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(ORBO) BACK40 by LTJ, design by OJ. (ROLLING! But withdrawing from the build-off.)

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22778748637_314007dabf_c.jpg


Been planning this build for a while...

Always loved the idea of those Redline Monocog bikes and Electra MOTO, a sort of rigid frame MTB with disc brakes crossed with a modern BMX single speed:

24092642596_a58533077c_z.jpg


22923743624_de32f55147_z.jpg


Those are cool bikes, but possibly a bit too modern and hip for me, needs a more retro frame and taller Klunker style bars, while I am at it I may as well upgrade the discs to full 203mm front and rear, upgrade the hubs to full heavy duty 48 spoke BMX trick bike, 14mm axle, sealed bearing units, and change the cranks to BMX 3 piece to match, maybe sliding drops on the rear with integrated disc calliper mount...

And that was as far as I got until I started talking to @OddJob, turns out this dude knows his stuff! He mentioned that he would be out of this build-off due to prior commitments and when I mentioned I would be doing 2 builds, he jokingly suggested I name one after him, well, I named it after his new bike shed: BACK40 Bikes!
He helped me refine the bike idea to give it some cool details and make it a much better bike to ride, mainly due to having incredibly short chainstays to help it change direction better and make it a fun "Chuckable" bike.

Here is the build board:

23933015972_9ea2130884_z.jpg


Those chain stays measure out at 14", which is as far as I could go due to the 26x2.5 Kenda Nevegal tires measuring out to 27"!

23552141245_bbb18d3aa1_z.jpg


23184303839_c82f967969_z.jpg


Of course the biggest problem with my plan is that nobody makes 14mm axled 48 spoke hubs with a disc mount... But they do make these:

22809051823_c2f207ceb9_z.jpg


Which means if I use a flip flop BMX hub for the rear and a standard rear on the front, I can do this:

23353660331_88db6a6bda_z.jpg


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Of course that means I will be using the small 'metric' side of the flip flop hub for the freewheel, which means I can drop to a 14 tooth freewheel, allowing me to drop the front to a tiny 30 tooth! Picked up a TuffNeck 30 for the front:

22878926130_73f3b7f8b7.jpg


Other big issue is finding 26" rims with 48 spoke holes! I searched hard for them, and even searched for undrilled ones, but the only ones I found were super expensive, until I looked at an add on eBay for a closing down bike shop, there was one line at the end that said: "We have these tandem rims in 48 spoke too, please enquire" I ended up with 2 tandem weight rated, 48 spoke, double wall, eyeletted rims for peanuts!

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Not sure yet if I will use one of my bargain Gyes saddles yet on it, but it may happen:

24051636326_086837bf87_z.jpg
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Anyway, that is as far as I have gotten, need to start throwing sparks and spoking rims!

Luke.
 
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I'm liking the parts list and the build board. I have some old tandem wheels with heavy gauge spokes from a 70's Columbia twosome that I've been debating on using myself.

Carl.
 
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Looks like a plan Luke! Those tires are going to be B.A. on that bike! I like the black B-17 shaped saddle, more maneuverable off road. Will be fun to watch this come together. Rat on!
 
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Picked up a 6 meter (20 foot) length of 7/8th tubing today and some other steel, I have everything needed to build the frame now, still waiting on one more item before I can build the wheels up though!

Luke.
 
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Well, just got an email that the brown seat I ordered is out of stock, so I will be getting two black ones... That takes one option out of the decision anyway!

Made some really good progress today, it all went pretty much exactly to plan, probably because I had planned the order of the build well in advance while waiting for the metal flake to arrive for 'Pedro'.

Started with two pieces of tubing, one from a Girls 20" fork leg and the other from a weird Boys BMX looking thing, trimmed to size and sleeved ready for welding:

23557506534_b2cb71463f_z.jpg


24103088581_fb109c9b83_z.jpg


Welded, ready for clean up:

24077649482_1fe3ce4da2_z.jpg


Weld cleaned, as you can see the fork drop-out is still attached though, will cut it to length when the frame is ready:

23817885759_cd3536f83c_z.jpg


Tacked into place on the donor Repco MTB frame, all that will remain of the original frame at the end will be the bottom bracket and the down tube, but building it this way I can make sure everything is built straight much easier:

23890081250_de40758eef_z.jpg


Time to add the mid-bar, used some 7/8" tube stock for this:

24103096911_5a1264b0bb_z.jpg


As you can see I decided on a little more seat set back over the original design:

24103098181_88b3658856_z.jpg


All welded:

24103101941_1f48239e03_z.jpg


That was as far as I got on the frame today, next step will be removing the rear triangle off the frame and starting on the new one.

I also worked on the fork today, started out with the top half of an old set of ZOOM suspension forks, decided on these because I think the super sized tubing will suit the bike and I like the crown design:

23817895399_547ab6f7f8_z.jpg


Removed one leg by slicing through it at the weld and chiselling out the remainder:

23557514774_1b4e09cff8_z.jpg


New leg slid in, I had to add a relief cut on the side of the crown as my tubing was 1mm bigger in diameter than the original:

23558920043_8e73dbe102_z.jpg


Took measurements and sightings off the remaining original leg to get the new one dead straight and welded it up:

24159619116_0dc9a21175_z.jpg


Repeated the process on the other side:

24103105751_7c479efbb3_z.jpg


And that is where I got to today, a good start, very happy! I will have to change out the headtube to 1 1/8th to suit the fork, but I think it is worth it!

23890093200_dc3d6a4534_z.jpg


Luke.
 
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Decided to get a pic with the rear tire in place, of course that fat 2.5 wouldn't fit in the original stays so here it is just sitting on it:

23558836264_be5c8f66af_z.jpg


You can see that compared to the original Repco, I have taken about 4" out of the chain stays and raised the rear about 1/2" too for quick turning, should be an awesome ride when it is done! :thumbsup:

Seems like a really small frame but actually it will end up with more reach and a longer seat tube than originally...

Luke.
 
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Wow! Incredible start! Very cool. Love the curved seat tube....so rad! Can't wait to see this one progress.
Thanks Robert! Not my usual style of build, but I caught myself looking at prices on 26-29" BMX's and the other bikes mentioned above, and decided that none of them was really ticking all the boxes for me... Only one answer at that point! ;)

Luke.
 
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Well, just got an email that the brown seat I ordered is out of stock, so I will be getting two black ones... That takes one option out of the decision anyway!

Made some really good progress today, it all went pretty much exactly to plan, probably because I had planned the order of the build well in advance while waiting for the metal flake to arrive for 'Pedro'.

Started with two pieces of tubing, one from a Girls 20" fork leg and the other from a weird Boys BMX looking thing, trimmed to size and sleeved ready for welding:

23557506534_b2cb71463f_z.jpg


24103088581_fb109c9b83_z.jpg


Welded, ready for clean up:

24077649482_1fe3ce4da2_z.jpg


Weld cleaned, as you can see the fork drop-out is still attached though, will cut it to length when the frame is ready:

23817885759_cd3536f83c_z.jpg


Tacked into place on the donor Repco MTB frame, all that will remain of the original frame at the end will be the bottom bracket and the down tube, but building it this way I can make sure everything is built straight much easier:

23890081250_de40758eef_z.jpg


Time to add the mid-bar, used some 7/8" tube stock for this:

24103096911_5a1264b0bb_z.jpg


As you can see I decided on a little more seat set back over the original design:

24103098181_88b3658856_z.jpg


All welded:

24103101941_1f48239e03_z.jpg


That was as far as I got on the frame today, next step will be removing the rear triangle off the frame and starting on the new one.

I also worked on the fork today, started out with the top half of an old set of ZOOM suspension forks, decided on these because I think the super sized tubing will suit the bike and I like the crown design:

23817895399_547ab6f7f8_z.jpg


Removed one leg by slicing through it at the weld and chiselling out the remainder:

23557514774_1b4e09cff8_z.jpg


New leg slid in, I had to add a relief cut on the side of the crown as my tubing was 1mm bigger in diameter than the original:

23558920043_8e73dbe102_z.jpg


Took measurements and sightings off the remaining original leg to get the new one dead straight and welded it up:

24159619116_0dc9a21175_z.jpg


Repeated the process on the other side:

24103105751_7c479efbb3_z.jpg


And that is where I got to today, a good start, very happy! I will have to change out the headtube to 1 1/8th to suit the fork, but I think it is worth it!

23890093200_dc3d6a4534_z.jpg


Luke.
Wow! You are really making progress on the B40! I think you will like your slacker angle on the seat tube, you won't be over the cranks so much with your short wheel base; should make the "downhill" sections more fun. You might want to measure out what that angle is, and then look at modern mtb frame angles for ST and HT to get your new head tube set right so it handles the way you want it to. I like your fork choice! Big and beefy!
 
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Wow! You are really making progress on the B40! I think you will like your slacker angle on the seat tube, you won't be over the cranks so much with your short wheel base; should make the "downhill" sections more fun. I like your fork choice! Big and beefy!
Thanks OJ! Hope I am meeting your expectations!

You might want to measure out what that angle is, and then look at modern mtb frame angles for ST and HT to get your new head tube set right so it handles the way you want it to.
Will do!
Looks like it comes in at 65 degrees, which is pretty much downhill territory, but I want the headtube steeper than a downhill to get the quicker turning...

Nice short wheelbase but long in the frame, probably somewhere around 70-72 degrees?

Any suggestions from you?

Luke.

Edit: Just found out that the Redline Monocog is 71-72 degrees, and also measured the current headtube and my build board, both are at 72 degrees... Is the universe trying to tell me something?
 
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MazdaFlyer

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Loving it Luke!


Sent from my iPhone using Tapatalk
 
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Dig the idea there in the drawing there for the adjustable drops :)
Yep, that was one thing I was set on for this build, best option out there for single speed with disc brakes!
Luke,
Thanks for takin us along with on your build process. Love the welding - wish I was as skilled. :doh:
Glad you are enjoying it! You are wishing you could do what I do, I am wishing I had a tig and the experience to use it! :bigsmile:
Loving it Luke!
Thanks MF!

Luke.
 
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Lookin good Luke, I'm gonna have to use your idea of drawing the bike out for my next build. Gotta make sure I get it right.
Every bike I build from scratch or nearly from scratch I use one now, it saves so much time and worry! Have you seen on my other builds when I draw designs out to scale from drawings? Best way to make sure you get exactly the look you are going for!


Luke.
 

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