Motorized Rocky Mountain RM7 -Super Motard-

Discussion in 'Photos & Bicycle Builds' started by lowracer, Mar 7, 2010.

  1. lowracer

    lowracer Member

    I finally got my winter project ready to ride...I decided on a Subaru-Robin 4 stroke 35cc & Front belt drive powertrain providing 2 wheel drive (since I am an avid cyclist & enjoy pedaling). The front drive is a rim hoop, JB welded to the front rim & an automotive standard notched 78" V-Belt with a skateboard wheel tensioner & a 1.5" front V-pulley from McMaster Carr. The gear ratio is similar to a friction drive without the need for jackshafts or further reduction.The mount is just some steel bar & 'L' brackets found at the local Lowe's Home Improvement store. I wanted to keep this project cheap & under the price of any kit available such as Gebe/BMP/Staton/Friction & with no welding. I am good at hacksawing & drilling but nothing more hi tech than I got the new Subaru engine/clutch housing from Staton off eBay w/Bing discount for $248 & the rest was under $50. The throttle is a bicycle brake lever mounted to the left side handlebar above the front disc brake lever. The 7" front suspension still works perfectly & well matched to the 7" travel suspension in the rear...

    Attached Files:

    Last edited: Mar 7, 2010

  2. professor

    professor Active Member

    If it works as good as it looks, you will be one happy camper.
    JB welded rim will make the stock rim stronger. Great idea! I love your ingenuity!
  3. Neon

    Neon Member

    That bike looks completely awesome. Are those 700c rims and tires on there? If they are they certainly wouldn't be my first choice. But i live in a very rough pot hole infested road no matter what time of year it is. i need something that is a little less prone to bending themselves all out of shape when i hit a pot hole.
    But that is just me. Once again awesome bike.
  4. lowracer

    lowracer Member

    The rims are the stock 26" MTB (559) wide Sun Rhyno's. The tires are narrow high pressure 1.5 slicks for MTB's. These roll real fast & dont get many flats. The 7" of plush suspension keep the potholes & curbs from giving pinch flats.
  5. Neon

    Neon Member

    Thanks for the info. I've already toasted 2 700c rear rims on my electric bike. And the speeds i get from it don't come anywhere close to the speeds i get with my gas bike. They are both hardtails and the 26 x 2.00 on the gas bike have never once gotten out of true or gone flat. Your rims and tires sound the the ultimate setup to me though.
  6. Neon

    Neon Member

    btw what do you have hanging of the back of your seat post? I have no idea what it is.
  7. lowracer

    lowracer Member

    Agreed, smaller wheels are stronger wheels when all other factors are the same (spoke guage & count, rim thickness & width). I chose this bike to motorize since it is a Downhill/Freeride bike & built extra tough for that purpose @ 42 lbs stock.
  8. lowracer

    lowracer Member

    The thing hanging off the back of the seatpost is a water bottle holder. They are commonplace on Time-trial/Triathlon bicycles but I use it to hold two 22 oz MSR Fuel bottles full of unleaded gasoline for longer distances between gas station visits. I use two velco straps around each fuel bottle to totally secure them to each bottle cage (no jumping out gas tanks):sweatdrop: I just added a few more pics showing the MSR tanks & new larger Kryptos skateboard wheel belt tensioner.
    Last edited: Mar 7, 2010
  9. augidog

    augidog Banned

    lowracer: i can fully appreciate everything about your "Motor-Assisted-Bicycle" and your pedaling-attitude...clearly, you've been "read read read"-ing a lot of stuff at MBc...i think your creation is awesome :cool2:
    Last edited: Mar 7, 2010
  10. lowracer

    lowracer Member

    The people & info on this website are awesome...Discovering has really sparked my interest & imagination to make this project happen. Many thanks to all who contribute here...
    -Lowracer- :idea:
  11. Lower racer firstly great job!

    secondly i look at alot of bolt on engines and just think its...too easy.

    What i ilove about your project is it hasent just been bolted on, YOU have carefully considerd the design to suit YOUR needs.

    why didnt you just go for a front mount GEBE?

    did you consider a 3 speed hub? as you can get some narrow ones e.g.

    (i think the OLD is 110mm, which i think you can fit in most modern suspension forks)

    well done!:grin5:

    p.s im sure you have seen it already heres my baby, i agree it seems that fwd seem common with those whom are already "avid" cyclists and not wanting to effect the pedal drivetrain
  12. lowracer

    lowracer Member


    Thanks...I did consider the Gebe kit & almost bought one. The 2 reasons for my DIY setup:

    1) The Gebe is $600. I spent $300 (w/same new Robin-Subaru engine).

    2) When I was a kid, I built my 1st MotoredBike using this same rim to rim pulley system & V-Belt drive that worked beautifully. (2hp Briggs&Stratton, 20" wheels, Banana seat, No pedals, 700c frame & fork, Stingray pull back handlebars, Engine plate welded into frame, Mens leather belt cinched around frame & engine to keep things from vibrating to much, direct drive (no clutch, no brakes, just engine braking and

    Now 35 years later, I wanted to duplicate it on a much nicer bike. I am a firm believer in the K.I.S.S principal (keeping it simple) & with this design, the only permanent alteration to the bicycle is the extra rim hoop attached to the front wheel. I can remove a few bolts, swap tires & have the DH MTB back in action.

    It seems the major engineering challenge using these smaller engines is getting the correct gearing @ around a 18:1 ratio. The MTB size rim hoop is actually 21.5" across & the 1.5" pulley is actually about 1.2" measured at the bottom of the V-belt. Internally geared hubs, Jackshafts, Gear boxes, Friction drive rollers, & Spoke mounted pulleys all seem like expensive alternatives to simply attaching another rim hoop to get that ratio. Aside from the engine, everything else I needed cost $50 (pulley, belt, steel bar, L brackets, nuts, bolts, JB Weld). I already had the rim, skateboard wheel, brake lever & cable for throttle.

    I may experiment with a rear rack mount just to see how it performs & even a pusher trailer setup both using the same drivetrain (I have an old child trailer sitting in the garage just begging to be cut up & motored...

    Last edited: Mar 8, 2010
  13. moped-dan

    moped-dan Guest

    I like your setup a lot that looks great. How sturdy are the rims glued together? No worries of it coming off?
  14. lowracer

    lowracer Member

    I have put some miles on the bike since I finished the project last month & so far so good. During the build, a few members mentioned that they would secure the rim to rim pulley with more than just JB Weld. I have owned an aluminum AVD Windcheetah Trike that was completely 'glued' together w/ Loctite & never had a problem with many miles of fast, hard riding.
    I have thought about this & as a safety precaution may drill 4 small holes thru both wheels & use steel pop rivets to fasten the wheels. I'll have to file down one side of the inside rivet to prevent interference with the tire bead seat & then cover the rivet with some JB weld & maybe some HD fiberglass reinforced strapping tape (I also use as my rim strips) to keep the tube from flattening due to the rivets. The other side of the rivet near the belt will probably also need some cleaning up to keep it from scratching up the side of the belt (not much clearance here). Pop riveting just 4 points should be enough since the circle is so large.
    Last edited: Mar 14, 2010
  15. lowracer

    lowracer Member

    I added a few more close-up pics of front drivetrain...

    Attached Files:

  16. Hi lowracer,

    still loving that bike :)

    taken it off road yet?

    the suspension is an awful lot to waste on the street. :)

    I just wonder how it perfoms given that i imagine down hill is to fast to need and motor and up hill you must need to switch weight to front wheel to keep traction just thinking (which may not be a good thing the thinking of course.)

  17. lowracer

    lowracer Member

    Fireball jones,

    I haven't taken it offroad as it is set up for road riding w/ high pressure slick 1.5 road tires @ 100 (psi). The plush suspension, straight up moto position, and bombproof DH frame make for a wonderful road machine.

  18. lowracer

    lowracer Member

    I've put a few hundred miles on the engine now & all is well. The JB Welded rim to rim pulley has held up fine. Its getting close to 130 MPG's. It'll do 32-35 mph @ WOT on flat ground in an aero tuck. Not bad for the little Robin E035 on a 55 lb HD bike with a 165 lb rider.
    I've begun a new project & it will be a rear drive, rack mount, w/whizzer sheave & v-belt drive on a Litespeed Obed titanium hardtail MTB w/ front shock & high pressure slicks. I may even add triathlon style aero bars to rest my forearms on while riding. I may go huge & install a 5-6 hp Harbor Freight engine & get a 49cc sticker for it. -Alex-
  19. ibdennyak

    ibdennyak Guest

    Like your bike. Been collecting parts to do about the same thing for a year or two. Glad to hear the JB Weld works. That was something I hadn't considered trying. So far I have a Honda GX25 and xtra rim for it. Love the simplicity of the belt drive. Kind of like friction drive without the wet problems. You have inspired me to finish mine. :grin5::bowdown:
  20. lowracer

    lowracer Member

    The JB weld works great (so far). I also like to use it to join two pieces of metal with a nut/bolt combo for a permanent attachment (I don't weld). I am not too sure about the belt drive & wet slippage. I haven't run it in the wet weather yet, but the rim pulley isn't a normal V-pulley where the belt is using its sides for friction. Here its only grabbing on the bottom of the belt, but since it grabs such a large surface area, it may keep it from slipping? Guess I gotta go riding in the rain to test out this -Alex-