Twin Pocket Bike Engines Build

[5-7HEAVEN]

I've been working on my new project motorized bicycle for the past couple of months. The bike I build must be light enough for me to carry upstairs. My current ride, Snow Tiger, weighs 70lbs; it's no problem getting it into the loft.

I'm 70 years old, so my bikes have to be light enough for me to lift and carry a distance.

My current ride Snow Tiger(ST) weighs 70lbs.
My new project The Blue Twins weighs 61lbs. so far.
It'll end up a few pounds heavier than ST.


I'll post pics and share more.

I was installing a Tanaka 47R, ala mid-frame and shift kit.

Yesterday morning, the Tanaka was removed, making room for TWO pocket bike engines!!

Mid-frame twins with shift kit!

 

[5-7HEAVEN]

The engines I'll be using are 47-49cc pocket bike(PB) engines I had laying around for 10 years. I don't particularly care for them. I guess I'm prejudging PB mills(engines). I've heard they're loud and run dirty. I use a Tanaka engine on Snow Tiger, my motorized bicycle. It's powerful AND extremely reliable. Tanaka 47R 2.8hp engines are like thoroughbreds to me. Years ago, it was EXTREMELY difficult to find new ones, since that model's been discontinued. Mine were relatively expensive to purchase, but I haven't spent a dime on them on repairs since I bought them.

But two pocket bike engines, stacked like two slices of bread, fit my frame.

I tried fitting twin Tanakas in the midframe, but there's no room. I tried one Tanaka and a PB. There's no room for both in that space. I tried mounting the Tanaka in the midframe and the PB up high near the front top tubes. I have a spare Scooterguy engine mount that mounts small engines near the top tube. Neither engine fits well at the top tube of cruiser frames, because of the two smaller tubes arched below tit.

The configuration of one engine in the mid-frame and a totally different type of engine near the top tube looked odd. And that's a lot for me to say so.

Anyway, I placed two pocket bike engines inside the mid-frame.....
they fit like two slices of bread, with room in between to make a meatball sandwich!

Of course, in the final scheme, that meatball sandwich might turn out to be baloney and cheese, lol.

 

[5-7HEAVEN]

All right, so I have Snow Tiger, my Tanaka-powered Diamondback Response mb.

And I'll have The Blue Twins, my "other one".

I bought the prettier PB engine on Ebay. It was a custom project someone built, but never ran. It has an adjustable carb that I like. I ran it on friction drive for a few miles, then it quit. I think it's the spark, which I'll fix as time progresses.

The plain-Jane pocket bike engine was purchased as a curiosity piece. Both were literally door stops to the shop. They'll finally be put to good use.

The picture of my build is in the General Discussion section. I'm not good in posting pics. My son's coming over to help resize the photos I've taken. Then I'll post 'em.

This is only Day 2 of the twin-engine formatting. The rest of the bike's been slowly coming together, as time and $$ affords.

Basically, it's a frame-up build from a new old stock(NOS) Diamondback frame I found online. In fact, I get most of my parts from Ebay or other Internet vendors. I was happy to find a suspension fork for my 1" headset tube. It's an inexpensive $75 Suntour fork. Three things I need from my bicycles are engines, front suspension forks. And disc brakes, front and rear.

That's just me.

This is how I see my controls' layout on the handlebar:
Starting on the left, a twist throttle on the handlebar, controlling engine #1. That's the powerplant bolted under the top tube. One brake handle is on the left side, which controls both front and rear disc brakes.

Two kill switches will mount near the brake handle. There's one for each engine. Left switch kills engine#1; right switch kills engine #2, which is the powerplant on the bottom.

In the middle of the handlebar will be a simple generic bicycle speedometer. There might be a problem attaching the sensor to the Teny mag wheel. If the speedo doesn't work, it's not a bother. I MIGHT run up to 40mph on occasion, if the speed limit is 35mph.

I just need to get up to speed VERY quickly, lol. That's where twin engines provide the torque to push through stiff headwinds and inclines.

The right side of the handlebar won't be as busy. A twist throttle for engine #2, and a derailleur control for the Shimano 8-speed cassette. It'll probably be the "quick-shifter" Shimano model, like on Snow Tiger.

I like keeping things "same-same" on my bikes. Same 8-speed cassettes and shifter, same brakes, same gearing and sprockets(46.51:1 first gear and 15:1 in 8th gear), same Schwalbe Big Apple tires.

I'd love to run the same Tanaka engines, but they just.....won't.....fit.

 

[5-7HEAVEN]

This is how I intend to hook up a pair of pocket bike(PB) engines and a shift kit on The Blue Twins(the name I've given this mb):

Figuring out your gearing is THE most important mathematical calculation everyone using a motorized bicycle needs to do. If you miscalculate, you lose performance. Best-case scenario, your bike is fast, but it can go faster. Worst case scenario is you're geared too low and blow up your engine. Another bad-case scenario is your engine moves your bike VERY little or you burn your clutch out. My gearing needs are simple, after years of trial-and-error on Snow Tiger. It might not work for others. I'll keep mine the same on all my bikes. If there's a design change, it'll fit the next engine, whether it has 1hp or 10hp.

I always gear super low, with an emphasis of having a usable 8th gear. That way, you have the stump-puller to crawl around broken sidewalks and very steep parking ramps and hills. OTOH, you have a freeway gear, for those wanting to reach 50mph or have your engine purr at 40mph.

I like 50:1 in first gear to crawl around. Second and 3rd are also pretty low. On flat ground, I could actually use 3rd, 5th and 7th gear. More on that later.

Here are my sprocket choices and how I get close to 50:1. It's literally junior-high math:
Low gearing isn't easy to accomplish. Most cases need multiple jackshafts and sprockets. However, the ace-in-the-hole for small engines with 76mm clutches are the pocket bike transmissions and CVT boxes. They range from 3:1 to the 7:1. The beauty of it is that they all bolt on to provide an easier way to attain a low gear ratio.

I need 50:1 gearing. One PB transmission offers 5:1 gear reduction, which helps greatly.

It is EXTREMELY important to correctly identify which gear DRIVES and which gear is DRIVEN, when chained together. When dividing the numbers to calculate ratios, do NOT assume that the bigger number is ALWAYS divided by the smaller number. The exception to that rule is the relationship of the most-often times larger chainring DRIVE sprocket to the most-often times smaller DRIVEN cassette or rear wheel bicycle sprocket.

Great! My big DRIVEN sprocket on the BB has 72 teeth. My engine DRIVE sprocket sports 11 teeth. 72t/11t = 6.545:1.....

Soooo, 5:1(PB gearbox) X 6.545 = 32.725:1

I have no jackshaft to calculate, so it transfers directly to the DRIVEN gears on the cassette, divided by the DRIVE gear on the BB.

The DRIVE gear sprocket on my BB has 24 teeth.
The 8-speed cassette DRIVEN gears are 36-26-23-20-17-15-13-11.

Sooooo, 36t/24t = 1.417:1

Finally, 32.725 X 1.417 = 46.37:1.....good enough for me.
And the 8th gear with 11 teeth is 11t(DRIVEN)/24t(DRIVE).....
11/24 = .458:1
Annnnd 32.725 X .458 = 14.99:1 or 15:1.....

In perspective with China Girls' rear wheel sprocket.....
The Blue Twins will have a first gear similar to a China Girl's rear wheel sprocket having 113 teeth.
In 8th gear, it will be similar to a China Girl's 37-tooth wheel sprocket.

The best of both worlds.

 

[5-7HEAVEN]

I could fit a chain to each engine directly to the bottom bracket(BB).
The first engine sprocket, one chain to the BB sprocket. Done!
The second engine sprocket, another chain to its own BB sprocket. Done!
The freewheel on the pedal arm links both BB sprockets. One chain ring sprocket links to the 8-speed cassette. Done!

If I'm lucky, the chains and sprockets will be spaced 20mm from each other, and line up behind a single chain guard.

Right now, I'm using a 203mm(8") sealed bottom bracket. I hope I don't need a wider one. The next step up is a 330mm(13"!) unsealed unit.
I guess I could trim it down to 10" or so.

Orrr, I could run a jackshaft. Both engine chains converge on the right side, midway between engines and BB. Then a single chain runs to the single 72t sprocket on the BB.

The problem is that pocket bike engine sprockets I use are T8F chain-style. They have 6-spline 13mm pinion shafts. T8F sprockets are small, especially the tiny 11t drive sprocket. The #25 sprockets are even smaller. However, they get the job done. If not, the pocket bike industry would've swapped out to bigger chains and gears.

I could not find T8F sprockets that slip onto any conventional 1/2" or 3/4" shafts.
And I don't feel like having a 6-spline 13mm shaft 8" long fabricated.

My gut feeling says to run each engine directly to the bottom bracket(BB).
It's simpler and takes up less space. There's no need for a custom fabbed 6-splined jackshaft, bearings, supports, 3 more sprockets, set screws, locking collars, woodruff keys, lock-tite, maintenance and adjustments.

I'm sleeping on that decision. It'll be a short nap.

 

[dchevygod]

I understand why you would want to double up with those 2.nothing HP PB engines. Have you left the CY darkside? Fit a ported 460 on it and call it a day. 8 HP with a port and pipe will kill that dual engine setup that will maybe make 4.5 stock.

Just my opinion. On what chain setup to run id see if you could use just one chain and route it with idlers and a spring tensioner over both pinion gears. Rotation is going to be the challenge since you can't go over under the idler would hold the 8mm chain in a v shape in between the meat ball area then a tensioner for slack. While allowing more sprocket tooth engagement and keeping it all on one chain and bb sprocket.

Make my suggestion work so i can buy the spare 72t from you lol

 

[dchevygod]

Also to un-clutter the bars id look into a dual pull cable for one twist throttle. You know i hate the bars that have no space or flow at all. My controls are totally stock looking because i modified the left side shifter to be the thumb throttle. If anyone tries to steal my bike ive got a few extra seconds to tackle there butt while they search for a throttle lol.

Did you steal my pipe design? But use a better looking chrome pipe!

 

[5-7HEAVEN]

LOL, that X1 pipe was just to see if it'd somehow fit.

I've had twin engines before. The individual throttles were more versatile and easier to adjust. No need to synchronize engines/carbs.

Sometimes you'd want twins to show up to the party; sometimes you don't.

Yeah, the 460 has a lot of power. I've had that engine.

If its clutch problem could be licked, I'd jump on it again.

Or I'd run twin 460s.

That way, I could limp home on one engine, WHEN, not if, the clutch springs fail.

I chose twin PB mills partly for the shock value, and because they fit.

I do believe my chain setup will work.

However, I'll consider chevygod's suggestion of using a serpentine system with a single chain.

I'll have to practice "mechanical sympathy", so as not to destroy the drivetrain.

Maybe I'll need Grade 8 bolts at the bottom bracket.

I'll try the generic M5 hardware first.

 

[5-7HEAVEN]

Well, I did research on creating a serpentine drive system for this bicycle. The pulleys and belt ARE available thru a specialtycompany. Pulleys ALMOST fit. The 60-tooth BB pulley needs to be bored 59mm at the hub. Five 6mm bolt holes would surround the 59mm bore, in order to connect it to the flywheel.
For the PB trans sprockets, not so easy. The 6-spline pinion shafts are 13mm wide and slightly less than 16mm long. Besides machining for the splined shafts, the pulley would need to be counter-bored to accept the shaft's retaining C-clip.

And then there' s diagramming the serpentine layout, including the tensioners.

Methinks it's an outlay of about $300 to create the serpentine system.
Not worth it to me.
To use T8F chain and sprockets will cost.....
ZERO.
I already have all tha chains and sprockets. They cost less than $50.00.
It's a no-brainer.

 

[5-7HEAVEN]

As a chain guard for the PB sprockets and chains, I'm thinking a timing cover from a 1970s big-block Chevrolet(BBC) engine MIGHT fit!
I'll look for a used one to trial-fit it.

 

[xXNightRiderXx]

Well, this is interesting. Admittedly more interesting than Night Prowler. I was thinking, if you offset the top engine so its a bit more forward, you can still run a single chain. Just run it from the top engine, to the bottom engine, around the BB, and back up to the top engine. If you've already tried this, please disregard this suggestion.

 

[5-7HEAVEN]

Well, this is interesting. Admittedly more interesting than Night Prowler. I was thinking, if you offset the top engine so its a bit more forward, you can still run a single chain. Just run it from the top engine, to the bottom engine, around the BB, and back up to the top engine. If you've already tried this, please disregard this suggestion.

Each chain would have to wrap around the engine sprockets a goodly amount, much like the Chevy V8s' alternator belt wraps around the water pump, crank and alternator pulleys. I don't believe there's enough room in the midframe to position the engines in that layout you suggested.

 

[Ludwig II]

Tensioning such a length would be a hobby in itself.

 

[5-7HEAVEN]

Tensioning such a length would be a hobby in itself.

I was thinking that.

I entertained the idea of running a v-belt(Plan B) or a more effective serpentine pulley system(Plan C). However, since I already have everything to install a T8F pocket bike chain drive (Plan A), it makes sense for me to run the chain.

 

[5-7HEAVEN]

As a chain guard for the PB sprockets and chains, I'm thinking a timing cover from a 1970s big-block Chevrolet(BBC) engine MIGHT fit!
I'll look for a used one to trial-fit it.

Updated on 5-6-17:
I bought a new BBC timing cover for $15.00.
IT FITS LIKE A GLOVE!
The cover's upper hole lines up with the top engine's transmission's upper bolt. It completely covers both chains and chain ring sprockets.
I might drill lightening holes, or not.
I'm in sunny California for a month-long vacation. I'll see if my son can post a picture of the BBC cover mounted on my bike.
It looks BOSS!

Now I'm wondering if I should buy a chrome timing cover.

 

[Ludwig II]

If the cover''s plastic there are companies who will do vacuum plating of it.

 

[5-7HEAVEN]

Chrome parts for Chevy engines are cheap.
I can buy a BBC chrome timing cover for $20. I wasn't sure it would fit, so I bought the plain one, which I might drill lightening holes.

 

[Russell]

I'm 72, one of my builds weighs 85 lbs. Pulled my back flipping it over. Good part is my back reco
vered after a week! Keep rolling !

I've been working on my new project motorized bicycle for the past couple of months. The bike I build must be light enough for me to carry upstairs. My current ride, Snow Tiger, weighs 70lbs; it's no problem getting it into the loft.

I'm 70 years old, so my bikes have to be light enough for me to lift and carry a distance.

My current ride Snow Tiger(ST) weighs 70lbs.
My new project The Blue Twins weighs 61lbs. so far.
It'll end up a few pounds heavier than ST.


I'll post pics and share more.

I was installing a Tanaka 47R, ala mid-frame and shift kit.

Yesterday morning, the Tanaka was removed, making room for TWO pocket bike engines!!

Mid-frame twins with shift kit!

 

[5-7HEAVEN]

Thanks for the encouragement. My current ride Snow Tiger weighs 70lbs. I can easily push it up flights of stairs.....for now.

 

[Tony01]

You know, the 46cc goped motor with a pipe is friggin awesome. Don't need any gears or anything really.