Has anyone ever built a bike from scratch?

Thank you! It was fun to build. You get to be my age and tinkering is really satisfying...

Not sure why I never followed up on this but thank you for the mention!  Here is the scratch built YZ250 I did back in 2021: https://www.vitalmx.com/community/MotoRoss678,51018/setup,90784

It was an 06 mainframe, 03 bottom end, and hubs from my 125 when I first started getting the project together.

https://www.vitalmx.com/forums/Bike-Builds,46/Yamaha-YZ-250-Scratch-Build,1388984?page=0

I've built 2 bikes from scratch:

1. 2002 CR250R frame purchased on Ebay, 2001 CR250R bottom end and ignition from a trashed 2001 CR250R I purchased off of Craigslist, and the rest of the bike was assemble using a mix of parts I had lying around, new parts (including the crankshaft and cylinder, and Ebay/Craigslist finds. 
2. 2000 CR250R frame purchased on Ebay, 1993 CR250R bottom end from a thrashed 1993 CR250 I purchased from a friend,  2001 CR250R ignition from Ebay, Ohlins suspension from a KX450 I previously owned, and the rest of the bike was assembled using a mix of parts I had lying around, new parts (including the crankshaft and cylinder), and Ebay/Craigslist finds.

I did a full rebuilt/restoration of a 1974 Husqvarna Mag 250CR decades ago that was pretty ratted out when I got it, because it was my first real hotshot MX bike...and I still think it's the sexiest bike ever. I kept it for quite a while, only riding it occasionally until some financial issues came up & forced me to sell it. Still bums me out to think about it...and I wish I still had pictures.  

Used a period correct toughbook with upgraded internals because what build is complete without aan associated laptop to run the management.  

Your 450 probably has 3 curves and you have to manually switch them, hard, soft, start. This runs 5 simultaneously and they're actuated by TPS position in 20% increments so 0-20% is the first curve, 21-40% is the next, so on, so forth.  Wherever your wrist is on the throttle, is the curve it's using.  The 6 th curve is for sound tech inspection, it goes flat right there where they hold your throttle,  quiets the bike to get it under the dB. 

It also has traction control in the form of rpm threshold tuning (its how you get away with trac ccontrol Without using a Hall sensor).  So, if the TPS position is a constant at say 40% and the rpm climbs, this indicates wheelspin and the ignition curve will flatten to mitigate the wheel spin. 

I can also shut off or turn on the power jet wherever I want using it like a mechanical fuel injector.  This allows you to run a lean, crispy needle, then compensate with extra PJ up high. I have 500 pictures if you want to talk scratch builds.  

Is this a Yamaha 360 with the Öhlins Kit 

Think this bikes are ultra rare , one Shows up on a Marketplace in France the last few Years . 

Ya, Ohlins everything.  The pipe and cylinder are Noleens "best set up" from 1993 when they ran this in the 500 Nationals with Larry Brooks. 

It's a tractor.  There isn't enough crank case volume in 250 cases to support the flow a 360cc twostroke needs.  

Not quite the same as these posts, but in the 1990's there was a UK GP mechanic who was notorious for building bikes out of parts "borrowed" out of the team spares. He'd spend the season slowly building bikes up then he'd sell them at the end of the year. Rob Andrews gives him a mention in his book after being one of his victims 😬

At least when Lee McCollum does it, he waits 20 years. 

Wow great  Bike , i want to hear it 😅

I own some Old KTM 360/380s , this Size are one of the best Twostroke Engines ever made , 500 like power with 250 Handling . 

I have done one bike build starting from scratch back in 2020. I had a 90's ktm 300 engine laying around from a bike I parted out and I wanted to put it in a modern chassis. Pretty much all parts came from Ebay or marketplace piece by piece; bought a 2017 250f frame and then found a great deal on a 2005 250sx engine so ended up going that route. Got a 2015 250 jug from my dad and found that a head from a 2018 would work and made use of the native top engine mounts much easier so it quickly became a Frankenstein engine. I did it as cheaply as I could, I think I ended up around 3k invested to get it rideable. Bike was awesome but I ended up parting it out ironically, wish I still had it. I highly recommend it, hunting for parts is a lot of fun and if you can be patient and wait for good deals it should be fairly cost effective.

Built this 1974 CR 125 from parts found at 3 motorcycle salvage yards around phx az in 1996.

Won the 1997 AHRMA sportsman 125 expert national championship with it.

Still take it out for a ride from time to time.

I came here to say the same thing. Amazing engineering, really pushing the limits of carbon fiber at the time. 
Cancer took John too soon. 
What could have been….