Author Topic: HolmenTree Bikesaw Resurrection  (Read 6105 times)

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Offline HolmenTree

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Re: HolmenTree Bikesaw Resurrection
« on: December 30, 2016, 12:39:34 am »
Now you're probably wondering why I didn't build a 250 moto cross engine saw.
Well way back in 1983 my intention was to compete exclusively in the Canadian PNW.  Canlog rules out there maintained 140cc maximum displacement for hot saw.
So I went 125 ...with over 30 horsepower factory they were competition for the Kart saws.

So here I am wanting to redesign my Yamaha 125 with massive weight reduction and compactness. Already the powerhead only weighs 32 lbs with lots of room to get it into the 20's.
So with my plans to go right hand drive I had several decisions....rotate cylinder and piston and ignition then run engine backwards, or....rotate crank and ignition, or....Lay engine on back with carb up to right hand drive and run engine rotation backwards with ignition reversed 180 degree .

Well I concluded after pulling the rewind housing and the starter cup off the rotor. Why not run the drive sprocket off the rotor.
From looking at the Jack Stewart/Sven Johnson 250 CanAm Rotax bike saw rebuild that Ken Steeves did...the drive sprocket was driving off a single long shaft held to the crank with 8 small screws.
 This shaft held the ignition, clutch, rim sprocket  and rewind starter. And that powerfull saw won Hayward, Wisconsin 7 years in a row. 8) Best time 8.03 seconds in 3 cuts of 20" pine with cold start.

So as my pics show with the starter cup removed what I'll  do is re-thread the rotor puller threads in the rotor to left hand thread.
Build a 2 piece shaft with both pieces left hand thread. The piece threaded into the rotor will be locked with a internal nut on the crank. Supported by a sealed bearing and seal in a aluminum side cover sealing the ignition. The 2nd piece external shaft will left hand thread into the base shaft with a standard 7 spline welded to it, holding the 11-13 tooth Danzco rim sprocket. With a washer and C clip on the end. Different size rims can be easily swapped for different wood.
B/C will still be very close to crankcase centerline.

A new aluminium rewind rope spool will be mounted on the left side crank end replacing the old 11 tooth spur sprocket.
Left hand rewind rope position will be a natural fit for a quick cold start as the saw is lifted and started at the same time.



Making a living with a saw since age 16.
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