Building a 2004 Yeti DH-9 with 40cc Tanaka

hawaiioutdoors

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Jun 18, 2008
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Aloha from The Big Island of Hawaii, with snow on MaunaKea 13000 foot elevation, and Lava on the slopes of MaunaLoa...plus the sun and surf.
OK, after researching for over a year, looking at the Bionics, Matt Shumaker's recombant, being inspired by project M85, and the concept Derbi 2.0... I would put links to all these cool bikes, but this website wont let me.
I'm building my first motor-bike. A 2004 yeti DH-9, with a GEBE Tanaka 40cc. I'm building a custom rear wheel using a 1.6 x 21 excel rim from a dirt-bike, stainless 10 guage 36 spokes laced to a Chris King heavy duty hub, the rear tire will be a Michelin 2.75 x 21 trials tire. hopefully this will be an almost indistructable combination.
I enjoy pedaling, but sometimes the terrain gets pretty steep.
Any and all advice will be appreciated, both positive and the not so positive.
 

MB-Monkey

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Nov 19, 2008
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Manchester TN USA
Mahalo guy,

glad you joined us. Spent time in the islands as a kid and miss it a lot. hope you find what your looking for. post 5 or 6 messages and you will be able to post links and pics. good luck.
 

hawaiioutdoors

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Jun 18, 2008
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Pictures are coming.... I put the GEBE Tanaka 40cc on the Yeti. DH-9.
I adjusted (BEND) the mounting strap to the wider width of the rear bolt thru axle. The rear tire is a 2.7...wide for a bicycle.
I drilled the strap to so it can be bolted to the top swingarm link.
The motor moves up and down with the swing-arm.The tenioner keeps the belt tight.
I first tried the motor as close to center of the bike as I could.
It positioned just to the rear of the seat. The problem with this was that my butt kept hitting the sprark plug, and the exhaust heated up the rear of my right leg.
I had used a sail-boat turnbuckle for the rear strap so the engine (forward/rearward) position is easily adjusted.
I cranked out the the turnbuckle making the engine sit way back....only thing with this is that the gastank filler is now the lowest part.
On the 1st maiden voyage, On my way to work, the drive belt sprocket flew off some-where, and the belt got shreded. Not a good start. I would think that GEBE would have made the sprocket have a reverse thread so that it tightens while it is running...not so. Bye..Bye belt sprocket, bye bye belt.
I also sent out an excel 21x1.6 motor cycle rim with a swiss made rear bicycle hub to be laced by (The Wheelmaster) with 9 or 10 gauge spokes as he sees fit.
The adventure continues.....trk
 

AndyT

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Mar 27, 2009
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Franklin, TN
I spoke to GEBE today and asked a few questions. They said it was important to maintain the 14.5 " (I thnk) dimension from the axle to the top of the mounting strap. If you bent and drilled, you most likely changed that dimension, unless you measured and were careful. This may cause a tension problem on the belt.

Also does that motorcycle rim have the same number of spoke as the drive ring you bought with your kit? If not it won't snap in place.

A call to GEBE should get you straightened out. They seem very cool.
 

hawaiioutdoors

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Jun 18, 2008
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UPDATE: What I wanted to build was a light weight yet solid motorized bicycle. So I started with a frame that I really liked (2004 Yeti DH-9) and tried to adapt parts to fit that frame. The bicycle was to be used for recreation (weekend trail rides) as well as commuting to work aprox 5 miles away. I wanted it light enough so that it could be easily lifted, carried, and "flicking" it when on on the fly ( getting it to move around obsticals when flying down a hill).
What I ended up with is a heavy (aprox 90 lbs) cumbersom unwelding, under powered thingy...not nearly as nimble as a bicycle, and way less power then a motorcycle.
Couple of things I learned.
1) weight is not your friend.
Keep all the parts as light and as strong as possible... The GEBE Tanaka 40cc weight is aprox 17 lbs without gas. This sat on the rear swingarm above the rear tire.
The custom rear rim and tire was aprox 10 lbs... The spokes were 9 gauge. overbuilt... The tire and inner tube were for a motocross dirt bike so was built for abuse, but was way too heavy...

2)GEBE knows their nich market...and have built a wonderfull kit...good for urban commuting...but, dont mess with it.
The engine has to sit about 14.5 inches above the rear axle, so that the belt will fit.
The rear tire should not be wider then 2.1 wide so that the tire does not rub the custom belt...
 
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AndyT

New Member
Mar 27, 2009
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Franklin, TN
hawaiioutdoors,

I have the GEBE Tanaka 33 kit and I couldn't be happier. I started with a $440. (less 20% on sale) REI Metro "comfort" mountain bike with front shocks. It weighed 31 lbs stock. I installed the kit per instructions, added lights, a coil type lock, a tool kit with everything I need for a quick repair/flat fix, including an extra belt (not needed so far), and it weighs about 50lbs. The Tanaka 33 engine weighs about 3 pounds less though. I kept the stock 36 spoke wheel (wheels were fairly decent quality) and wire tied the spokes for added strength and it's doing great. With the stock gearing, it will do 30mph, and climb the hills around here without slowing too much, but you still need to pedal up to about 12mph to give the clutch a break. With trail gearing, I'm sure it would pull better, but I'd lose top speed.

As you say, it's best not to mess with the kit. If you mod the mounting and keep the 14.5 inch dimension correct, there should be no problem though. And you are right about these 33cc and 40cc kits being better for commuting and possibly easy trail rides. They won't turn your bike into a motorcycle.