Here’s a small build I’m working on — mostly just trying to revive this YZ125 enough to get it ready for the 125 Dream Race on August 22nd. Time’s tight, so I likely won’t be able to get to everything I’d like before the gate drops, but I’ll get it as cleaned up as I can.
This bike was originally stored in a pool shed, surrounded by chlorine and other harsh chemicals that oxidized nearly every metal surface on it. You’ll see a lot of pitting in the photos — the frame, swingarm, subframe, engine cases, even the carb body all took a hit from the environment.
As for the motor, the top end was scored pretty badly, and the piston had some wear. So we decided to scrap the stock setup for an Athena 144cc big bore kit. That’s the only real performance mod done to the engine besides a pc exhaust that was already on the bike when we got it
Here is what we are working on at the moment.
The suspension was sent off to Hayden Cordell at EVO Suspension to get valved for Sebastian Toth (AMA #329).
I’ve been working on sanding the oxidation and pitting out of the frame, subframe, swingarm, motor, and a bit of the carb body. It’s not perfect, but it’s miles better than where it started.
Installed a KTM radiator fan from one of the off-road models.im waiting on XT60 plugs to show up so i can finish wiring it up to the LiFePO battery we are going to use.
Plastics and graphics are on their way from AMDesigns
Planning to tear down the wheels next and clean up some of the oxidation there.
All bearings look solid, so I’ll just be cleaning and re-greasing them rather than replacing anything.
I'm sure there will be a bit added to this that i will forget to mention but here is some pictures to show where we are at so far.
I will try to keep this post as up to date as i can before dream race, if i cant i will have it updated after dream race! also input/Insight is always welcome! hope to see some of you guys at Washougal
Way to save a worthy scoot 👍
Two notes: Pretty sure those 144 kits can require minor case clearance, so be prepared for that. Also - Make sure your 05' has the updated shift stopper!
https://www.vitalmx.com/forums/Tech-Help-Race-Shop,42/2005-YZ125-Shifting-Problem,1378864
https://www.vitalmx.com/forums/Tech-Help-Race-Shop,42/2005-yz125-won-t-roll-in-gear-w-clutch-in,1386217
https://www.vitalmx.com/forums/Race-Shop,42/05-Yamaha-yz125-shift-stopper,1295044
thank you CRC! yes we ground down the cases to allow clearance for the piston skirt. However I did not know about the shift stopper, I will be ordering one of those ASAP so hopefully it comes in on time.
Just got back to wrenching on this hog after being sick so we’re even further behind than I’d like, but we’ll make it happen!
Got the linkage, swingarm, and triple clamp bearings cleaned and greased. Finished assembling the chassis, mounted the wheels, and then torqued the motor mounts, chassis, swingarm pivot, and linkage under the bike’s own weight. Picked this trick up from an old PC mechanic, it’s supposed to help the chassis stay more compliant since everything has settled into its natural resting spot before you torque it.
Got the airbox cleaned and installed one of the best filters in the game—a WORKZ FILTER (shameless plug). With the airbox and subframe back on, I’m figuring out the wiring for the fan. I ran the switch from the handlebars down the frame spine to meet the wires for the fan, and now I just need to decide where to mount the battery inside the airbox.
im trying to keep vibration to a minimum and to make air filter maintenance easy. Right now, I’ve narrowed it down to two spots, the crossbar mount (my favorite for ease and accessibility, though I need something better than zip ties) or the back left side of the airbox
lots still to get done!
-build a bracket for battery
-Finish wiring
-rebuild front and rear brakes
-new shift stop (if it comes in on time)
-new chemicals (oil, coolant, brake fluid)
-clean up these wheels I hope lol (they are hammered with old dirt and corrosion)
-new tube and tires
-tie wire spokes
-pin the radiator cap
-seat cover
-plastics and graphics
-grip tape
-try and get some more air in the airbox with some holes
-clean up some some areas with some steel wool
I’m trying to knock out most of the functional stuff first, because later this week we’re planning to hit MOTO 541 and spin a few laps. The goal is to get the suspension broke in a little and get the carb settings close enough that dialing it in at Washougal will be easy.
I like your subframe location for the battery much better than the inside of the airbox. Could you fab up some brackets and use the threaded tabs that are on that crossmember?
PS- what's the fan for?
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i think that would end up being the best location too, i will get to work on some brackets!
The fan is mainly for the guy we’re borrowing the bike from. We’ve got a solid mix of technical trails and steep, loamy hill climbs around here, and he definitely takes full advantage, usually at the cost of pistons and coolant. This should help keep that in check. It’s also kind of a version 1 test run before I add one to my own bike, just to make sure it works well. And honestly (probably the real reason) is just because i think it would be bad a$$ lol
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