chainsaw motor ideas

Discussion in 'Frame Mounted Engines' started by crazygringo, Jul 12, 2008.

  1. crazygringo

    crazygringo Member

    hey folks,
    this is NunyaBidness posting with Gringo here too.
    here's what we're trying to do. We've got a 45cc 4-stroke motor from a Homelite chainsaw. We want to mount this motor in the frame, drive the front chain-ring with the motor. We've got a line on a front free wheel system crank set.
    just looking for ideas/info on mounting and anything else that you folks want to comment on.
    here's some pics of what we've got so far

    Attached Files:

  2. crazygringo

    crazygringo Member

    continued from above

    this is the bike that we want to do this to. poor lil ole thing

    Attached Files:

  3. NunyaBidness

    NunyaBidness Member

    aw cmon
    no one has any ideas? comments?
  4. srdavo

    srdavo Active Member

    since you asked......:lol:

    (I have a similar project brewing in the garage, with a smaller chainsaw engine.)

    the studs that hold the bar in place is an excellent mounting point. you'll prolly need at least one more place to mount, to prevent twisting, under torque.
    I would suggest a bolt-on mounting system, to the frame. (U-bolts) this will allow adjustments for chain alignment, tension, etc.
    Do you plan to use the centrifugal clutch?

    how about gear reductions?

    before we take this too far...I want to move this thread to Frame-Mounted Drive-Trains.
  5. NunyaBidness

    NunyaBidness Member

    move away :)
    we are wanting to use this the drive is on the right hand side, so with that FFS we can use the cog set in the back to shift gears. doing it like that we should be able to use a fairly standard gear reduction, kinda like whats on a 70cc 2 stroke.
    at least that's how we've been thinking
  6. srdavo

    srdavo Active Member

    the chinese bicycle engines have a built-in gear reduction, between the crankshaft gear & the clutch gear....roughly 4:1 , coming off the sprocket. this would be equal to coming off your chainsaw with say, a 10 tooth, to a 40 toothed chainring.
    IMO, we need to be at least 16:1 , so we have enough lowend to pull from a stop, or at least a rolling/pedal start.
  7. NunyaBidness

    NunyaBidness Member

    I was thinking that the rear cassette would give the low end and top end with this setup
    I have been known to think wrong tho lol
  8. srdavo

    srdavo Active Member

    it's still a worthy project.

    mine has been on the back burner for a while...
    I plan to do way with the pedals for mine, for an off-roader.

    rightside..10 tooth to 40 tooth on chainwheel
    the bottom bracket becomes a jackshaft.
    leftside...10 tooth to 48 tooth on the rear wheel

    gets me 19.2:1 reduction...
    at 8000 rpm, I would hit 28 mph. (& possibly kick up some gravel?)
  9. crazygringo

    crazygringo Member

    the bike were using has no front deraileur. I was planning to use the little chain ring for the motor and the big ring in the front to drive the cassette in the rear. Then I could shift to lower gears to start. Thats the way I see it in my mind anyway. After thinking about it for a bit though if I were to use the bigger ring on the motor and the smaller ring for driving the cassette. It would probably be easier to start off. It's a 7 speed cassette though and that should help with the gear ratio.

    theres about 30 teeth on the small ring and about 48 on the large ring I say about because I only counted halfway around then multiplied by 2
    the largest ring on the rear cassette is 28 teeth

    would it ruin the chainsaw or the bike or would it just stop the motor if the gearing was to high

    Here is something else I'm thinking about

    The brake in the chainsaw should it stay or go
    if it stays I have to cut it down so it'll fit in the bike
    If it goes would there be any problems
    Last edited: Jul 13, 2008
  10. crazeehorse

    crazeehorse Member

    is that a 4 stroke?more pics please, i've never seen a 4 stroke chainsaw. i just wanted a closer look.
  11. srdavo

    srdavo Active Member

    I think the brake can go.

    if your are geared too high, it wont pull itself & you'll smoke your clutch.
  12. NunyaBidness

    NunyaBidness Member

  13. crazygringo

    crazygringo Member

    it is a 2-stroke:(
  14. Jax Rhapsody

    Jax Rhapsody Member

    Well if your using the bikes stock rear derailuer, just start in a fairly high(large sproket not numerically) gear and shift when you think the engine is "redlining". Thats how I'm gonna do my trike use the 3speed coaster brake as the transmission. Wanna rig up rear indepedant braking too. but enough of my foolishness...