New Build: HF 79cc, Full Suspension, Extra-long MB

MikeJ

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May 5, 2009
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Location
Colorado Springs
Hi Everyone -

Here is my latest build (read: prototype) on which I have been spending a few hours here and there over the past few months. Photos should be attached.

Comfort for long-haul bike rides was a major factor in this build. A previous build using a 2-cycle engine rode well on smooth surfaces, but I took a beating on rough roads. With this frame, I got balloon tires, shocks up front and in back, a better seat, and a less vibrating engine. There is almost no beating sent to the rider. The rear wheel frame pivots freely at the dropouts of the leading frame.

I took frames of three bikes and combined them together. All three were steel frame mountain bikes: A 1994 Mtn Tek Extreme for the main frame and a Specialized Hardrock for the back part. The third bike contributed very little. All other parts are new out of necessity or desire:

Front Rock Shox Dart 2 up front from a local bike dealer,
79 cc 4-cycle engine from Harbor Freight,
Extra-wide bottom bracket and drivetrain pieces from Sick Bike Parts,
34 tooth MegaGear assembly from Sick Bike Parts,
Derailler, chains, and wheels from a local bike dealer,
Gas tank, throttle control and cables from Piston Bikes,
Scooter shock from ScooterParts4Less.com,
Copper exhaust line and lots of hardware from Ace Hardware,
Bearings from local industrial parts outlet,
Engine platform and lots of JB Weld from Home Depot,
Centrifugal belt clutch from MaxTorque,
Multi-horsepower rated drive belt from Auto Zone.

Yellow electrical tape covers a couple of places that I have to touch-up with the yellow paint.

There was no additional hot welding done at all to this build. I can remove the back pivoting frame and rebuild a standard-length bicycle out of everything you see in the pictures.

The bike rides nice without the engine and drive train. Today's test ride was with engine in place but without engine power. With an engine this wide, I will not pedal much; just enough to get it moving before engaging the clutch. That MegaGear will be a necessity when taking on long hills or pedaling without the engine. Going on flat land, gears 3 and 4 will be nice to have. I think it will ride like an underpowered early-60's Cadillac.

The bike's absolute length is 84 inches; won't fit nicely in a pickup truck.
The horizontal bar is 33 inches above the ground at back of gas tank,
Tires are puncture resistant; 26 inches by 2.3 inches.
Both wheels need disc brakes; a rear wheel disc brake assembly is on order.
The engine platform is dense oak: 2.25" x 5" x 18". It is JB Welded to the frame and compressed together also by side-to-side bolts.
Pillowblock bearings for the jackshaft are overkill, but they will not die.

The bike as you see it (dry tank) weighs 87 pounds: 47 up front and 40 in back. (It must be the fast drying paint that is adding all that weight.) Weight creep is like middle age; Every extra part may add strength and functionality, but also an extra pound, or two, or four. . . .

It still needs a kickstand, speedometer, tachometer, some lights that will be seen a half mile away, and a rack extending over the back wheel. There are only a few more parts to be installed. I already have a good, DOT-rated high-visibility motorcycle helmet, a bright yellow jacket and leather gloves.

The pulley ratio is 3:1; the jackshaft to bottom bracket ration is 48:10. This works out to about a 15:1 drive train ratio. This is good; I computed that low-30 mph range will be little work for the engine.

As big and heavy as this build is, I should park it in Compact Car Only spaces.

I have more pictures of the in-progress build, but I figured a few here and more in the future will be welcomed. Let me know what you might have done to make this motorized bike better (like avoid excess weight).

MikeJ
 

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How well does the chain do with the pivot? Nice clean looking build. I like the way the wood work came out.
 
MikeJ,
I really like what you've done here!
Great Build...
Before finding your thread, I was googling the Xtracycle & Surly Big Dummy. I was thinking of something similar using a donor bike attached at its bottom bracket to the main bikes' dropouts, but trying to figure out a way to mount my Lifan 97cc low like on the main bikes' chainstays?
-lowracer-
 
MikeJ,
I really like what you've done here!
Great Build...
Before finding your thread, I was googling the Xtracycle & Surly Big Dummy. I was thinking of something similar using a donor bike attached at its bottom bracket to the main bikes' dropouts, but trying to figure out a way to mount my Lifan 97cc low like on the main bikes' chainstays?
-lowracer-

Ha.....sounds familiar, I went through the same process. I have a collection of parts to do just that. In my case, I make my own suspension triangles from scratch to get the length and height clearance, but using existing bushings etc. I have a couple of the same engines as you laying around, so that seems like a good power source. This is an upgrade of the stretch I have been riding the past year with the low mount engine. My only objection on that one is no rear suspension....but it certainly is stable and smooth.

Will be starting on that as soon as I finish my front wheel drive with the Mitsubishi clone electric start and studded tires for winter using the double rim drive idea that I am stealing from you. :devilish:
 
Nice looking bike Mike. When I read about the wood engine mounts I wondered, but after seeing it.....I like it. :bowdown:
 
Great job and great thinking.
After richening up the main jet a tad on my HF, the choke can be turned off after a couple of minutes (rather than many minutes) it has been a quality engine.

To me, your bike is not heavy. Long for sure though.

I have been thinking of changing the frame in back of mine by welding in a rear traiangle from a suspension bike and re-working the frame, but would like to keep the separate right side drive chain. I like to be able to pedal with the engine up to 20 mph or so. Are you able to do that?
 
I was thinking of using my whizzer sheave & max torque pulley clutch directly on the left side & keep the right side for pedaling.
Since my pusher trailer was a flop (no pun intended) & my rear rack lifan is great up to a certain speed, I'm thinking the added wheelbase would aid handling at speed?
-lowracer-
 
Here is the trade off- long wheelbase= hi speed stability/ low speed sluggishness in turning. Opposite for short wheelbase.
 
MikeJ,
You got my wheels turning.
Did you bolt the rear dropouts from the front section directly to a bottom bracket from the rear section?
Any spacers required or a direct bolt together?
How is the torsional rigidity between sections?
Thanks
-lowracer-
 
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