How to Install a Belt Drive Conversion Kit on a Razor MX650 (Step-by-Step)

Installing a belt drive conversion kit on your Razor MX650 or SX500 takes 30 to 60 minutes the first time. No frame cutting, no welding, no modifications to the bike that can't be undone. Just basic hand tools and this guide.

We'll go through every step, point out the spots where people get it wrong, and make sure you're riding clean when you're done.

Tools you'll need

• Socket set (metric and SAE, 4mm through 17mm covers most fasteners on these bikes)
• Allen/hex key set
• Bike stand or something to prop the rear wheel off the ground
• Clean rags
• Blue threadlocker (for motor mount bolts)

Step 1: Remove the rear wheel

Prop the bike so the rear wheel hangs free. Loosen the rear axle nut (usually 17mm) and work the wheel out of the swingarm. You may need to back out the chain tensioner adjuster bolts first to create enough slack to remove the chain with the wheel.

Set the wheel aside somewhere clean. You'll be coming back to it to install the rear pulley.

Step 2: Remove the old chain, tensioner, and sprockets

pull off the chain, Then unclip or unbolt the stock tensioner and set it aside. You won't be using it, since the stock tensioner isn't compatible with belt drive.

Remove the rear sprocket from the wheel hub. On Razor bikes the sprocket is part of the freewheel assembly, which threads onto the rear hub. You'll need a freewheel removal tool and a strap wrench or chain whip to hold the hub while you break the freewheel loose. Go slowly when breaking it free and confirm it's moving the right direction before applying serious torque.

Remove the front sprocket from the motor shaft. The stock Razor motor uses a 12mm dual D-bore shaft. The sprocket is secured with a nut — a 12mm wrench is what you need. Take note of how the sprocket sits on the shaft before pulling it off so you can reference that orientation when installing the new front pulley.

Step 3: Install the front pulley

The CNC machined front pulley in the MxMods kit mounts to the motor shaft in the same position as the old sprocket. Slide it onto the shaft and secure it with the original reverse-threaded bolt that was used on the chain sprocket. Make sure it's fully seated and properly tightened — a loose front pulley is one of the main causes problems after install.

Apply a small amount of blue threadlocker to the fastener before final tightening. Motor vibration will work it loose over time if you skip this.

Step 4: Install the rear pulley

The rear pulley in the MxMods kit is made in-house from lightweight performance carbon fiber infused plastic and sandwitches the stock rear wheel sprocket. place the side with the logo facing away from the wheel and the other on the opposite and use the 4 included bolts to secure the two halves together

Important: make sure the pulley face is flush with the hub and sitting flat. Any tilt will cause the belt to track to one side and wear unevenly.

Step 5: Reinstall the rear wheel

Slide the rear wheel back into the swingarm. Don't fully tighten the axle yet. You want the wheel to have some adjustment room when you route the belt and set tension in the next step.

Make sure the wheel is centered in the swingarm before you start. Uneven wheel position will cause the belt to run at an angle and dramatically shorten its life.

Step 6: Route and fit the belt

Loop the belt over the front pulley and rear pulley. You'll need to work the wheel toward the motor to get the belt over both pulleys with enough slack to seat it in the teeth. This is easier with two sets of hands but doable solo.

Once the belt is seated on both pulleys, check that it's sitting evenly across the full width of both. The belt should be centered on the pulley face with the same amount of clearance on each side. If it's riding to one side, the pulleys aren't aligned and you need to correct this before tensioning.

Step 7: Set belt tension

This is the most important step of the whole install. Belt tension determines how long the belt lasts and how well it performs. a belt tensioner is necessary for the kit to function properly. you can buy ones from our shop

If you're using the MxMods motor tensioner, it mounts to the stock motor bracket and gives you a single adjustment bolt to dial in tension. Tighten it until you get the right deflection and lock it in place tightly.

Target tension: Press on the middle of the belt's longest free span with your finger. It should have a small amount of give but feel firm, not floppy. If it pushes easily with almost no resistance, it's too loose. If it barely moves at all, it's too tight. if you hear a grinding noise when applying power, it means your belt is too loose and it needs to be tensioned more.

Apply blue threadlocker to the motor mount bolts if you haven't already. These will work loose over time otherwise.

Step 8: Tighten the rear axle and do a final check

Once tension is set, slide the rear wheel into its final centered position and tighten the axle nut to spec. Spin the rear wheel by hand and watch the belt track. It should run centered and straight on both pulleys through the full rotation. If it walks to one side, something isn't aligned and you need to find it before riding.

Do a quick check of all fasteners: motor mount bolts, front pulley bolt, rear pulley, axle nut. Everything should be tight.

Step 9: First ride and fine-tune

Your first ride with a new belt drive should be short, 15 to 20 minutes, and relatively easy. This lets the belt seat into the pulley teeth and settle into its running position, as well as pre stretch the belt.

After that first ride, stop and re-check belt tension. Belts commonly relax slightly in the first few miles and will often need a small tension adjustment. This is normal, not a sign of a problem. Re-check again after the first 5 hours of riding, and then monthly after that.

Common installation mistakes

• Cross-threading the front pulley. Always thread it on by hand first and make sure it's turning smoothly before applying any real force.
• Skipping the freewheel weld. On a high-torque build, this will eventually cause the freewheel to back off under load and lose engagement. Weld it.
• Using the stock tensioner. It won't work for belt tension. You either need the motor tensioner or careful shim positioning.
• Not checking pulley alignment. A belt that's running at an angle will wear through in a fraction of the normal lifespan. Check alignment before you ride.
• Over-tensioning. More tension is not better. A belt that's too tight loads the motor bearings hard and will wear them out faster than a chain ever would.
• Skipping the break-in ride. The belt needs a chance to settle. A hard first ride can cause it to skip teeth before it's fully seated.

Troubleshooting a fresh install

Belt skipping teeth: Almost always too loose. Re-check tension and tighten slightly. Also verify the front pulley is fully seated and tightened on the motor shaft.

Belt walking to one side: Pulley alignment issue. Rear pulley is probably tilted or the wheel isn't centered in the swingarm. Back up and fix alignment before continuing.

Loud clicking or rattling sound: Check for debris caught between the belt and a pulley. Also check that the belt is seated fully in the teeth and not riding up on the pulley flange.

Rear wheel hard to spin by hand: Belt is too tight. Back off tension and re-check.

Motor making more noise than usual: Could be over-tension loading the motor bearings. Back off belt tension slightly and see if it improves.

Once you're done, check out our full belt drive guide for tensioning and maintenance tips that'll keep the system running at its best long-term.