Skyhawk frame build / thoughts

Discussion in 'Motorized Bicycle Welding, Fabrication and Paintin' started by Agreen, Apr 18, 2015.

  1. Agreen

    Agreen Member

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    I just got my Skyhawk aluminum frame in yesterday and started piecing the bike together. I thought I could just transfer over everything I have from 1 or 2 of my existing bikes, but I was seriously wrong...

    Let me just start by saying that I'm not a bicycle mechanic. I have worked in the automotive industry as a technician for many years, and joined the Navy since, and I now work on reactor electrical systems.

    So when the kit came in I figured it would be easy to just piece the bike together and get it mocked up the way I wanted it, tear it back down and powder coat everything, and be done before the day was over. I got almost nowhere.

    The idea I had in my mind was something simple and pleasing to look at. Rigid, curved forks, rim brakes up front, coaster drum brake in the back, single speed, fat tires, satin black with huge white walls. A very classic look.

    I started with the forks. I have several donor bikes. A ladies' Schwinn Del Mar, an old huffy free spirit (from like '97?) a Schwinn mountain bike, and a cranbrook-esque bike that says "good vibrations" on the chain guard. I decided that "good vibrations" is in too good of shape to tear apart, so I'd leave it alone. The free spirit is rickety as he11 and I also wanted to have a single speed, so that ruled it out twice, along with the Schwinn mtn bike. So I start dismantling the Del Mar. Lo and behold, the damn forks don't fit. I knew I needed 1-1/8" steer tube forks, and this one is 1". So I figured I could find 1-1/8" OD tubing at a hardware store and cut/weld a new steer tube... nope. Check. Bike stores? Maybe they have a solution? Every single one said I HAVE to get 1-1/8" threadless forks. But nobody had any! And (apparently) finding 1-1/8" threadless, rigid, and curved forks is going to be hard to do. Long story short, turns out they're liars and I don't need threadless, they just wanted me to spend the extra money. I even bought a stem from one shop thinking I'd need it when I finally find those "rare" forks. I put the suspension forks from the mtn bike on and they fit just fine. Only a little short, so I'm going to cut the steer tube in half and extend it 20mm with the 1" steer tube I cut off the Del Mar. Liars...

    More pictures to come as I actually get work done.
     

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    #1 Agreen, Apr 18, 2015
    Last edited: Apr 18, 2015
  2. Agreen

    Agreen Member

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    Here's another thought or two:

    Don't buy the fuel shutoff valve when you order the frame. (Got it from gasbike, BTW). It's the same valve you get in the motor kit.

    What's the biggest tires I can put on these mtn bike rims? The rims measure 0.975" on the outside. 26" dia.
     
    #2 Agreen, Apr 18, 2015
    Last edited: Apr 18, 2015
  3. bluegoatwoods

    bluegoatwoods Active Member

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    Hmmmm.......well, I read this thread last night. And I didn't answer it because I simply didn't have any answers. But the answer you've now received is kinda hard to understand.

    So the rest of us had better try to come up with something.

    Those rims measure .975, eh? I'll guess that a 1 1/2 or 1 3/4 tire is recommended. I think I'd still try, though, to squeeze in a 2.125. Simply because you want just as much tire as you can possibly get.

    Keep us posted, will you? That Skyhawk frame is interesting.
     
  4. Agreen

    Agreen Member

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    Mmm, yes. Very interesting indeed lol

    The mtn bike wheels are the best ones. The del mar rims are about 1" out of round by my dial indicator, so i doubt any amount of truing would be useful at this point. The tires that are currently on there are 1.9 something (not currently looking at it). I figure i could try squeezing on a 2.125 from the del mar. If it works, great. If not, oh well. I was really hpping for at least a 2.35, but that's probably pushing it.

    I'm plannimg on finishing the forks today and will probably be riding it later this afternoon if all goes well. Then the process of tearing it back down for powder coating will ensue. The motor is supposed to come in tomorrow!
     
  5. indian22

    indian22 Well-Known Member

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    Hi, 26" x 2.125" rims will clear forks and frame with Fat Fanks "Schawalbe" 2.351" front & rear Fat Franks are a tall tire and clear my Rock Shox mountainbike suspension tire vertically with one half inch to spare. The same tire clears the fork side to side by about 3/8" on each side. Where it gets tricky is at the rear. The fat Franks clear the rear "fender brace support" also by about 1/2" ....many of us don't care for front or rear fenders on most of our builds because of past epic wrecks caused by fender/tire lockup. The Grubee frame design isn't very fender friendly with larger tires, I don't think fenders are a good idea on this frame especially with large tires & wheels. The Skyhawk Grubee frame takes a bit of work to accept a wide tire on the rear, chain contact with the wide tire is to be expected on both the pedal drive side and the motor drive side, with wheel & tire sizes over 1.75" wheel & 1.95" tire. Also remember a wider wheel mounted with a narrow tire makes the tire flare out, looking much larger cause it requires more space.

    Photos of my Skyhawk Indian Navaho build can be seen on the Vintage bike/ Board track sub-forum of this site. Titled "Indian sabor/flavor". I used a modified Grubee GT 5 66cc for this build & don't have chain to tire contact problems with the larger wheels and tires mentioned earlier & with about a 100 hrs now total on the frame & 3 motors (I use this bike to break in engines for the other bikes I build) so I'm pretty certain the combo presented here works. I even ran a rear "bobbed rear fender" for awhile till noticing it was rubbing TDC!
    To gain pedal side chain to tire clearence I installed a 3 piece 68mm bottom bracket x 105mm cartridge in a Euro style conversion kit that fits into the 2" american style bracket shell that the Skyhawk is designed with . If a bit more room is necessary I use frame spacer washers on the axle to keep the chain from rubbing the frame. Remember that most changes to a bikes drive line will effect other relationships. Tire centered, chain lines not staight, wheel & tire cocked, parts rubbing etc. I use a 2 piece Manic style hub to sprocket adaptor & coaster brake with a 2" center sprocket hole to allow the bent coaster brake lever to clear the sprocket & an axle spacer washer to help clear the frame. It's all pretty tight clearance, but no chain rub. It's not rocket science, but making everything work correctly while fitting more robust parts can be a challenge & you won't often just stumble into satifactory solutions.

    I'm certain that I could go with a bit larger tires on my Skyhawk probably 2.5" but any larger would test my day to day patience to the point of not enjoying my build and since I use multiple motors on this frame it wouldn't be worth going any larger. Check the photos on the suggested thread.
     
  6. indian22

    indian22 Well-Known Member

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    Couple of shots with the Fat Franks mounted on the Grubee Skyhawk frame...rear fender mounted (not recommended). RC
     

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  7. Agreen

    Agreen Member

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    No fenders are planned for that exact reason. The ones that came off the Del Mar just feel cheap and flimsy, and if for no other reason, I wouldn't use them based on that alone.
    That bike looks awesome Indian. Such detail! And yet, still quite simple. I'm not a fan of busy-looking bikes. I'm all about keeping things simple. Let the craftsmanship speak for itself.
     
  8. Agreen

    Agreen Member

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    After some very VERY meticulous measuring and tack welding (repeat) i got the forks extended. It took more time verifying the tube was straight than the actual welding. It's straight though!

    Gotta get to a computer to resize the picture...

    A new question popped up though. Why us the seat post so big? It measures about 1.075". All my seat posts flop around in there. Think "hotdog in a hallway".

    One seat post measures 0.955", and the other is 1.000". Still 0.075" of free play with the biggest one, and that's still a lot. We're not talking horseshoes or hand grenades here!
     
    #8 Agreen, Apr 19, 2015
    Last edited: Apr 19, 2015
  9. Agreen

    Agreen Member

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    Picture:
    Need to add words so i can post it lol
     

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  10. indian22

    indian22 Well-Known Member

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    If you want to use a smaller post you can buy a seat post shim, ebay etc. measure your seat post diameter in mm & the frames seat tube (inside dimension) in mm. Many different sizes of tubes used in bikes over the years, you could also just buy the correct post, 6 of one...half a dozen the other.
     
  11. Agreen

    Agreen Member

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    I'm finding this to be true. A lot.

    I'll make my own shim. Not waiting on shipping any more. I'm so tired of waiting all the time!

    Next question:

    Can i convert the mtn bike rear wheel to a single speed? Like take the cassette off and install a single gear? I don't care if i lose the coaster brake. I have studs on the frame for v-brakes, and it would look stupid if I just left them there.
     
  12. Agreen

    Agreen Member

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    Coming along sooo slowly.
     

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  13. knightscape

    knightscape Member

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    You said you've got your fork figured out, but i'll just post this for info. You can absolutely use a 1" steerer on a 1 1/8" tube, you just need a reducer like this:
    http://www.niagaracycle.com/categor...tube-reducer?gclid=COSvn6Cwg8UCFUMV7AodRF4AFg
    I'm surprised a shop wouldn't have recommended that. You would just need to bring over the 1" headset from the other bike as well. They may have said you have to use a 1 1/8" threadless because that's what headset that comes with the GT2a.

    As for tires, on my GT2a-s I've got 2.3" Duro cruiser tires mounted on DH39 rims which are 1.5" wide. Chain clearance is an issue, don't think I could get away with any wider without moving the engine outboard. I have a couple telltale grease marks on my sidewalls. I am running a 4 stroke though so sprocket placement might be different than yours.
     
  14. knightscape

    knightscape Member

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    The seatpost is 27.2mm, that's a pretty common modern standard for aluminum frames.

    You can convert the mtn bike hub to single speed, there are 2 different kinds, freewheel and cassette. Which have you got? The process is different depending what you've got, and it does require a special tool to remove the clusters usually, unless you want to get creative.

    I'm running a coaster on mine, you can space the axle out to 135mm if you have enough axle. There are 2 methods for this as well, you either add spacers inside or outside the locknuts. You just need 12.5 mm of spacers on each side.

    Inside locknuts (preferred):
    [​IMG]

    Outside locknuts:
    [​IMG]
     
  15. Agreen

    Agreen Member

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    I will assume it's a freewheel, based on the fact that it says freewheel right on it :)

    So what's the process? I'm pretty creative lol.
     
  16. Agreen

    Agreen Member

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    Oops, forgot to post the picture.

    Pretty rusty. Would much rather use the single speed from the Del Mar.
     

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  17. knightscape

    knightscape Member

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    Yowza, that's pretty crusty. You need a splined frewheel removal tool to thread that off of the hub, it loosens counterclockwise. IF you get that off of there, you can thread on a BMX freewheel. Some freewheels can be disassembled and reassembled, looks like this one isn't serviceable if those are two rivets I see in the smallest ring. Also, if it's that rusty, what do the bearings and races look like in that hub?

    If you'd rather use the coaster, as long as your axle is long enough to have 135mm of axle between the locknuts and still get threads on the outer locknuts, you're good to add spacers which can be anything from a stack of washers to custom billet 12.5mm purpose made spacers. Might also be easier and cheaper than messing with that freewheel. That part ain't rocket science, you just thread off the locknuts, add spacers to each side and then tighten them back down carefully so as not to bind the bearings.
     
  18. Agreen

    Agreen Member

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    A BMX freewheel... very interesting. I'll look in to that. The bearings are fine. The bike it came off just sat outside a little too long. I looked at the bearings and races. They look new, acually. The guy i got it from said he bought it 5 years ago and only rode it a couple of times. No bent rims, good bearings, only a little rust. Even the crustiness is surface rust. Comes right off. Still not going to use it though.
     
  19. Agreen

    Agreen Member

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    Done for the night:
     

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  20. Agreen

    Agreen Member

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    Nothing new on the bike yet. I got the 48cc engine kit yesterday and decided to tear it down to clean it before i started it. Glad i did. There are metal shavings all inside it. I was suspicious of the last one i got when i did a teardown after a couple runs and found scoring on the cylinder walls. So this time I'm doing it right...

    However, i cant seem to get the case to separate. I have it down to where the case is starting to separate, all 7 screws that hold it together are out. It just seems like the case is stuck inside somehow.

    I did see in this video:
    http://m.youtube.com/watch?v=FSHkKZArN-Y
    That the whole clutch shaft comes out. Cant seem to figure that out though. It's still in there, and it seems like its getting caught up on it.
     

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