How I Built A YZ250F With A Box of Scraps

What do you get with a bin full of dirt bike parts and an eager mechanic looking for excitement and satisfaction? A great project rebuild! If you are a dirt bike grease monkey like me who not only likes riding their bikes but sometimes working on them too then this is for you. I enjoy project rebuilds and love the oh-so greatly anticipated finished product even more. Ever since I got into dirt biking I have gained more knowledge about how they work and how they are put together. So after doing many rebuilds myself I thought that I would share the experience with you fellow riders.


I bought this 2003 Yamaha YZ250F in pieces as a project bike thinking that I would have some fun and get some more experience putting another bike together over the next month after I bought it. It came needing a complete new top-end at the least. I managed to get one and put the engine together in a reasonable amount of time. I then slapped the engine in the frame and started the process of puzzling the rest of the bike back together; this is where the fun started. It only took a few short minutes of bolting parts on to find that there was stuff missing. The more I put together the more parts I found that were missing or broken, and they were not all at the same time. So one-by-one I had to buy parts that I needed to piece this thing back to its somewhat original form. These parts consisted of, including engine parts, clutch plates, radiator shrouds, timing chain, timing chain slider, a different piston, head pipe, a couple crank bearings, engine/frame mounts, air filter, cylinder head breather hose, chain, gas tank, clutch perch assembly, a shift lever, and maybe a couple other miscellaneous things. Figuring out that we had to find and buy these parts got a little frustrating because we were told that the bike was complete and that it just needed a new top end.

Well, after weeks of picking at my wallet this bike has finally been put together and is running. It just needs a couple things put on to be ride able. So once I get those together I’ll take it out for a spin. The process was long and somewhat miserable, but I think I learned a lesson and gained more experience and knowledge about these modern four strokes that basically took over the world. In the spring, if not sooner, I will be putting on some new bling to make this baby look new, but as of right now it’s a clean bike that runs. Thanks for checking out this rebuild process, and make sure to check back in the near future for another bike rebuild! (If you liked this article make sure to check out my other rebuild, “I Rebuilt My YZ125 In A Closet!?

-Tom Stark

P.S. I might update this article with some pictures and/or video once I get this bike looking good. Questions and comments are welcome.

When I got the bike (as you can see, I had my work cut out for me):



Pic of the damaged cylinder head:


After I cleaned it up and the engine was together in the bike:


Put the wheel and handlebars on:



The bike put together (added sub frame, carb, electronics, old plastics, seat, exhaust, cables, etc.):


The finished product…


Renewing the ’01 YZ125

So I decided that I wanted to give my dirt bike a good look before I sell it. It originally was my first race bike, but I have bought a newer one, so I will not be needing this anymore. It has been a great bike and very reliable to me. The bike is also very fast. I try to keep my bikes clean and well maintained so that when I sell them it looks nice and I can sell with confidence. My bike did not look the greatest when I first got it, but that’s because it didn’t have any plastic on it. For racing I just put some used plastic on so that I could at least race. Although I am a racer and a younger person, I did not beat the snot out of it and trash it like most people do. I did ride it somewhat fast at times, but I always kept it running and looking pretty clean. Now it is time to sell, so I have brought back the stock look of the bike with the addition of New Plastics and graphics. I have always liked the look of stock bikes better than most aftermarket graphics. I will miss this bike a little, but there’s many more fast bikes to come. Thanks for reading, and stayed tuned for more posts soon!

-Tom Stark

When I Got The Bike
Bike With Some Used Plastics On
Bike With Matching Tank
Bike Refreshed With Cleaning, New Fenders, and Graphics

1996 KX250 Rebuild A Junkyard Wildabeast


In this rebuild project a 1996 KX250 was bought for $200, the only parts that appeared to be missing were the silencer, some plastic body components, and  the front brake reservoir. 1996 KX250


As I began the tear-down i began realizing just like Tom in many of his rebuilds, that many of the parts were discreetly missing. I first noticed that the Carburetor slide was missing after I took off the sub frame, air box, and carburetor. I had already known that the bike needed a new crank, crank bearings, and a top-end; and there was no telling about how bad the motor damage would truly be knowing that the bike sat outside in the rain, sleet, and hail throughout winter. 1996 KX250Of course I knew I was going to have to strip all of the bike down to the frame and replace and grease every bearing and moving part, especially the swing-arm and shock bearings.

Unexpected Problems

After I began the dis-assembly and long restoration process for the bike I en-countered a major problem, the swing-arm was severely busted up and every bolt you could think on the entire rear end of the bike was stripped, rounded, or cross-threaded. So I then began the process of looking on eBay for a swing-arm in decent shape.

I observed the characteristics of the 1996 swing-arm and discovered that the 1994-1998 model KX125s and KX250s were very similar,  so I ordered a very nice or at least decent shape 1998 KX125 swing-arm. Along with just being in better shape, the 1998 swing-arm offers better handling than the 1996 swing-arm. The 1996 swing-arm is about is about one inch shorter and about one inch less in width. Another advantage of using the 1998 swing-arm is that it is made out of aluminum so it is lighter, and the longer length provides better cornering and less front wheel pop in the straights.

Frame Repair

The frame was badly rusted and the sub-frame needed a new mount re-welded. First, for the main frame assembly I treated the rust and primed the frame. The main frame was then painted “alloy silver”.

Motor Tear down

The top end only took about 5-minutes to tear down, I could tell I was definitely going to need a cylinder sleeve and piston. Once the top end was disassembled I removed the clutch cover and removed the clutch plates, clutch springs, clutch inner and outer basket, and clutch actuator rod. Next, the kick starter assembly was removed and the water pump was removed, good thing the water pump was removed because the impeller was  froze. For the final dis-assembly part, which was splitting the cases, I used a Tusk Crank Case Splitter from This made taking out the crank and transmission easy. Here are some pictures of the dis-assembly…

Motor Assembly

The cylinder needed a new sleeve or to be chromed by a shop such as U.S. Chrome. I realized that for slightly $30 more I could buy a very nice cylinder off of eBay with a new cylinder sleeve, a slightly used piston, a KIPS cover, and carbon fiber reeds; All of which I was going to buy anyways. With all the new tools I bought I was slightly out of my budget, which was why the project got put on hold for several weeks, thanks to finding great buys on eBay I was able to jump right back on track with this project!

First off, since the motor was already disassembled there was no delay to install parts. I installed some new All Balls Racing crank bearings, although All Balls Racing products are cheaper they are not cheaply made, and they have been proven in amateur racing. Next, the crank was installed using a Tusk Crank Case Installer tool, due to the way the threads are on the crank of older KX250’s I had to buy a dye to use the tool. You may think why doesn’t he just use a mallet? But the answer is simple enough, if I was to use a mallet the Crank would no longer be balanced due to beating on the crank with the mallet. After the crank bearings and Crank were installed the transmission was installed. The bottom end of the motor also received some new shifter forks due to the severe beating it took from the last owner. Next, the crank cases were put together using the Tusk Racing Crank Installer again. Finally, the top-end was installed along with a new Athena gasket kit.

More Unexpected Problems

As I began to disassemble the rear wheel I realized that the rear hub was cracked, It’s hard to believe how mistreated a bike can be, especially when you take into consideration that it was once a brand new bike of a proud owner.Due to the hub being cracked I decided to go ahead and buy some nice aftermarket wheels. I decided to go with RAD MFG. Econo Wheels because they offer a great price for the package and the only issues i’ve heard of them have been about the wheel spacers. Not to mention the offer a trick look, thanks to RAD MFG.’s in-house anodizing, so i went with a Lime colored hub and a Black rim with Silver spokes and nipples.

Trying to Finish the Project

I had a very nice 2004 KX125 loaded with ProCircuit goodies, but unfortunately I had to be willing to sacrifice one my bikes to finish the rebuild. So after about a one month break from the project, and  after selling my 04′ I decided I mind as well dump some more money into this bike and just keep it. Since I now had $2100 in my pocket I decided to get the rear shock spring, frame, and swingarm powdercoated matte black. I also had to buy some forks along the way since mine were corroded. I bought 3 sets of forks of ebay, all of which were damaged just as bad as mine. So I finally decided to start browsing on Craigslist, and I finally found a set of 96′ kx250 forks two days later. Come to find out I also had to spend $35 on some tripple clamps because I later figured out I had a 96′ frame and motor with 95′ forks, which are 2mm.s smaller in fork tube diameter. So after  I figured all of that out I began assembling the frame, I’ve also been waiting for some parts so I decided to make some brackets and trim so older plastics so I could use the newer style (03-05) style plastics. Here are some pictures…

Rad Mfg. Wheel

Powdercoated Parts

Assembly and Plastic Conversion

Just When I Thought I Was Almost Done Buying Parts!!!

My new plastics finally arrived, so I began making the adjustments to make them fit. I also ordered OEM levers, swingarm hardware for the chain slider, and new pistons for the front brake caliper. All of which was around $140. Later on I ordered some black side panels, which I found out are very hard to find for this year and model, and some wave disc rotors for front and rear. I also bought a new rear Dunlop tire from  a local dirtbike shop. I was about to install the motor but I found a very small crack on the connecting rod, so now I must also buy a connecting rod or complete crank. It’s kinda bad, yet good at the same time that I found the crack because it probably would have messed up my cylinder wall plating and new piston. Although it seems i’m back to square one I’m really not. Now that I have to save up some more money, since my parents put  $1900 of my money savings Arrrgggghhhh!!! I mind as well spend about $35 at local shop to get the cylinder (The plating was beginning to wear away.) bored out 1 mm. so I will know that the bike will be race ready and run good for years to come, along with buying a new crank assembly so the crank doesn’t need to be balanced after the new connecting rod is installed. Here’s some more pics…

The Final Assembly… (yep, the third complete assembly of the bike!)

After I recieved the parts I began re-assembling the motor. I installed a new crank-shaft assembly and Wiseco piston I also replaced the water pump impeller. After I assembled the motor I installed the rest of the electrical system and put the motor in the bike. Everything on the new subframe lined up perfectly, although at first I didn’t think it did because the UFO side panels didn’t fit. The rest of the bike went together fairly smooth except I spent several months ordering the rest of the ‘odds-and-ends’ when ever I had the money…  Below are the final pictures of the bike and further down on the page is a complete parts list with the total cost. The only thing the bike is still lacking are some nice graphics…

I made the pictures big so all the details are easier to see…

All Done!!!!

Parts List

Used Parts

  • New airbox
  • Cylinder (replated)
  • Swingarm
  • Carburetor
  • Forks (newer and larger diameter)
  • Radiators (sprayed with paint remover to remove stock black paint)
  • 98′ electrical system with TPS sensor for carburetor

New Parts

  • 94′-98′ style rear fender, side number plates, and radiator shrouds made by UFO plastics
  • 03′-07′ style front fender and front number plate
  • Renthal handlebars
  • ProTaper pillow top grips
  • Anodized works connection brake covers and assorted hardware
  • Factory Effex seat cover
  • FMF Gnarly
  • FMF Powercore II
  • ProCircuit Linkage
  • UFO gas cap
  • Motohose colored hose kit
  • Tusk racing Chain
  • JT rear steel sprocket
  • JT front steel sprocket
  • Renthal Brake pads front and rear
  • Galfer brake lines
  • Cyrca Handguards
  • Off brand wide footpegs
  • Turner performance chaing guard and roller wheel (red)
  • Tusk Racing Wave rotors front and Rear
  • Acerbis chain slid plate (rubber)
  • Topar Racing billet clutch cover and case saver
  • MotionPro clutch and throttle cables
  • Wiseco piston and Crankshaft assembly
  • Koyo crank bearing and water pump impeller bearings
  • Rad MFG. Econo series Hubs (green)
  • Rad MFG. Rims (black)
  • Heavy duty spokes
  • Heavy duty tire tubes
  • Aluminum rim locks
  • Dunlop tires front and rear
  • And approximately $450 in specialized OEM hardware (bolts)

And the running total is… $4,327.73

I’m very sorry for the long delay in updates and slow progress, but unfortunately I ran into some family and money problems along the way. I also had to stop spending money on the bike for about 3 months because I had to purchase my own truck when my father bought my step-sister a BRAND new Volkswagen Jetta. Although my problems aren’t your problems I just felt as though I should explain why the build took such a long time ….

As of 11/2/2013 the bike is still running strong and is 100% completed now!