Turning an Old Hardtail into a Custom Dirt Jump Bike

May 24, 2020
by Nick Dunn  
The completed DJ from an old hardtail

I have always wanted to build my own bike frame, but I have never had the right opportunity to do so. I never had the chance to work with metal as a kid and certainly didn’t think that I had the skill to build my own frame. This is where my high school senior project came in. I knew from my freshman year that I was going to weld my own frame; somehow. Three years passed and this is what I did.

The first obstacle that I came across came pretty quickly. I knew that just building a frame would be super sweet; however, my project had to have more significance to it. This is where the idea of changing the geometry on an already built bike came in. I wanted to keep at least one bike from ending up in the dump so I purchased an old Diamondback hardtail from Facebook Marketplace for $25, and the journey started.

This bike was headed for the dump until I came in.


The Process

I learned how to TIG weld with a local Welder and machinist, Mike Barklow https://www.instagram.com/metalmindset/. I would go to his shop after school and practice welding, moving to thinner and thinner material each time. Overall, I spent one day, 24 hours total, learning how to TIG weld. This was a very critical part of the project, as I had never welded before this. I learned a bunch! Each week we would work on a new technique, or move to a new piece of metal.

Mock Headtube coat rack
Mock head tube that I made while practicing


Back to the bike. I stripped the $25 bike of parts and paint and began cutting the frame apart.

Stripping and getting ready to cut frame


This process of cutting the frame apart was easy, yet nerve-wracking because I didn’t want to mess up on the first step of the build. I decided to keep the rear end together to help cut down on the welding that I would need to perform. This ended up being a huge time saver and adds a bit more character to the bike.

Making the cuts

Rear end mocked up


Now onto the actual frame building. I was fortunate enough to have the help of the very skilled, Wes Van (https://www.instagram.com/wildflowerbicycles/), during the frame building portion. We designed a frame in BikeCad that would work for the already small tube lengths, a dirt jumper. We then started building. The rear end was easy. we bent the seat stays down to match the cut seat tube. We ended up brazing the junction of the seat stays and the seat tube because of how difficult it would have been to miter the stays since they were still connected to the rear triangle. This was my first time brazing, and it was pretty fun. I know that my brazing is not perfect, but that is the theme of the bike.

Brazing the rear triangle together.

Pretty shabby, but not too shabby for the first time Brazing.

Once the rear end was done, we mitered the top tube and down tube. I used the original downtube as the top tube on the dirt jumper. Wes had a dented downtube that I used, and I bought a new head tube. Mitering was super easy thanks to the tooling that Wes has.

Mitering and the frame in the jig.

Once mitered, I tacked all the tubes in place and started welding. As expected, I blew a lot of holes in the frame (whoopsies), but that is just the process of welding thin material. I patched some of the smaller holes, and Wes came through as the cleanup crew and patched some of the bigger holes that I made.

Halfway done welding!

Putting on the brake tab seemed easy enough, but because we didn’t have a jig for quick release dropouts, the position is a bit off. For now, I am just running brakeless, which is super fun but scary at first. We finished up by reaming the head tube and calling it good. I put a clear coat on the frame to show off the sub-par welds and the franken-bike feel.

Newborn franken-frame, fresh off the welding table

I built up the bike using a mix of parts from the original bike, parts I had at home, parts from Cycle-Z (a bike repair club at my school), and some new parts. I tried to keep the recycled theme throughout the bike while building it up.

From this, to this

Overall, I spent 49 hours and around $250 total to transform this dump destined bike into a snappy jump bike. Although keeping only one bike out of the dump is not super impactful, I think that this project shows that it is very possible to repurpose old frames that many people find no value in.



Huge thanks to Mike and Wes for their tremendous help in completing this project! This project wouldn't have gone anywhere without their help and generosity! Check them out on Instagram https://www.instagram.com/metalmindset/ and https://www.instagram.com/wildflowerbicycles/.








49 Comments

  • 54 0
 Nice work. So much pleasure in using something you made yourself.
  • 29 0
 Right on for being creative! Cool idea to recycle an old beater.
  • 2 0
 Seriously! What a great idea. The beauty is you can keep perfecting the learning curve because there is so many bikes like that out there to cut apart and use.
  • 14 0
 As a high school teacher I want to say a job well done. Way to have a goal, run with an idea, balance time with school, look for resources, utilize local professionals willing to help, and give credit where credit is due. You are way ahead of the curve with ambition and drive compared to many your age. Keep it up.
  • 6 0
 I’d chop the rear dropouts off and make some horizontals. Too be honest though 4130 is so cheap it’s more time/cost effective to start with a pile of new tubes. I’ve done it. The same as this kid when I was a kid but I used a Mig welder, surprisingly it never broke then later from scratch and tigged.
Good work though hombre
  • 1 0
 Idea is to recycle though...
  • 1 0
 @pgins: just give your old shitta to the Salvation Army
  • 1 0
 @pgins: I was half joking with that.
But seriously if the kid wants to build bikes I was trying to give him good advice. I wouldn’t feel totally happy about a child of mine sending big jumps on a bike that started out as a 1990’s xc racer.
  • 10 0
 very cool
  • 6 1
 Seems like there has been an uptick in DIY projects featured on PB lately. Much appreciated. Great to see someone start out clueless, but decides to go for it anyway, and actually pulls if off. Mr Dunn will be welding Ti next.
  • 3 0
 Absolutely. Great to see content like this. It's inspiring.
  • 6 0
 Bet you feel a lot prouder blasting round in this than one you would have bought
  • 6 0
 I thought you were wearing old Oakley Factory Pilots as welding goggles. Freaked me out .
  • 2 0
 This is awesome. I did something similar many years ago (and by "I, " I mean my friend who knew how to weld did most of the work). But yeah, we re-used most of an old univega. Only downside was that the chainstays were kinda long for a dirt jumper.
  • 2 0
 An old buddy of mine, his co-worker fixed an old Breezer Lightning frame that cracked. It cracked almost all the way around the BB shell where it meets the seat tube and part of the down tube. he arc welded the area back together, welds now look like something you'd see on a GT (fugly but strong). Since then, several years later, the area he fixed is still fine but, now I think I see cracks starting to form around the headtube, top tube and bottom tube intersections -- very small but, l'm pretty sure those are cracks I'm seeing under the paint. I'm just going to retire this classic MTB and some day, I'll mount it to the wall with LED light strips on the back side for a little wall art / lamp combo. The light strips along the frame will illuminate the wall. Should be pretty dope when I'm done.
  • 37 36
 Yeah, $250 sounds like a wicked number, but how many of us have access to a tig welder, frame jig and hours upon hours of practice with a professional welder (which most are very much, not pro-bono) this ends up looking a lot more than 250.

But still fcking cool.
  • 5 0
 TIG welder are cheap those days, frame jig can be made with cheap pieces of wood and an OSB plate.

And Youtube videos are your master those days.

But he is using brazing here (acethylene+oxygen bottles), I bought the kit, still need the gas bottles.
  • 3 0
 Cry baby
  • 3 0
 Yeah!!! i've done the same thing with a old brolen Marin bear vallye but no to make a dirt but a gravel bike.. But, i'hadn't Anvill Jig!!! Smile
  • 3 0
 What about a gusset on the headtube-downtube junction? Wouldn't it make the frame stronger?
  • 4 0
 More articles like this please.
  • 2 0
 Awesome dude! I was learning to weld when I was at high school. I did about an hour. Should have done the extra 23!
  • 4 5
 Looks like most of the frame was TIG brazed. On the next one wash the toes of the welds more into the base metal and try to fill any voids to prevent cracking. Looks like it is old 4130 tubing. 1/16" filler wire in 4130 should do the trick. Not sure of 309L SS would work in this application. Also I think there is a bit of a pre and post heat procedure to keep things straight. Looks like a fun rig.
  • 3 2
 Lots of words that I have no idea what they mean... I think they call it tire kicking
  • 2 0
 Jolly well done!!! Care to share some more info on the bike's geometry as it is?
  • 1 0
 Thought about doing something similar. I would cut the stays , down tube , top top to shorter length and then glue back together with carbon fiber.
  • 2 0
 The best way to learn, by doing - would love to do something like this if I had the time!
  • 3 0
 That's awseome kid!
  • 2 0
 That is super-sweet, idea and execution! Props!
: )
  • 2 0
 Well played. I love the rainbow look of raw welds.
  • 2 0
 Sick! Always wanted to do thisq
  • 2 0
 Thats rad, not sure I would trust riding a bike with my own welding
  • 1 0
 So cool. Respect your curiosity and initiative. Have fun riding it and keep experimenting!
  • 1 0
 That's dope. Great job. Never imagined that would be done.
  • 1 0
 Looks friggen sweet dude!! Jealous!!
  • 2 1
 Be cooler to see some riding on it - needs a riding vid!
  • 1 1
 Get a proper sprung tensioner and a chain stay protector. Keeps the slap to a min.
  • 1 0
 nice, you make your dream bike. good job dans skills .
  • 1 0
 You had a couple of parts welded for a high price. Cool, I guess.
  • 1 0
 Nice work man!
  • 1 0
 Great job
  • 1 0
 Great job mate!
  • 1 0
 Solid work nick!
  • 1 0
 so rad. good work!
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