Anyone try a modern giant build?

Felt faker frames are actually built for these engines and vibrations and aren't nearly as thin as standard aluminum frames. A felt faker isn't a bad choice if you make sure to check for cracks before rides. I preech steel because they are easy to make into what you want, and don't have a risk of cracking when rolling through a pot hole
 
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If you want to go custom frame use a pit bike engine, heres a build thread using one. https://motorbicycling.com/threads/latest-lunacy-honda-ct70-clone-build.36108/

Its steel but its a 29er cross country bike with a shift kit

I've got a shift kit lying around here and half a mind to use a torque sensing bottom bracket with it to have a gas build that can compete with a toseven dm01/cyc photon. but it would be a real pig unless I was counting grams on every component. And if I were counting grams I would go friction drive and a mechanical throttle.

As for aluminum mountain bikes, lowracer has done a couple:
Thread 'Pocket Bike Engine Project 3 (V Belt)' https://motoredbikes.com/threads/pocket-bike-engine-project-3-v-belt.35861/

Thread 'Tanaka PF-3300 V-Belt Drive w/Power Pipe' https://motoredbikes.com/threads/tanaka-pf-3300-v-belt-drive-w-power-pipe.36996/

I wont say vibration concerns are overblown, just that failure wont be instantaneous but should still be non destructively tested every so often. And that there are better options for weight savings or more up to date geometries.

Could always take a cheap steel frame and braze or weld a curving top tube on it.
 
If you want to go custom frame use a pit bike engine, heres a build thread using one. https://motorbicycling.com/threads/latest-lunacy-honda-ct70-clone-build.36108/

Its steel but its a 29er cross country bike with a shift kit

I've got a shift kit lying around here and half a mind to use a torque sensing bottom bracket with it to have a gas build that can compete with a toseven dm01/cyc photon. but it would be a real pig unless I was counting grams on every component. And if I were counting grams I would go friction drive and a mechanical throttle.

As for aluminum mountain bikes, lowracer has done a couple:
Thread 'Pocket Bike Engine Project 3 (V Belt)' https://motoredbikes.com/threads/pocket-bike-engine-project-3-v-belt.35861/

Thread 'Tanaka PF-3300 V-Belt Drive w/Power Pipe' https://motoredbikes.com/threads/tanaka-pf-3300-v-belt-drive-w-power-pipe.36996/

I wont say vibration concerns are overblown, just that failure wont be instantaneous but should still be non destructively tested every so often. And that there are better options for weight savings or more up to date geometries.

Could always take a cheap steel frame and braze or weld a curving top tube on it.

Pitbike/ct engines are part of the future builds. That's for sure.
 
Looks like a tight fit with that cross bar so low in the frame. With some perseverance you should be able to make it work.
I did some rough comparisons, and it should go straight in. I intend on using an offset intake, but it has the same geometry as my Gemini in the low triangle.

I wouldn't mind eventually going for a honda gx conversion, and in doing that i intend to keystone the frame anyway.
 
Like this or lengthening the frame? A drop loop could also work. The 1.1/8th really opens a lot of doors though. Same for the canti bosses on the rear, avoids having the sprocket and a disc brake so close. Grease on your rotor and abrasives on your chain, awesome!

 

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