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Mijimobile

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Dan Hunter

Guest
As I stated in the introduction, this project started with my desire to get my daughter a gas-powered scooter. I settled on a Visa Viper as I liked the chain drive and the simplicity of their gearbox along with the Honda engine option. While in Korea on a one year remote, I watched a gentleman washing client cars on base. His transportation was a bicycle with a friction drive engine on the front tire. I wanted to build a bike with the Visa gearbox/engine combination but had a more integral appearance. I spent a bunch of time researching part combinations and measurements until I couldn’t think it through any further.

I got back to the states and just couldn’t let it alone. I started acquiring parts for events…birthday, Christmas, whatever. It took a while and my wife was fairly certain it wasn’t going to happen. With all the parts accumulated, I started cutting frame parts and taping them together to make sure the geometry was correct. The intent was to allow the engine to be serviced without removal, driving a rather long wheelbase. The frame was MIG welded together. Much of it was free handed with lots of eyeballing and measuring. The lower portion of the frame was absurdly over-engineered; I have the steel in the garage for a second frame which will use an aluminum adapter plate and bungs on the frame to simplify the process and lighten the frame.

The steel was purchased at Aircraft Spruce. They cut to reasonable lengths for shipping and offer a large selection. That’s an Brooks B17 English leather riding saddle; based on the price, they were rather proud of it. I purchased a 68mm bottom bracket from Gaerlin in California along with the True Temper head tube and Surly dropouts for the rear axle. The Surleys are great because they allow you to adjust the chain tension with fore/aft axle shift. If I could find Answer BMX parts I used them as they made solid quality parts for a reasonable price. I used short Dotek crank arms as the pedals were only to get it moving so I wouldn’t smoke the clutch. I purchased a previous year model Manitou fork for a massive discount. Note it’s a disc only fork. The original brake was a Hayes unit but the lousy thing wouldn’t seal (cheesy design) so I replaced it with a Shimano Deore mechanical brake that works just fine. A key part of the bike is the Staton-Inc hub that allows me to drive on the right side with the pedals and the left side with the engine using an ACS Southpaw. The hub is also over-engineered with four bearings. I had Dave ship the hub directly to Gaerlan and they laced it up to some Sun Rhinolite wheels and slick high pressure Kenda tires to keep the rolling resistance down. That’s also where I sourced the Shimano Deore hub for the front disc. I modified a two finger front brake lever to pull the throttle cable and put the disc brake on the left grip.

The performance is pretty much what I expected. Because left side freewheels are in little demand, there’s equally little choice in tooth count and as it stands, my gear reduction is about 15:1. The engine just isn’t getting a chance to operate at a high enough rpm to take full advantage of the available power. My daughter doesn’t know the difference and operates it at real speed. I weigh about 225 and it’ll hold 22 mph but struggles into headwinds common in Oklahoma. If I could have attained 21:1 or so, I think could have gone with a 24” wheel instead of the 20” wheels and probably done better at targeting a good rpm. I’m looking at swapping Staton hubs and locking a fixed Azusa sprocket which should settle the issue. Also, I’m looking to replace the water bottle fuel tank with a chromed aluminum tank similar to those used as extended range tanks for motorcycles. I’ll probably just pay for a custom one with integral mounts and an offset fuel fill to allow me to mount it underneath the toprail.

It’s been a lot of fun to assemble but mostly satisfying to take from concept to reality.
 

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Alaskavan

Guest
Thanks Dan. Your expanded description answered some questions I didn't bother asking in my PM. Sure is a pretty bike.
 
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gone_fishin

Guest
what a beauty build...it looks huge until you see it with a rider.

close-ups of the engine and drivetrain, please?
 
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Dan Hunter

Guest
Sure, it's dark. Tomorrow OK? Don't mind the scars; it gets ridden fairly hard by my daughter and her nieces/nephews.
 
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5-7HEAVEN

Guest
:cool:say, Dan...that's a NICE bike!

what kind of engine and sprockets are you using?

not meaning to disrespect your creation, but methinks you have way less than the gear ratio you stated. if you are using STATON'S left sprocket, it MIGHT have 18 teeth. using a 9-tooth engine sprocket, that would explain why your engine is not attaining optimum rpm range.

can you give us some engine/drivetrain pix and gear reduction specs of the VIZA transmission?

FWIW, a 15:1 ratio would be like a happy time engine with a 36-tooth rear sprocket.(happy time engines have gear reduction of 4.15. combined with rear sprocket for a ratio of 14.94:1.) top speed would be in the high-30's mph.

if your gear reduction box has a 7.5:1 ratio, you will have 15:1 with your 9-tooth front sprocket and 18t rear sprocket. any ratio less than 7.5:1 would explain why your bike's performance is not at its best.

when you gear it correctly, you'll be afraid to let your daughter and grandnieces ride your bike.:eek:

again i say with humility, i am definitely not trying to disrespect you or your creation.

Myron
 
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Dan Hunter

Guest
Yeah, I'd have to go out and count the teeth but I believe the front tooth is 8 and the rear...geez, I guess I'll have to count 'em tomorrow. Fire away, as I pointed out - at 225, I've got some thick skin...well, and lard but I'm sure you're right come to think about it. Maybe it's that I needed 15:1 to get the 24" tires. It's been a while and I've been working other projects. My present is I'm converting an old riding mower to a dedicated sprayer platform that started with a remotor and a 100 percent horsepower increase.

Ok, I had to look. I'm actually getting 10:1 reduction.
 
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5-7HEAVEN

Guest
:cool:Dan, thanks for being cool.

on the VIZA website, the transmission's exploded diagram shows a 9-tooth engine sprocket. they're kinda secretive about their patented gear box.

STATON has a 16-t or 18t left-side freewheel sprocket. that would explain why your engine isn't reaching its potential.

hypothetically, if your gear reduction box is 5:1, your 9t engine sprocket and 18t rear gear calculates to 10:1. that would be similar to a happy time engine and a 24t REAR sprocket!

you would need a 27-tooth rear sprocket, which would calculate to 15:1 and top end speeds of high-30's mph.

for more low end and high 20's, use a 33-tooth rear sprocket.

FWIW, your 27t would be similar to happy time engine w/36t sprocket.
your 33t would be similar to happy time engine w/44t sprocket.

of course, all calculations are if you have a 5:1 gear box.

Myron
 
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Dockspa1

Guest
Hey Myron, That tire size would make a gargantuan difference in top and low end, Correct?
Doc
 
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5-7HEAVEN

Guest
:cool:Doc, i presume that 24" tires would yield higher speeds, and 20" wheels would have better low end.

too bad that STATON doesn't have left-side freewheeling sprockets with more teeth.

if Dan had 24" tires, his performance would be even more sluggish than what it is now.

i have a 20" DAHON with 18.75:1 rear drive. it is all low end, and my bike would benefit from a bigger sprocket.

Myron
 
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