KTM 125 XC Rebuild - New Rider, New Upgrades – Our KTM Refresh Story

Reviving the 2023 KTM 125 XC: A Full Refresh for a New Rider

Handing down a dirt bike from one kid to the next is a rite of passage in many families, especially in ours. My younger son, Kase, has been the downstream recipient of many dirt bikes over the years from his big brother Konnor, but I've tried to make them fresh when he gets them. Often, they are better than new/stock when he begins riding them. My 16-year-old son Konnor has spent the last two years putting our 2023 KTM 125 XC through its paces on the moto track and trails, and now it’s time for my 14-year-old to take the reins when the weather warms a bit. But instead of simply passing down a well-worn machine, we’re giving it a full refresh over the winter, so he can start with a bike that looks, feels, and performs as good or better than new.

This project isn’t just about making the bike last longer; it’s about teaching my sons the value of maintenance and taking pride in thier ride. We tore the bike all the way apart and have been meticulously going through each component, ensuring everything is dialed in for peak performance. Here are some ways we’re bringing this machine back to life.

Engine Refresh: Keeping It Running Strong

The heart of any dirt bike is its engine, and after two years of hard riding, it was time for some much-needed attention. The top end received a brand-new piston and rings to restore compression and ensure smooth, reliable power. Even though the KTM 125 XC is a tough and well-engineered bike, keeping up with regular top-end maintenance is crucial for longevity and consistent performance.

While inside the engine, we inspected the cylinder for wear and made sure everything was within spec. The refreshed top end means my younger son will get crisp throttle response and optimal power delivery right out of the gate. The bottom end looked and felt fine, so we didn't make any changes there. 

Suspension Overhaul: Custom-Tuned for the Next Rider

Since my younger son is lighter and has a slightly different riding style than his older brother, and we wanted the bike to perform better than new, we took this opportunity to send the suspension off for a complete update and re-valve. We opted to have MotoXperts in Spanish Fork, Utah, do the heavy lifting.

Here are some notes from Kevin Egbert, who did the suspension for us: "For Kase’s bike, I swapped out the AER cartridges for the current WP Xact Spring cartridges. Very similar to the 6500 cartridges we did on the March Sweepstakes GasGas bike, except that these have a 4mm larger compression piston than the 6500 cartridges (34mm vs. 30mm). It's not necessarily better, but I have a better ability to fine-tune the larger piston. 6500 carts also have external spring preload adjustment, whereas the OEM cartridges do not."

Kevin continues, "the mid-valve piston is also taller and has different port sizes/shapes. The OEM mid-valve has more tuning potential by design than the 6500 mid-valve, which is cool."

He finished telling us, "I revalved the forks and shock for faster Desert/GP style riding & racing, which is still a safe setting for Moto when he doe that. He might find better comfort and stability on the track by going in 2 clicks in (clockwise) on compression and 2-3 clicks in on rebound on the forks, and 1/4-1/2 turn in on the shock HS compression adjuster."

Suspension is one of the most critical aspects of a dirt bike’s handling, and having it dialed in to match the rider’s weight and ability makes a huge difference in control and confidence on the trails. This is the part I'm most excited about and where we spent the most money on this refresh. 

As part of that process, the forks and shock were disassembled, cleaned, and reworked with fresh fluid, new seals, and re-valved internals. This ensures a plush yet controlled ride that suits my 14-year-old’s needs and allows him to progress as a rider.

Drivetrain Upgrades: New Chain and Sprockets

A worn-out chain and sprockets can quickly rob a bike of efficiency and even lead to mechanical issues if left unchecked. To keep everything running smoothly, we installed a brand-new chain and fresh sprockets. I kept the front sproket the same but I decided to add one extra tooth on the rear to drop the gearing just slightly. This will ensure consistent power delivery to the rear wheel, and will be a little easier to ride in single track environments.

We also installed a new chain guide to keep the chain tracking properly, reducing wear on the rear sprocket and improving overall drivetrain durability. Small updates like this help ensure reliability and smooth operation.

Sensor Replacements: Optimizing Performance

Modern fuel-injected two-stroke engines rely on a variety of sensors to optimize fuel and air delivery. After two years of riding, we decided to replace the pressure sensors for ambient air and crankcase pressure to ensure accurate readings and peak performance. These small but important components help the bike maintain its crisp response and fuel efficiency, giving my son the best possible riding experience.

Exhaust and Protection Upgrades

To freshen up the sound and performance of the bike, we swapped out the old silencer for a new one. We opted for the FMF Turbinecore 2.1 since it is also USFS approved with a spark arrestor. A properly functioning silencer helps with power delivery and noise control, and since the old one had seen better days, it was a no-brainer upgrade.

New Contact Points: Grips, Bar Ends, and Controls

A rider’s connection to the bike is key to control and comfort, so we replaced the hand grips and bar ends. Over time, grips wear down and lose their ability to absorb vibration and provide a solid hold. With fresh grips and bar ends, my son will have better control and reduced fatigue on longer rides. The bar ends keep the grips from damage when we do have a tip-over or crash.

Tires: A Fresh Set for Maximum Traction

No bike refresh is complete without new rubber. The old tires were well past their prime, so we will install a fresh set to ensure maximum traction and stability on a variety of terrain. With new tires, my younger son will experience better cornering grip, improved braking, and overall confidence on the bike. There is no better place to spend money than on fresh rubber on your tires.

Aesthetic Overhaul: New Plastics and Graphics

Since we were already diving deep into the rebuild, we decided to make the bike look as fresh as it feels. A brand-new set of plastics and a custom graphics kit give the bike a whole new identity. This not only enhances the bike’s appearance but also makes it feel like a brand-new machine for my younger son, helping him take pride in his ride.

The End Result: A Renewed Ride with a Personal Touch

After going through this entire process, the 2023 KTM 125 XC feels like a completely different bike. It runs strong, looks sharp, and is perfectly tailored to my 14-year-old. More importantly, this project has been a valuable learning experience—showing him how maintenance and proper care extend the life of a dirt bike and improve performance.

Handing down a dirt bike isn’t just about saving money; it’s about building a legacy, teaching responsibility, and keeping the passion for riding alive in the next generation. With this refreshed machine, my son is set up for success, and I can’t wait to see him rip through the trails and the track on a bike that’s been carefully prepared just for him.