The Skyhawk GT frame build

Dogtown Burner

Dogtown Burner

New Member
Ok, so here's the progress on the all aluminum in-frame-tank cruiser/Mtn hybrid. This frame is set up for MTB sizes, and can be made in any style. I chose to go with Board tracker turned Flat track. The style is definitely a culmination of components that make something unique and perhaps off beat- but thats my style. here is the initial setup in the unfinished (un-started) shop.

I chose to go with a solid triple tree front end, as I wanted a more solid front end than the monarks on my #3 racer. My plan was to go with Navy blue, like a Felt Slater, but it hasnt happened yet...
 

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buying this frame was exciting because I KNEW the engine would fit with little or no effort. and it would sit in the correct position for weight and balance! here, the idea of a radical pipe is rattling around loudly in my head, while my peers were telling me I was insane...
 

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Thankfully I had the strong support from my friends Rob and Greg at Piston Bikes. here we are in month 2, trying to figure out a drive solution, along with raer disc brake, and finding/making frame clearance in a frame not made for rear discs...

the sprocket adapter, sprocket, and disc rotor in these pictures did NOT wind up on the bike
 

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the question of sprocket width, top hat off set, teeth size, brake rotor width, caliper mounting ( we cant weld aluminum.) and a few other things were big stumpers. head scratchers. then I found a sticker to fit the model goal!
 

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then we got it working to ride while the engine was being built at the race shop...
 

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finally, after a few months of massaging, I got it all together with the help of Dave Rust. Dave Modified the pipe header, shape, and fitted it how i imagined it. true team work. his experience with motorcycle racing flat track was epic in this layout. notice the custom brake mount for the rear disc. talk about a pain in the a$$. but Dave pulled it off with only hours before the race. the race it won. we used a spacely sprockets 40 tooth which seems too bigl at this point. the engine is super torquey.
 

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and some finals...
 

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that is a really nice bike man im surprised the chain dosent touch the rear caliper when you ride its wicked close but with all the guys you had help you must have some clearance the pic dosent show.

also is it just me or did you guys take a chunk out of the CDI?
 
JonnyR said:
that is a really nice bike man im surprised the chain dosent touch the rear caliper when you ride its wicked close but with all the guys you had help you must have some clearance the pic dosent show.

also is it just me or did you guys take a chunk out of the CDI?
Click to expand...

our slogan was "AIRCRAFT TOLERANCES, GENTLEMEN!"

It was really the only option. there is no single speed rear disc hub with spoke flanges any narrower, so the issue is the rotor hitting the frame. very precise. if anyone knows of a single speed-disc-hub with narrower spoke flanges, there would be more space for the rotor to not hit the seat stay. (and no work to the CDI. photo tricks...)
 
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Bill in Oregon said:
Wow, that thing is a gem. It's as beautiful as a musical instrument.
Click to expand...

Thanks you! 6 months and a lot of staring... haha. Then my pal Dave Rust of Arrow motorized cycles put the icing on the cake with the intake, exhaust, and clutch mounts. his plasma cutter is really the life saver. as well as his amazing fabrication skills. we spent half a day fitting the pipe alone. the intake manifold took 3 tries. then Dave straight up made a rear brake caliper mount that fit with tolerances in the thousandths. with some teamwork and skill this bike went together, and now runs like a banshee!
 
I'm curious why you went with the 4 stroke frame vs the 2 stroke frame. The 2 stroke frame has built in engine mounts and reduces the wheel gap between the front tire and the frame. (In your 5th post, 3rd pic from the left the bike in the background with the black tires is a 2 stroke frame and you can see the differance between each bikes front tire to frame gaps).
 
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Dogtown Burner said:
Ok, so here's the progress on the all aluminum in-frame-tank cruiser/Mtn hybrid. This frame is set up for MTB sizes, and can be made in any style. I chose to go with Board tracker turned Flat track. The style is definitely a culmination of components that make something unique and perhaps off beat- but thats my style. here is the initial setup in the unfinished (un-started) shop.

I chose to go with a solid triple tree front end, as I wanted a more solid front end than the monarks on my #3 racer. My plan was to go with Navy blue, like a Felt Slater, but it hasnt happened yet...
Click to expand...


Hey what kind of muffler do u have?
 
JimsFelt66 said:
I'm curious why you went with the 4 stroke frame vs the 2 stroke frame. The 2 stroke frame has built in engine mounts and reduces the wheel gap between the front tire and the frame. (In your 5th post, 3rd pic from the left the bike in the background with the black tires is a 2 stroke frame and you can see the differance between each bikes front tire to frame gaps).
Click to expand...

It's not exclusively a
"4 stroke" frame. Notice the engine sits snugly in the V saddle. And front wheel distance? That's purely a cosmetic choice in frame style and has no impact or effect on performance.
 
jpanichella said:
How does that frame feel? Sturdy enough? I've been eyeing one of these up, instead of trying to salvage a craigslist bike.
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Haha really? Ya, go with the "salvaged Craig's list bike" over the aircraft aluminum 11lb in-frame tank set up for a triple braking system, HD MTb components,motor specific frame. See you at the finish line.
 
Dogtown Burner said:
Haha really? Ya, go with the "salvaged Craig's list bike" over the aircraft aluminum 11lb in-frame tank set up for a triple braking system, HD MTb components,motor specific frame. See you at the finish line.
Click to expand...

Well, I've had one of these bikes break on me (shear the downtube in half) under speed. I was planning on either keeping my eye out for a vintage Chicago schwinn/worksman frame or maybe taking the Skyhawk frame rout, but I've heard of people having issues with aluminum frames cracking on them. So consider me a little cautious.
 
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jpanichella said:
Well, I've had one of these bikes break on me (shear the downtube in half) under speed. I was planning on either keeping my eye out for a vintage Chicago schwinn/worksman frame or maybe taking the Skyhawk frame rout, but I've heard of people having issues with aluminum frames cracking on them. So consider me a little cautious.
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One of "these"? Bikes. Which bike? Grammatically it would seem you mean the sky hawk frame. But I'm guessing you mean the random Craig's lister/50 year old frame. I cant believe im typing this, but yes, Be wary of cheap aluminum bike frames and 60 year old bikes not intended for use with engines. Perhaps the heavy duty aircraft grade aluminum frame built by the engine manufacturer would be a better call. Good luck. dance1
 
Dogtown Burner said:
Perhaps the heavy duty aircraft grade aluminum frame built by the engine manufacturer would be a better call. Good luck. dance1
Click to expand...

Not sure about who makes the frame, but we know that Grubee does not actually make the motor, just imports them.

And I really want a frame that is much higher quality than a Grubee (or any HT) 2 stroke, lol.

That being said, I love the build, I think it looks great! Excellent work.
 
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