNSAFE on a MAB, and it also attracts all kinds of unwanted attention from the police, again, AVOID! Most modern huffy bikes are built a lot better today then they used to be, back in the day they used nylon balls instead of metal balls for the bearings! PLASTIC bearings! Good luck!
  20. keatonx

    keatonx Member

    Donovan321 I think you might be confusing me with the OP :jester: