Sixthreezero Cruiser With Huge Mid-Frame Space!

5-7HEAVEN

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Jun 22, 2007
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Well, I spent my stimulus check! I just received my new Sixthreezero 21-speed cruiser bike through Amazon yesterday. Shipping was quick and cheap($15.00) It has cantilever brakes front and rear. With the exception of disc brakes and suspension fork, it has everything I searched for. It has a 14t-28t 7-speed Shimano cassette and derailleur, which should work fine to channel the engines' power.
The midframe is FIVE INCHES! wider from head tube to seat tube than the new Diamondback cruiser frame I was going to use. I'm trying to mount two pocket bike engines at an angle so they look like a "V-twin" engine. This bike is 4 inches wider at the Diamondback's mounting plate position, so I should be able to able to fit the "V-Twin" or tandem-mounted Tanaka 47R engines. Fully functional pedaling too.

It took years of searching to find a bike like this. My single-engine Diamondback mountain bike has me tiptoeing at a standstill. This bike is almost 5" lower to the ground, so I can stand flatfooted at a stop.


It's important for short-legged senior citizens like me to have solid footing.
 
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Wrench

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ALOHA Braddah. We see da bike Now lets see da v twin set up. Gonna be ono.
 

5-7HEAVEN

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Thanks, Bonefish! Howziit Wrench! Just got the stock bike assembled yesterday. Took measurements and was pleasantly surprised with the larger dimensions. The old motor mounts and plate don't fit because of the Sixthreezero's extra width. Now that there's more room, I'm tempted to go with the super dependable Tanaka engines in tandem position. PB engines in a "V-Twin" formation look super cool, but you know how undependable they can be.

BTW, I'm running both engines' power thru the 7-speed cassette. It's gonna be fun!

Maybe I'll hemo(remove) the Tanaka plastics and try make the "V-Twin" look.

This is one way to pass time during the COVID-19 quarantine.:)
 
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5-7HEAVEN

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I set up a temp motor mount plate to trial-fit pocket bike and Tanaka engines. The Tanaka engines fit in a "V-Twin" arrangement! Now I need to fab an adjustable 60-90* iron "triangle " for both engines to bolt onto. Right now, the rear engine hits the top tube. The engine plate needs to be lowered about 1.5". But first, I need to install the widest bottom bracket I can find. Wider bottom bracket allows the engine to slide further into the midframe and increase clearance for my inner left thigh.
Looks like my Tanaka tuned pipe won't fit, like it did on my mountain bike:(
 

5-7HEAVEN

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Well, I did install a 206mm bottom bracket, the largest I could find.

Both pedals and arms clear the engines by at least half an inch.
It took me a LOT of time to figure out how the V-twin motor mounts on my bike will work out.
When they redesigned and extended this bike's midframe, the manufacturer left a 7-inch stub of the bottom of the original seat tube remaining on my frame . I sawed off 1" of the stub and lowered my motor mounting plate. Then I'll run a 4" bolt to tie the stub with the angle iron brackets supporting the mounting plate.
So the 12" x 5" aluminum plate bolt atop two angle iron brackets which sandwich the seat tube and down tube. A 9" x 5" plate bolts onto the 12" plate. A 5" x 5"x 5" x 1/2" angle aluminum bracket welds atop the 9 x 5 plate, about 1" from the front of the plate's edge.
Sorta like a pup tent with flaps open towards each side of my bike.
The 1/2" sides are drilled and tapped to bolt another section of the motor mounts.

Years ago, I bought a universal motor mount for my engine. The top part sandwiches between the engine and the 5:1 pocket bike gearbox. The bottom section bolts perpendicularly onto a horizontal surtface mount.
Now this bottom part will bolt onto the side of the aluminum triangular "pup tent", forming a 90-degree angle between the bottom of each engine.

Like a big "V".

I should've bought two of these mounts, 'cause they haven't been available since!
So, I've found someone to duplicate this "looking glass mirror-type" engine mount, weld together the aluminum triangle and enlarge the driven sprockets' freewheels' five mounting holes from M6 to M8.
Still waiting for parts to arrive.

Then it's time to engineer the twin drivelines.
 
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5-7HEAVEN

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Each engine will have a 5:1 reduction gearbox on its nose. The front engine is ported/modified, and will have an 11-tooth gearbox sprocket.

Its gear ratios in lowest/highest gear will be 38.18:1 and 19.09:1, respectively. The engine closest to me is stock & will have a 14-tooth on its tranny.
Its low/high gears will be 30:1 and 15:1.

Each engine has its own 72-tooth sprocket. The outboard sprocket mates to a 5-hole freewheel, which screws onto the right-side pedal arm. This connects to the engine closest to me. The inside 72t is siamesed to the outer one. They connect with each other near the freewheel AND with six M8 bolts in a 5.25" bolt circle diameter(BCD).
Five 4" long M6 bolts (larger than normal) connect both 72t sprockets at their center. They also bolt to the 24-tooth drive sprocket on the inside of the bottom bracket. This 24t chains up to the bike's 28t/14t cassette.

Normally, the 24t drive sprocket is suspended like a canoe outrigger. However, due to two engines twisting axially, I chose to use larger through-bolts and two freewheels. One ties to the pedal arm and outer 72t sprocket. The inside freewheel bolts to the in-board 24t sprocket, and to an adaptor that spins loosely onto the bottom bracket's axle.

It would've been simpler if I could've used a single serpentine belt and pulley system. You know, a 2" Chevy alternator pulley on each engine, with a $90 crank pulley from a Caterpillar tractor engine.
The flat 12" pulley could've been lightened via extensive machining and made to fit the bike's pedal arm, freewheel and axle. However, the gearboxes' 6-splined shafts are too short to fully support and mate with the Chevy's thick underdrive pulleys.

And they don't have an outboard support.

Each gearbox's output shaft would have to be removed, lengthened, have its splines removed and converted to outboard bearing support nose fabrication.

Serpentine or V-belt, this would need to be done.
A single chain with idler support and one driven 72t sprocket could possibly be configured. However, I like two separate chain systems. If one is misaligned or completely troublesome, or if one chain breaks, simply remove that chain and "limp home" on the other engine.
 
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5-7HEAVEN

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Well, using chains, sprockets and a freewheel seem like a simple way of connecting a small engine to the bike's bottom bracket(BB). Engineering two engines to hook up seems do-able, especially since no components need be custom made. Just drill matching holes between freewheels and sprockets, then assemble.

And don't forget to fab chainguards!!

This morning, I awakened with an ingenious manner of using timing belts and pulleys to connect twin engines with the bike's BB(Single engine installs can benefit too)!
1. Install a go kart's driven pulley to the freewheel on SBP's pedal arm. Instead of serpentine belt system, karters proved to use timing belts/cogs with 5mm/8mm/10mm pitch. Then install the driving pulley onto the jackshaft or engine's PTO.
Kart pulleys range from 9t(.90" overall diameter{OD}) on the driver pulley to 143 teeth(8.96" OD) w/5mm pitch teeth. They have a 5.25" bolt circle diameter(BCD). SBP's pocket bike freewheels' BCD is about 54mm, or 2.12" BCD. Obviously the freewheel won't bolt onto the kart pulley, so an adaptor has to be fabricated. Find any 6" OD or larger spare chainring sprocket with a solid core and a 2.12" BCD. Drill the sprocket with six holes in a 5.25" BCD, to accept 1/4-20 bolts. Then machine off the unwanted sprocket teeth.

Now you've made the adaptor to connect the large driven timing pulley to the BB's freewheel of your bicycle.
Using correctly-sized pulleys, a gear ratio as high as 15.89:1 can be attained.

You can attach the small driver sprocket to your jackshaft. If its inside diameter(ID) is too large, use a larger jack shaft diameter or an adaptor reducing bushing. Measure for appropriate length and buy the belt.

You'll probably need to use an idler system.

Now to fabricate an adaptor to install a timing pulley onto a small engine, using the 6-spline/13mm shaft on the pocket bike's 5:1 clockwise-spinning(CW) gearbox.

Using the 6-splined 5:1 gearbox produces spectacular gear ratio combinations. The 11t/72t T8F combo w/5:1 gearbox yields 32.73:1 gearing. Linked to a 34t/12t cassette, that's a stump-pulling 46.36:1 and cruising in final drive at 16.36:1.

Now with the go kart pulleys, gear ratios could be as low as 112.55:1 low and 39.72:1 cruising.
Wayy too low? Ok, choose bigger drive sprockets and smaller driven ones.
A 14t driver with a 90t driven pulley gets 45.54:1 First and 16.07:1 final drive.
Perfect for a high-winding/stump-pulling/hill climbing bike and city speed limits with a heavy rider.

The biggest hurdle of using serpentine or timing pulley systems is attaching the driver pulley to the 6-spline/13mm shaft on the 5:1 gearbox. After that, it's a simple matter of choosing the corresponding pulleys, belt and idler system.

Enter the go kart's driver/driven timing belt and pulleys.....race-proven, easy to find used and new, light and relatively inexpensive, with the correct gear ratio combinations!

Parts needed to adapt the go kart's driver/timing pulley onto the 5:1 pb gear box:
A $4 14t/T8F pocket bike sprocket from Ebay.
A $10 used 14t x 20mm x 8mm go kart drive pulley from Ebay.
Weld the two together; the go kart pulley now has a 6-splined center.
However, the machined groove and the snap ring on the gearbox's PTO(power take off), which secures the 14t sprocket is now inaccessible.
Disassemble the gearbox and remove the gear box's 6-spline PTO shaft.
See how delicate the gearbox's internal gears are!
Weld a 11mm or 7/16" shaft 3" long onto the splined end of the PTO. Be careful not to damage the splines.
Using 3 mounting bolts of the gearbox, fabricate a bearing support for a 1 5/8" OD bearing with a 7/16" ID.
Welding on the 11mm shaft and fabbing the bearing support are the only fabrication needed. Everything else is simple bolt on stuff.
Reinstall the PTO into the gearbox.
Bolt on the bearing support.
Trim the shaft and machine a groove for the new snap ring( or thread the shaft for an 11mm or 7/16 nut).

Voila! Using the proper length/width timing belt and idler pulley, the go kart pulley system can now bolt on and provide the correct gear ratio and connect to the BB of your bicycle's drive system.

Disclaimer: FWIW, this is all theoretical.
I haven't created it yet, because it's simpler for me to chain together TWO separate 11t 6-splined drivers to TWO separate 72t sprockets, then bolt it to TWO separate SBP freewheels and ONE 24T chainring sprocket, for a "V-twin" engine project.

It was MUCH simpler using a single engine and chaining ONE 11t cog, ONE 72t driven sprocket, ONE freewheel and a 24t chainring sprocket.

If all these chains and sprockets fail into one hot mess, then I'll try go kart timing belts and pulleys on my "V-twin" project.

But I'll still try to do the go kart pulleys on my Predator 212/shift kit project.

And that's another one on the burner.
 
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5-7HEAVEN

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Jun 22, 2007
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Well, I cancelled Harbor Freight's "indefinite backorder" and bought a 7HP clone.
It should arrive next week.
At least I won't be worrying about grenading the flywheel.
 
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