DIY Shift Kit Project--'The Shifty Beast'

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lowracer

lowracer

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Oct 17, 2008
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This bike has morphed into many different motorized projects. It was only a matter of time before I experimented with a shift kit. I got all the parts I need now & have officially begun the install.
I ordered cranks, small chainring and wide BB from Sick Bike Parts. I had the ACS Crossfire freewheel and 104 BCD adaptor.
Originally I thought I'd have to mount the engine behind the seat, but yesterday I held up the Tanaka 47r w/PB transmission & I may have just enough clearance all around to mount in-frame. I won't be drilling any holes in the bicycle or welding...I always build with the notion that I may want to go back to an unmotored bicycle one day.
Here are the 1st few pics with the BB and freewheel cranks installed.
Cheers,
-Lowracer-
 

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lowracer

lowracer

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Gear ratios & speeds are as follows:
12T-44T
24T-9 speed cluster
8625 rpm's-26" wheel diameter-5:1 PB transmission
--------------------------------------------------
34T=25 mph
30T=29 mph
26T=33 mph
23T=38 mph
20T=43 mph
17T=51 mph
15T
13T
11T
 
Dan

Dan

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May 25, 2008
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Great name, Lowracer. (In pirate accent; "Arghh, a Shifty Beast)

Does "PB" stand for pocket bike?
 
16v4nrbrgr

16v4nrbrgr

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I can't wait to hear how it works out, I've been slowly getting a shifter together and hope it works out well enough gearing wise. Like yours, I'm gonna have a bunch of overdrive gears lol. Its cool how you've taken that great downhill frame and tried a bunch of different fast configurations, the shifter should be king for sure.
 
lowracer

lowracer

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Dan, yeah PB is for pocket bike. Funny you said that about Pirates, I was watching Pirates of the Caribbean 4 last night.
Wheelbender, Thanks I do hope it works out well.
16V, A shift kit seems like a good idea especially when using a high quality Japanese engine.
I believe a top notch Downhill MTB is the best platform to motorize. With strong frames, wheels, brakes & huge suspension travel designed to handle racing down mountains offroad. I just swap tires to slicks & add a power source. Many used DH MTB's are available for under $1000 (just look out for the abused)...Check out Pinkbike.com
-Lowracer-
 
16v4nrbrgr

16v4nrbrgr

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I wish I could find a brand new reeded Japanese pocket bike engine for less than $600 it would be great.

It's too bad that all I can afford is cheap Chinese crap, and manage to make it work well. People always will look down on the Chinese stuff.
 
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lowracer

lowracer

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zippinaround,
I will try to mount it in-frame (slightly left of frame).
If clearance becomes a problem, I'll either buy a wider bottom bracket or mount the engine behind the seat on a rack.
I'll try to get started on mounting it this weekend if time permits.
-Lowracer-
 
Z

zippinaround

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Aug 10, 2013
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would also like to know what exactly you did to make the cranks freewheel? what exactly do i need to do this? beside a engine and pb trans.
 
Z

zippinaround

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oh you just bought a kit? i thought you made it yourself.is it possible to just buy a freewheel and attach it to the chainring already on a mountainbike and drive that with the engine? i dont know anything about shift kits!
 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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16v, I don't look down on the chinese engines so much as I do the materials and assembly they use. Some of the pocket bikes are very cool designs executed poorly.
That's the price we pay for being able to afford to play.
Very few people could afford to play if the japanese were the only source of bicycle engines, and even the chinese small engines are beating the japanese in sales, though the japanese engines are much better built and more durable.
Much as I love the yamahondasakizuki's, I love the chinese even more because I can have more of them for less cost.
I may complain, but I wouldn't trade my chinagirl for anything.
This looks great so far!
I'm following the build even though I'll never buy a $1k bicycle. Ever.
.
 
Wild Bill

Wild Bill

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maniac57 said:
16v, I don't look down on the chinese engines so much as I do the materials and assembly they use. Some of the pocket bikes are very cool designs executed poorly.
That's the price we pay for being able to afford to play.
Very few people could afford to play if the japanese were the only source of bicycle engines, and even the chinese small engines are beating the japanese in sales, though the japanese engines are much better built and more durable.
Much as I love the yamahondasakizuki's, I love the chinese even more because I can have more of them for less cost.
I may complain, but I wouldn't trade my chinagirl for anything.
This looks great so far!
I'm following the build even though I'll never buy a $1k bicycle. Ever.
.
Click to expand...
I agree with all that but I will splurge on a rare occasion like I did on both my builds for the frame, and my second build would have never happened if not for the KTM clone. Its still a $500 engine but a genuine KTM would have cost a fortune new.
 
maniac57

maniac57

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Oct 8, 2011
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Well, these days, the extra expense of better hardware really doesn't make sense for me.
I'm perfectly content running around for pennies a mile at 25-30 mph all day long. The better bullets don't appeal to me enough to justify the outlay. I thought long and hard on a KTM or Morini build but in the end, why buy a high-speed high-dollar engine when all I'm doing is putting around? I need 11hp like I need an elbow in my forehead.
I'll just keep bench racing the s-5's and the 212 preds while pounding out the miles for under $300 bucks (so far)
 
lowracer

lowracer

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zippin,
Its not a 'kit'. The kits are produced specifically for the chinagirl engines and incorporate a jackshaft that bolts to the seattube. My setup is more like the old 'Scooterguy' mounting than the kits available today. The big difference though is that I wont drill holes through my frame to mount the PB transmission & fuel tank (as most scooterguys are mounted)
You would need the special front freewheel cranks (threaded shoulder on drive side crank) to accomplish the mission.
-Lowracer-
 
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lowracer

lowracer

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Zippin,
Yes, those two items, some chainrings and hardware. Then you need to mount your transmission/engine using some flat or angle iron stock.
-Lowracer-
 
lowracer

lowracer

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I know it isn't much, but I got the mounting figured out after a few hours of vice gripping aluminum bar and holding up my engine & trans. Looks like there is enough clearance to mount it in frame kinda like the 'Scooterguy' setup. The seat post tube/ rear shock strut has 2 nice flat aluminum plates with holes already furnished...I just need to bolt some aluminum bar to mount the transmission which will also hold the engine. Here is a pic with the vice grips holding the 1st piece of aluminum into place.
Cheers,
-Lowracer-
 

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Pablo

Pablo

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