Found a Cool Engine. What Now?

Discussion in 'General Questions' started by flashstar, Apr 13, 2014.

  1. flashstar

    flashstar Member

    After building HS 50cc, a HT 70 and a GT50R CAG bikes, I decided that I am ready for something a bit more reliable, powerful, and comfortable (but still a motorized bike). These engines have many upsides and drawbacks but none provide quality electrical power generation, reliable starters, or transmissions.

    For me, these requirements mean finding an engine that includes true power generation abilities and is shift-able for comfortable mid-thirties cruising. I thought that a high performance 4-stroke would give me what I was looking for.

    I spent a long time perusing Ebay and Alibaba for an engine without too much success. I almost settled on the CG125 engine, however I could only find a couple in the states due to overburdensome EPA regulations. I was also concerned that 125cc and around 11 hp would be too much for a bike frame. The smaller Honda clones are typically horizontal engines and may have trouble fitting almost any frame.

    I called up and they gave me a ton of very helpful engine suggestions. We decided that I should consider engines from small Enduro dirt bikes. After quite a bit of searching, I realized that the XR80 might be the perfect engine for my goals. With 110 watts of power generating capabilities, it can drive a fuel injection setup, a headlight and a tail light! This engine also has 5 close-ratio gears, a light crankshaft, kick-start, and a 9.7:1 compression ratio. Topping off the engine package is the fact that it produces ~5hp and weighs no more than ~45lbs. Finally, I have heard that the XR80 is incredibly reliable.

    At 10.5" wide, the XR80 engine is narrower than my HS50 with Grubee 4G.

    $315 netted me a clean real Honda XR80 engine with 180 psi compression! It should include a pre-wound stator to help charge a motorcycle headlight since I got it off an Enduro bike. The seller also gave me his Big Gun exhaust for only $80. Finally, I picked up a service manual, wiring harness, and carb.

    Here's the rub though. I could not find information on the height of this engine online. It turns out that the motor is between 14" and 15" tall, probably due to the OHC design.

    What should I do? Should I try to find/ modify a frame to fit this engine or should I try to source another type of engine? I do not mind adding a drop loop to a frame if it isn't too much money.

    I feel like the Felt Bixby Cruiser is a close fit, however I do not have any specs on the space inside the frame. The benefit of the XR80 is that the jug does not look enormous (only 10cc larger than a HT 70).

    Note that the engine mounts are in the front and rear of the engine. I should not have to support the engine from the bottom.

    Thanks very much! Pictures are attached.

    2014-04-12 23.51.16small.jpg 2014-04-12 23.51.37small.jpg 2014-04-12 23.51.43small.jpg

  2. IbedaYank

    IbedaYank Member

    Mod a cycle frame to make a set of pedals work or build a frame that has the correct style of motormounts for this engine and use at least moped hubs as you will tear up bicycle hubs in short order.
    17inch motorcycle wheels can be found pretty cheap as they normally came on sub 125cc cycles.
  3. Fabian

    Fabian Well-Known Member

    That's an awfully heavy engine.
  4. darwin

    darwin Well-Known Member

    OP get a large frame bike, say a 21/22". Motor would have to fit the V then.
  5. flashstar

    flashstar Member

    Engine Comparison Pictures

    Hey guys, thanks for the information. I think that I will try to find/modify/build a frame to fit this engine. I'm definitely investing in quality wheels and brakes as well. The wheels will have 11/12 gauge spokes. I will keep everyone informed on this build.

    Maybe this engine will become a nice option for motorbikers who would like a bit more power and comfort?

    Here are some better comparison pictures that should give a better idea of the size of this engine. It isn't much larger than a HS50 with 4G transmission in any way except for height. I bet that the HS50 with mount and transmission is greater than 30 lbs as well. Note that the red bike with the HS50 uses a 19" frame.

    P.S. The oil left in the engine is light colored so I'm hopeful that it was well cared for.

    dipstickoilsmall.jpg FR engine viewsmall.jpg topdownenginesmall.jpg rearenginesmall.jpg sideenginesmall.jpg
  6. professor

    professor Active Member

    How will you shift it?
    The difficulty with a wide motor is finding room for the pedals.

    When you began this post I thought you might have in mind a snowblower engine that has a stator for lighting power.
  7. flashstar

    flashstar Member

    I am actually looking at a folding, extended shift lever. Then, I'm considering a "pedal lock" to keep the pedals in one place in case I would like to rest my feet while shifting.

    The XR80 engine is actually half an inch narrower than the HS50 with 4G trans. Since I will be mounting this engine lower (and farther forward) in the frame, pedaling might be less awkward than with the HS50.

    If I run into clearance issues with the front sprocket, I could always swap to a smaller one (maybe a 32 tooth?). I pedal occasionally but never very quickly! Then, I will be sure to run an extended pedal crank. Pedals saved my girlfriend's butt when her CAG engine's clutch broke. I was able to pedal with her for 6 miles on the red HS50 bike in the background without trouble.

    Thanks for the great point though professor! I am not completely sure this setup will work out, however I will keep pedals at all costs.
  8. fasteddy

    fasteddy Member


    Not sure how big your budget is but you may want to consider this frame. Pat at Sportsman Flyer has joined up with Worksman Cycles to supply a ready made looped frame bicycle. They may sell just the frame if that's all you want but you would have to call Worksman to see.

    Google Worksman Cycle then go to their recreational site on the header then down to Sportsman Flyer. It comes with or without a gas tank and oil tank/ tool box.

    Google Sportsman Flyer and then look at what he offers for accessories. You will be surprised at what he sells and everything is American made and top quality. Pat and his brother have built and raced record holding Bonneville Salt Flats bikes.
    These are the frames they used.

    Hope this helps.

  9. flashstar

    flashstar Member

    Hi Steve,

    Thanks for the help but I got my engine shipped out to Silver State Cycles. I'm working with Scott on a Board Track Racer-styled bike. It turns out that the XR80 will fit in his frame with over an inch of clearance on the top. He's building custom solid mounts and a floating jack-shaft assembly for around $180. Then, I will only need to adjust chain tension at the rear and an idler will not be necessary.

    I had actually planned to go with a Worksman before finding Silver State Cycles, however I couldn't beat Scott's price. The proof is in the pudding though so I will see what things look like when I get the engine and frame back.

    I also purchased an Ecotrons small engine EFI kit! I'm excited about easier starts and no need to mess with jets. Later, I might upgrade to their EFI kit with traction control for more safety on the road.

    By the way, do you have any recommendations on a headlight and tail light? My stator produces around 100 watts of power and the EFI kit will use around 36 watts. I would like to use a Motorcycle-brightness LED headlight bulb.
  10. dchevygod

    dchevygod Member

    Won't you still need a small battery to power the efi while starting till the stator spins up?

    I'd look into making a handle shifter for it since its illegal to have a manual shifting MB in all 50 states. If a motorcycle cop sees your foot hit a shifter lever and hears the rpm change you may be in for a bad day, not to mention your 31cc's too big on motor size.

    I think its gonna be hard to keep it under 20mph with all that power a hand! Good luck with your build, and watch out for the fuzz!
  11. dchevygod

    dchevygod Member

    6 or 12 volt at 100a? LED's don't use much power and are super bright. I'd suggest finding housings you like and build an led cluster for them at the correct draw so there's enough left for ignition and your EFI.
  12. butre

    butre Well-Known Member

    that is downright false
  13. dchevygod

    dchevygod Member

    All the laws I've read, I'll say that with confidence because a district court judge told me that as I was fighting a ticket for driving on a suspended. And I know that is true for AZ, CA, CO, TX and OR
  14. flashstar

    flashstar Member

    The most feasible idea for a handle shifter is an electrically controlled unit. Pingel's electronic shifters run around $600 though. Scott's fabbing up a swing-out peg so that I could pedal in between shifts. In my opinion, some type of shifter is really essential for a reliable, comfortable commuter. A SBP Shifter might put you in the same area legally as an internal transmission. The worst case scenario is that I will have to register the bike as a motorized cycle. I am equipping it with everything needed to be registered (and more) in case.

    If I need to get her registered, I will consider throwing on the XR100 engine. Then, I could always hop it up to 120cc and get 12hp+.

    After doing more research, I've discovered that the XR80 will hit around 12,000 rpm in slightly modified form. 10,000 rpm with stock cdi, etc. A guy on the thumper talk forum posted a dyno graph showing an XR100 engine hitting 14,000 rpm producing over 12hp! I knew that there was a benefit to this ohc engine. ;)

    My main goal here to to build something that is as reliable and nearly as comfortable as my car. All while keeping the looks somewhat period-correct lol. Think fun board-track style scooter replacement.

    Anyway, I don't believe that Texas limits motor bicycles to 20mph. They just need to be kept to roads where the speed limit is 35mph or less. I feel that the 20mph limit is quite dumb considering that most pedal bikes can exceed that.

    I looked at headlight options and ordered a 5.5" motorcycle headlight. I am going to install a PlasmaGlow igniter LED. Total light output should be over 1500 lumens. I am also installing a 1934 Ford tail light triggered by brake switch with license plate lighting just in case.

    See this wiring diagram I whipped up as well:

    Wiring Diagram.jpg

    I am installing a real keyed ignition switch and a PC-8 fuse box. When the switch is turned on, the EFI kit will receive power. This could double as a good theft deterrent.

    Finally, I received my Ricky Stator rectifier/ DC regulator in the mail today along with my 3700mah nimh battery!

    rectifier and battery.jpg
  15. dchevygod

    dchevygod Member

    If your prepared to register as a moped then I'd do it. It shouldn't be this way but cops like to mess with us every chance they get. I like the build though good job thinking outside the box.

    I never keep to the 20 mph limit I always pedal fast when I see a cop though. At 20 my motor is just barely above the 2500 rpm idle!