Razor MX650 Chain Problems: Every Fault, Fix, and Prevention Trick

The Razor MX650 is a genuinely good little electric dirt bike. however the chain can create major problems.

Chain problems are probably the number one complaint in the Razor modding community, and for good reason. The stock drivetrain was built for a light, slow, stock bike on flat ground. Once you push it harder than that, the chain starts to struggle. This guide covers every common chain problem we see on the MX650 and SX500, what's actually causing each one, and how to fix it. And for a few of them, we'll be honest that the best long-term fix is getting rid of the chain entirely.

Why Razor MX650 chains cause so much trouble

Before we get into the specific problems, it helps to understand why they happen in the first place.

The stock Razor MX650 chain system was engineered for a 36V bike doing 17 mph on relatively flat terrain. That's the use case it was built for. In practice, most riders push it harder than that, whether through aggressive riding, heavier loads, rough terrain, or motor upgrades. The chain itself isn't necessarily a bad chain for what it was designed to do. It's just constantly being asked to do more than that.

Add to that the fact that the stock tensioner is spring-loaded and fairly simple, the motor bracket has some flex in it, and the frame takes a beating on rough ground, and you've got a recipe for a drivetrain that needs constant attention. That's not a design flaw so much as it is a mismatch between what the bike can do and what the stock chain system was built to handle.

Chain slipping under load

This one usually shows up as the bike losing power suddenly under acceleration, then recovering when you back off the throttle. It feels like wheel spin, but the rear tire isn't actually slipping on the ground.

What's causing it: Either the chain has stretched enough that there's too much slack, the sprocket teeth are worn down enough that the chain isn't seating properly, or both. A worn chain and worn sprocket will skip teeth under any real load, especially from a stop.

How to fix it: Start by checking chain tension. Press on the chain at the midpoint between the sprockets. There should be a small amount of play but not so much that the chain feels floppy or droopy. If there's significant slack, the chain has stretched and needs to be replaced or adjusted if there's still room in the tensioner. Next, look at the sprocket teeth. If they're pointed or hooked rather than flat-topped, the sprocket is worn and needs replacing along with the chain.

Replacing one without the other is a common mistake. A new chain on worn sprocket teeth, or a new sprocket with a stretched chain, will wear out faster than if you'd replaced both at the same time.

Chain falling off

This is usually a tensioner problem. The stock Razor tensioner does its job, but it's spring-loaded and not particularly rigid. When the motor bracket flexes under load, or when the bike lands hard off a jump, the tensioner can lose its position and let the chain go slack just long enough to derail.

What's causing it: Tensioner misalignment, a weak or worn tensioner spring, or a motor mount that's shifted position. If the chain keeps coming off the front sprocket specifically, check that the motor hasn't moved in its bracket.

How to fix it: First, re-seat the chain and check the tensioner position. If the tensioner looks fine but the chain keeps coming off, check the motor mount bolts. They work loose over time, especially on rough terrain, and even a small amount of motor movement can throw the chain alignment off enough to cause derailment.

If this keeps happening after you've tightened everything down, consider upgrading to a solid adjustable tensioner. Our motor tensioner is cut from 3.2mm cold-rolled steel, which means it doesn't flex or shift the way the stock setup can.

Chain skipping or jumping teeth

Chain skip is different from chain slip. Skip has a very distinct feel, like a sudden jerk or clunk, usually under hard acceleration. It's the chain jumping over a sprocket tooth rather than riding smoothly across the face.

What's causing it: Usually worn sprocket teeth, a stretched chain, or a combination of both. In some cases it's a chain that's just too loose. It can also be caused by a bent link in the chain.

How to fix it: Run through the chain with your hands and feel for any stiff or bent links. Replace the chain if you find any. Check sprocket wear. If the teeth look pointed or asymmetrical, replace the sprocket. If both the chain and sprocket look fine and you're still getting skip, check alignment between the front and rear sprocket. They need to be in the same plane or the chain will always want to ride off-center and skip.

Chain making a grinding or scraping noise

A chain that grinds or scrapes is usually rubbing on something it shouldn't be. Most commonly the chain guard, the frame, or a misaligned sprocket.

What's causing it: Misalignment is the most common cause. If the rear wheel isn't perfectly centered in the swingarm, the chain runs at an angle and rubs against the edges of the sprocket or chain guide. A chain that's too tight will also press harder against the guide and make more noise.

How to fix it: Check rear wheel alignment. Most Razor swingarms have adjustment points on both sides, and they need to be set symmetrically. Back the wheel out, verify both sides have washers, and re-seat. Also check chain tension and back it off slightly if it feels like it's under a lot of tension at full extension of the suspension.

Chain breaking

A snapped chain is the most dramatic failure, and usually the most predictable one in hindsight. It almost always happens after a period of smaller warning signs that got ignored.

What's causing it: Usually the chain was already worn or stretched, a link was already weak, and then a hard acceleration event or an upgrade put enough force through it to finish the job. Modded bikes are especially prone to this because the motor can put out torque spikes that the stock chain simply wasn't built to handle.

How to fix it: Replace the chain, and this time pay attention to the early warning signs (skip, slip, noise) before it gets to the breaking point. If you're running any motor or controller upgrades and keep snapping chains, the chain isn't really the problem at that point. The torque load is just too high for a chain drivetrain. That's the moment most riders start looking at a belt drive conversion, and it usually solves the problem permanently.

The freewheel factor

A lot of Razor MX650 drivetrain issues that look like chain problems are actually freewheel problems. The rear wheel on the MX650 uses a freewheel mechanism with internal pawls and springs that allow the wheel to coast when you're off-throttle. When the freewheel wears out or its springs weaken, it stops engaging reliably and you get symptoms that feel exactly like chain skip or chain slip, because power just isn't getting to the wheel properly.

The Razor freewheel is known for being on the weaker side from the factory. Aggressive riding and higher-torque motor setups accelerate the wear significantly. many decide to weld the freewheel for smoother and more durable riding. 

How to tell the difference: Lift the rear wheel off the ground and spin it by hand in reverse while the motor is off. A healthy freewheel clicks and resists. If it spins freely in both directions or feels sloppy and loose, the freewheel is worn. You can also try riding and noting whether the rear wheel engagement feels inconsistent when you apply throttle from a stop, which is different from chain skip that tends to happen at speed under load.

Freewheel welding (for belt drive builds especially) is a separate job, but it's worth ruling out before you replace expensive chain components.

The permanent fix: converting to belt drive

If you've fixed the chain, replaced the sprockets, tightened the tensioner, and still find yourself dealing with the same issues every few months, it's worth stepping back and asking whether the chain is really the right drivetrain for the build you have.

A belt drive conversion kit replaces the entire chain system with an HTD timing belt running between a CNC machined front pulley and a carbon fiber infused rear pulley. It installs in 30 to 60 minutes, requires no frame cutting or welding, and eliminates the need for lubrication, regular tensioning, or sprocket replacements.

The belt doesn't stretch, doesn't rust, and doesn't snap under the torque loads that kill stock chains. It's not the right choice for every rider (we cover that honestly in our belt drive worth it guide), but for anyone who mods their bike and rides it hard, it's usually the last drivetrain decision they have to make for a long time.

FAQ

How long does a Razor MX650 chain last?

On a stock bike ridden normally, a chain can last a year or more with proper maintenance. On a modded bike ridden hard, you might go through a chain every few months. If you're replacing chains that often, it's worth looking at a belt drive conversion instead.

What chain size does the Razor MX650 use?

The stock Razor MX650 uses a 25H chain. Make sure any replacement chain matches this spec.

Can I use any chain lubricant?

Stick to a proper chain lube, not WD-40. WD-40 is a water displacer and degreaser, not a lubricant. It'll actually strip the lube out of the chain over time and make things worse. A spray chain wax or dedicated bike chain oil is the right product.

Why does my chain keep coming off even after I tighten the tensioner?

Check the motor mount bolts first. A motor that has shifted slightly in its bracket is the most common cause of a chain that keeps derailing even with a properly adjusted tensioner. Tighten all the motor mount bolts and see if that solves it before assuming the tensioner is the problem.

Is it safe to ride with a loose chain?

No. A loose chain can jump the sprocket and jam in the wheel or frame, which can lock up the rear wheel mid-ride. Fix the tension before you ride again.

My motor runs but the chain doesn't move. What's happening?

This is almost always a freewheel issue. The motor is spinning but the freewheel isn't engaging and transferring power to the chain. Lift the rear wheel and run the motor slowly. If the wheel doesn't spin up with the motor, the freewheel is the problem, not the chain. Check that the internal pawls are engaging and that the freewheel hasn't worn or backed off the hub.

For a permanent solution to most of these headaches, take a look at the MxMods Belt Drive Kit, or read our full belt drive conversion guide to see if it makes sense for your build.