motorized pit bike chopper build

[4agshoob]

Ive searched the webz for a total of about 10 combined hours looking for something that would work that wouldnt cost over $50.

I did find 1 NOS kind 200 that was 7" with a 750lbs spring for $20, but only 1... i need 2 matching.

So, as a last resort i researched the bike the shock i currently have, came off of. The Genesis v-2100. Made by Kent international. Gave em a ring, told em i need 2 replacement shocks. $37 shipped for both!

So those are on the way!!!

 

[4agshoob]

Made a helluva discovery tonight tinkering around. Decided to mess around with some pitch angle on how the spring gets compressed, because:

The way its set up right now, the axle moves about 2", and only squishes the spring about 1/4" as the spring rotates forward. Then right before bottom out of the frame to the ground, the pivot rolls harder and tries compressing the spring significantly.

So, i played with one angle, and it was success!!! 1 spring held my weight, just like the first time.... then the frame slowly settle to the ground...

WHISKEY TANGO FOXROT!!!

AGAIN, i marinate on a smoke while studying the frame, then i seen it.... the rear forks are bending!! With the lower loop hooked to the pivot, and the upper loop supporting my weight on the shock, its spreading the "V" apart.

Time to see if i can get it slightly bent back, and weld in a bar connecting the 2 loops top to bottom in the spring/swing arm area.

Lets see if i can do this without p*ssing my neighbors off now at 8pm, lol.

 

[Fv2]

Don't forget pics.

 

[4agshoob]

Don't forget pics.

Too late..

Everyone would have gotten a kick at how i bent them back. Put a jack at the base of the bottom of the bottom tube where the pivot hinge is, stuck the top side under the bottom rail of a hand rail, and proceeded to jack. Tried using my truck trailer hitch, but even aired all the way up, it was still too low (bagged 93 s10 ext cab, hehe)

Took the spread from 9 3/4" back to 7 3/8". A little under 2-1/2" is how much the "V" had bent. Its a little too late to cut steel tonight to make the "spine". More on that tomorrow.

But heres you a pic.....lol

 

[4agshoob]

moving on with my design as I wait on parts. UPS says my engine kit should be here Friday. I definitely know ill be using a jack shaft to transfer power from the left side, to the right side.

I found this:

http://motorbicycling.com/showthread.php?t=12284

pretty much my thoughts, except; the distance between my jack shaft and my engine will be about 12". my jack shaft will mount right in front of the seat post, dang near on the bottom frame rail. I really like that guys engine mount technique. may have to adopt that, errrr something close.

oh, I did hear back from Jim over at Peddlechoppers.com on that sturmy archer 3 speed occ rear wheel with disc brake, $329 shipped. that wheel is the exact reason im using a jack shaft.

does anyone know if sturmy archer hubs have interchangeable sprocket sizes? eg: say it has a 14t sprocket, do they make like an 18t sturmy archer sprocket?

 

[4agshoob]

I did find sturmy archer sprockets ranging from 13t to 20t, $10 a piece. That makes me feel a bit better, that ill be able to play with the gearing.

Photodump:

Exactly how my jackshaft setup will be:

Mounted from the center....

But with about this length of chain from the engine to the shaft:

 

[4agshoob]

Don't forget pics.

As i got to looking in my pics compilation, you can actually see the rear "control arm" bending starting at my first pic. Watch how the angle of the shock changes too from the 1st picture and the last picture, even though i added an even more linear mount on the upper swing arm:

Original:

After 1st test:

The angle that held my weight before the frame sunk to the floor slowly:

I could tell by my shock angle continually getting more verticle, no matter what i did, that something wasnt right.


The i noticed paint flacking off right in front of the rear drop outs, a closer look, and that part of the frame was responsible for 250lbs spreading it apart.


A. It "twisted" this area. The part of the hoop that would have originally mated against the chain stay, is still strait on the pivot i welded in, but as the tubes round the radius to head out to the drop outs, theyre rotated in a down ward fasion.

B. Right in front of the drop outs, i found the weak spot. This is where most of the bending occured.

From my steel erection experience (giggity), i know a triangle is the stongest shape possible when it comes to structural support and weight bearing. However an open end up triangle or "v" doesnt have any support to close the triangle, this was my issue.

 

[Fv2]

I wondered how well the rear triangle would hold up without a solid connection to the frame, I'm learning alot about using an occ bike as a swingarm.

 

[4agshoob]

I wondered how well the rear triangle would hold up without a solid connection to the frame, I'm learning alot about using an occ bike as a swingarm.

These bikes (OCC) are incredibly "soft". The frame walls are less than 1mm thick. Im guessing somewhere around 14-16ga. steel. Im sure it was intentional for weight sake.

Put it this way: that teal upper bar scab was from a Next girls 18" bicycle, and its steel is like schedule 40, way thicker than the sting ray frame.

 

[4agshoob]

Well isnt this the cutest little thing youve ever seen.......

Uhhh......

Well then, moving on.

212cc slant 6.5hp 4 stroke it is! Maybe.... this thing is incredibly tiny compared the the bike....

This 80cc may very well find its way onto my sons 20" pedal bobber. Looks like ill be modifying his frame's top tube, sooner than i thought.

Aft thought: i have enough room to run 2 of these 80cc's in linear sequence..... but thats another $100 and 160cc ... while the predator is $130 and 212cc. I suppose i could off set them, run dual gears on the engine side of the jack shaft, run a gyro splitter on the throttle cable to each carb, as well as the clutches Twin engine, 2 cylinders, 2 stroke. May be worth looking into for frankenstein' sake.

I just dont forsee this little engine pulling my fatarse up any kind of incline, no matter how slight the grade or gear reduction niggonometry i pull off.....

 

[Nocash18]

Too late..

Everyone would have gotten a kick at how i bent them back. Put a jack at the base of the bottom of the bottom tube where the pivot hinge is, stuck the top side under the bottom rail of a hand rail, and proceeded to jack. Tried using my truck trailer hitch, but even aired all the way up, it was still too low (bagged 93 s10 ext cab, hehe)

Took the spread from 9 3/4" back to 7 3/8". A little under 2-1/2" is how much the "V" had bent. Its a little too late to cut steel tonight to make the "spine". More on that tomorrow.

But heres you a pic.....lol

I used to have an s10 with about the same stance. It was a 91 with a 2.8 5speed. I had the frame rails about 2, maybe 2.5 inches off the ground. Never did get around to doing a body drop though.

 

[4agshoob]

I used to have an s10 with about the same stance. It was a 91 with a 2.8 5speed. I had the frame rails about 2, maybe 2.5 inches off the ground. Never did get around to doing a body drop though.

Mine was an original 2.8l 5 speed. Now its a 3.4l, 2.8 heads and intake with a 4.3 tbi. 3:73 out back, still 5 speed. 93' tahoe package. Everything but power windows (thank god). I love my truck, and work out of my truck daily. I get asked all the time "why work out of a lowered truck?" Because i move appliances daily by myself, you know how nice it is to dolly a side by side fridge onto a tailgate that is 8" off the ground? Lovely, thats what it is, lol. Fully aired up, my front subframe is about 2" off the ground. Its sitting on a 6/7 drop before the bags. Lays frame hard, and still low when its "up", lol.

 

[4agshoob]

Didnt get a chance to get into the garage tonight....honestly im kinda discouraged by how tiny the engine looks in the frame. But im gonna give it a whirl... especially after some of the videos ive watched on 44t and 48t fixed sprokets look pretty.... "ok".

Frankensteining 2 engines together is still in my mind somewhere back in there, whether it be side by side and locking the final drives together (single clutch on drive end) or linear, one in front of the other, offset with 2 drive cogs on the input side of the jack shaft.

Oh well.... i wont go there, unless i feel i need to.

Moving on.... i did find that Jim uses 18t (assuming he uses what comes in the kit) on the sturmy archer 3 speed hubs. So i did some equations to achieve the best range possible.

Motor: 10t
Jack in: 20t
Jack out: 9t
Sprocket:18t

Sturmy archers are 120% ratio's low and high. 2nd or center gear is drive/drive.

Drive ratio's will be as followed:

Low: 4.30:1
2nd: 4.00:1
3rd: 3.70:1

Those arent bad numbers, (in reference to my knowledge in automobiles). Especially driving a 20" wheel, and not a 24-26".

However, if i wanted an even lower gear for take off, i could always change the SA hub out for a 20t.

Motor: 10t
Jack in: 20t
Jack out: 9t
Sprocket: 20t

Low: 4.80:1
2nd: 4.30:1
3rd 4.00:1

With this setup, my top speed would be determined on rpms. Most people with engine to wheel at 10t motor/ 40t wheel on a 24" is around 38mph. Plenty fast for me. Plus with this ratio, its like having the benefit of a 48t, 44t, and 40t wheel sprocket, all at once.

For reference, 10t motor w/ 44t wheel is a 4.40:1 as a 10t motor w/48t wheel is a 4.80:1.

Jim claims you can start from a dead stop with the clutch/throttle like a standard motorcycle, with the SA in low. It looks like in his pics his jack in is a 20t, and maybe 15t on the jack out, dont quote that, thats just studying pics. If thats the case, then my setup on the jackshaft is going to provide ample torque through gear reduction.

 

[horsefarmer]

How do you shift SA hub when engine running and bike moving? I stop pedaling when shifting mine.

 

[4agshoob]

How do you shift SA hub when engine running and bike moving? I stop pedaling when shifting mine.

Thats a good question. How old is your SA hub? Maybe the new ones allow shifting while in motion. Ill have to youtube/investigate that.

Last night and some of this morning, i started investigating 212cc predator motors. Honestly, its a cheaper, more powerful route in all directions. Its asthetically pleasing too, as far as size, the CVT converter, exhaust sound, etc. Has more of a "chopper" feel than this 80cc super gear reduced. Thats another thing as well, i wouldnt have to worry about a 3 speed hub to be custom built, if i can shift while moving, etc, because the changing ratio converter will be multi range.

Id still use a jack shaft, and id have to figure out how to mount a disc brake to the rear wheel. As far as mounting the 212, to lessen that "impact" feeling from a 4 stroke, id mount the motor on a rubber mat on a steel plate, and use washers/old valve springs with nylon lock nuts to create a damper style mounting.

I think i may pull the trigger on the 212, and mount this 80 on my sons bike so he can putt around with pops.

 

[4agshoob]

Right around 2:10, thats whats up!!

 

[4agshoob]

At hits 47mph in this video.... more than i care to go, lol.

 

[4agshoob]

Going to check this tank out this weekend:

http://atlanta.craigslist.org/nat/mpo/5985146273.html

 

[4agshoob]

Managed to get about 30 minutes in the garage tonight. Got the rear swing arm braces in. Thats all for now.

 

[4agshoob]

So, i guess the linear twin engines has been done.

Pretty effin cool!!

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