2008 Specialized Fatboy Conversion


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9:06 AM
Mar 6, 2008
Just picked up this jewel this weekend. Plan on cutting the downtube(seat frame tube) from the bottom bracket and pivoting it about 1 foot further back to accomodate for the motor. Going to weld up all the vent holes and cable routing holes in the faux tank part and just use it for my gas tank(plenty of volume, maybe 1 gallon). I'll document the conversion for all that want to see how to do it.<br>
<img src="http://www.bikepedia.com/Helpers/readImage.aspx?filename=2008-Specialized-Fatboy-Ti.jpg">
<img src="http://www.motoredbikes.com/attachment.php?attachmentid=9107&d=1216042565">


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man, you gonna cut up a 1800$ bike ?
you'll need to offset the engine quite a bit to clear the HUGE back tire as well :D
the local LBS has one on display...I drool all over it every time I go :LOL:
Sure, why not? Its a lot more fun to ride with an engine:)
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Nice bike

You could save yourself some cutting by setting it up like this.


That frame would be perfect for this mod. Weld another bottom bracket into the frame just behind the seatpost. Then you could use a quality motor too. The Robin 35, Mit 43, or Honda 50. Look at my build for Zack. You will have to get a wider crank to clear the motor but you can get a Grube wide crank for 50$ & only extend it on the right side like this.

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would any of those motors fit in that small space behind the seat post? also, do you have to use some sort of freewheel crank? Will normal bicycle chain be strong enough to drive bike or will it snap? Could you draw a little picture on top of my picture of what you have in mind for the mounting? Can you post link to your build for Zack?
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Here is the original thread. This bike has gone through some more mods but the drivetrain remains the same.


This is another frame a lot like yours but a lot easier to modify than from scratch. I think any of these motors will fit forward of your seatpost.


The only mod on this frame was the extra b bracket & motor/gearbox mounts.
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Which motor do you think will fit the best? Also, where is the best plact to buy all the sprockets stuff? Thanks for your advice:)

The two strokes are the narrowest. I put a 4 stroke Robin on another bike like this & had to widen the crank on both sides. You can't go wrong with a Mit 43. Zack has a GP 460 now, but if I were starting over I would use the Honda 50, & deal with the width issue with a wider crank. You could use a HT, but after spending 1800 for the bike, why not do it proper? A HT motor is definately the narrowest, but the kit will not fit your bikes frame, and you will have to sacrifice that nice rear disk brake. So you're in for some mods no matter which direction you take. I like FRAME MOUNTS. Your bike deserves a nice one.

Again - sorry if I offended any of you HT fans out there. But I'm not a fan..............................
I spent a lot less than $1800 for the bike i have....I'd shoot myself if I spent that much on this bike.....I really like the way you did the other bike......I'll take more pics of mine around the seat post when i get home to get your advice on where to put the 2nd bottom bracket with the jackshaft.

If you do choose to go with a HT - that jackshaft kit that GhostO has looks like it uses a lot of the same components that I use & it would be an easier install. I just looked at the specs . Your bike is Aluminum. welding another bottom bracket will be a trick. Can you weld AL? If so then it is possible. It also has a 3 piece crank. The Grubee wide one piece crank won't work on that because your front bottom bracket is smaller in diameter. Are you going to install gears? All these things must be considered before committing to a finished design. I posted before I looked at your bikes man. specs. Sorry bout that. I can't weld AL or I would build one of these too. Very good start for a motored. I really like the way this bike is made.
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