chainsaw motor ideas

[crazygringo]

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

 

[crazygringo]

continued from above

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

 

[NunyaBidness]

aw cmon
no one has any ideas? comments?

 

[srdavo]

since you asked......

(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.

 

[NunyaBidness]

move away
we are wanting to use this http://webcyclery.com/product.php?productid=16644&cat=0&page=1 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

 

[srdavo]

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.

 

[NunyaBidness]

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

 

[srdavo]

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?)

 

[crazygringo]

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

 

[crazeehorse]

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