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After picking this up and seeing some crispy wiring, I decided to send the electronics back to Oset for diagnosis and embark on a little restoration effort to get this little trials bike ready for my son’s birthday in July.
As she was on pickup.
Batteries out.
Melted main fuse was early sign of trouble.
Throttle, controller and wiring stripped. The motor sits between the swingarm halves and took a bit more effort to remove.
Motor out and spun well with 12V applied. Got all the electrics boxed up to send back to Oset. They’d offered to troubleshoot *for free.*
Ready to take apart the chassis, forks are toast (play between lower and slider, bushings are done).
Will go over the findings and replacement parts ordered in the next post.
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Looking forward to following, thanks for taking the time to take pics and post, love a good build thread.
Some of the stuff I found confused the Oset guys, in the earlier days builds were pretty iterative and I’ve had to send pics of some specific issues so I’ve got some good documentation. Took videos of wire routings prior to disassembly so I’m hopeful of a positive process!
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Findings from Oset were as follows:
Bad: Battery wiring harness, potentiometer / speed control, relay and motor controller.
Good: throttle, key switch, charge port, and the biggie, the motor.
I discovered play in the front end that I thought was the steering bearings, but it’s the fork slider bushings that are smoked; and the real wheel bearings were done.
New wiring, motor controller, etc from above, plus a fork, steering head bearing kit, chain, brake pads, and wheel set (with bearings, tires and tubes mounted) ordered and received from Oset, who included some additional schematics and wiring diagrams for me. Solid folks there!
Instead of new lead acid batteries I opted for a LiFePo4 upgrade to two, 12v 18ah batteries that should weigh a fair bit less and provide for longer run time and more stable storage. Batteries are warrantied for 11-years.
Got the old parts through the parts washer and ready to think about reassembly.
Bearing races out:
Also had to touch up a couple of chips on the new forks, but they’re ready to go as well.
Hope to put things together this weekend with my son if all goes well…
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Oh f yeah![]()
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1994 Yamaha YZ250 CA Street Legal 2-smoke :smoke:
Can't believe how helpful Oset have been!
They’ve been super helpful!
Wee problem with the new fork. It doesn’t have an upper triple clamp like the old one does, it’s more like a bicycle fork with all the triples and sliders located below the lower triple clamp. Issue being, the top triple acts as a spacer which without it, the remaining spacers leave too much of the steering stem showing at the top.
Here is the old top triple mounted with old spacers and the height at the top is perfect for the top cap and screw that goes to a star nut in the steering stem.
Here is the stack height without the triple and not in the correct order to illustrate the amount of steering stem showing.
I’ll bring the triple and spacers over to Ken to fab up a new solution. I’m the meantime leaving the TC in so we can keep going.
I put the swingarm halves together with the motor inside.
My son helped swap brake discs, sprocket, and get the wheels mounted up, so we’ve got a roller and the suspension action is nice with him on it!
That might be it for now, gonna get the top triple and spacers off again, and then it’s time to mount the electrical stuff.
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awesome project ! we loved our Oset 12.5R. great bikes.
Beta 200RR
The brake looks like it is a bicycle brake as well. Looks like one that I just replaced a month or so ago on one of our loaner bikes.
https://a.co/d/3xuLxOT
-Christian LRRS/CCS HasBeen ECK Racing
2011 Pit Bike Race CHAMPION!
spacer looks great but curious why you didn't just cut the steerer tube, bars too low?
Beta 200RR
This preserves stock height and the fork had an internal star nut preinstalled… not sure if I could’ve gotten it moved further down the stem but either way I never considered cutting the stem. As was seemed to fit my son well so yeah, didn’t want a lower bar which would make it a little harder to stand whilst riding.
Oset makes some spacers, but I prefer this to a stack of spacers. Came out exactly as hoped for!
The new front doesn’t look quite as “motorcycle” as the old fork with longer tubes, but it’s waaaay lighter and actually has some nice damping to it vs what feels like an internal spring only in the original fork. Should be a nice upgrade in use.
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Just a short while in the garage with my son before supper, got the brakes mounted up and adjusted.
One of the adjusters at the levers was totally mung’d up.
New ones sourced on Amazon.
Not bad..
All set for today.
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I'm loving this thread. Thank you. It's getting me so amped for when my boy can start riding bikes.
-Alex
I can resist everything but Pete's mom.
Back on topic, since it’s a washout today Cal had time to help get some of the electrics on the bike.
First up was to get the hard mounted small components on the bike. Ignition, potentiometer (speed control) and charge port (altho I won’t be needing this with the new batteries).
Here’s how they should orient, all facing to the rear of the bike (mounting location is a cross bar between the frame rails forward from the shock mount).
Reviewing an old video I took pre-year down, I got confused as the charge port was mounted backwards.
Here is the back side (forward facing on the bike) part where all the wiring comes out below the relay and up to a common location.
View looking down from top.
Controller sits behind the steering head.
Motor wiring and connector tied to the frame. They seal the back of the connectors with epoxy.
Now we’re waiting on the batteries. Balancing them by fully charging each individually with a 12V charger. After which I have a 24V charger but need to integrate it with the charge port wiring.
Kid got bored just before the cable tying, but otherwise helped with quite a bit! Learned how to use a Vice to straighten a twisted key, and helped get the hard mounted stuff attached to the bike, and learned what the acronym RTFM means with respect to the erroneous charge port orientation… we checked the owners manual and confirmed based on their images.
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*eye twitches
Whoa, I thought it was a full size trials bike, lol
I was way off!
Haha no, this is the second smallest bike Oset makes. The 12.0/12.5 is basically like a strider bike equivalent for little kids. The 16.0 is for 5-7 year olds and has a max weight of 135 lbs or so. The 20 is for 8+, but only the 24 is rated for 198 lbs… altho the Oset guys say 250+ have ridden the 20 and 24s.
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