# Drive & Transmission Diagnosing chain, sprocket, tensioner and drivetrain faults on CEMOTO D-series electric dirt bikes. --- ## How the D-series drivetrain is arranged The D-series uses a hub motor with a **chain final drive** from the motor output to the rear wheel. The chain runs to a rear sprocket, and a **tensioner pulley** maintains tension on the run. This is a simple, serviceable arrangement — and almost all drivetrain problems are tension, lubrication or wear. --- ## Chain tension | Item | Value | | --- | --- | | **Correct chain slack** | Approximately **15 mm** | ### Adjusting chain tension Reproduced from the owner manual: 1. Loosen the **rear axle nuts**. 2. Adjust the **chain tension screw** until the chain slack is correct (approximately 15 mm). 3. Confirm the wheel remains aligned in the swing arm — a misaligned wheel causes the chain to run off the sprocket and wears the tire unevenly. 4. **Tighten the rear axle nuts.** > **Correctly tighten the rear axle.** An under-torqued rear axle will move under drive load, changing chain tension and potentially locking the rear wheel. Replace the axle nut if its self-locking feature is worn. --- ## Symptom: the motor runs but the bike does not move This points to the drive, not the motor. Check: 1. **Broken chain.** Inspect the chain along its full length. 2. **Chain off the sprocket.** A slack or misaligned chain can derail. 3. **Sprocket failure.** Check for broken or worn teeth. Hooked teeth indicate the sprocket is worn out. 4. **Tensioner pulley.** Confirm the pulley turns freely and is not seized — a seized pulley will not maintain tension. 5. **Freewheel / hub failure.** If the chain and sprockets are intact but the wheel does not turn, the fault is internal to the hub. This requires professional service. 6. **Motor shaft splines or keyway.** Stripped splines on the motor output allow the motor to spin without driving the chain. This is usually accompanied by noise. --- ## Symptom: noise from the drivetrain Reproduced from the owner manual: | Possible cause | Solution | | --- | --- | | **Chain drying** | Apply lubricant to the chain | | **Motorcycle is overloaded** | Do not exceed the rated load limit | Further causes: | Sound | Likely cause | | --- | --- | | **Rhythmic clicking, once per chain revolution** | A stiff or seized link; a damaged link should be replaced | | **Continuous whirring** | Chain too tight — this loads the motor bearings and should be corrected immediately | | **Slapping under acceleration** | Chain too loose | | **Rattle at the rear** | Worn sprocket, or a loose tensioner | | **Scraping that scales with motor speed, not wheel speed** | Motor or controller fault, not the drivetrain — see [Motor & Controller Faults](https://help.cemotoride.com/link/333) | --- ## Symptom: chain jumps or skips under acceleration 1. **Chain tension.** Slack allows the chain to ride up on the sprocket teeth. 2. **Worn sprocket.** Hooked or pointed teeth allow the chain to skip. Replace the sprocket and, normally, the chain at the same time — a new chain on a worn sprocket wears rapidly. 3. **Worn chain.** A chain that has stretched beyond its service limit no longer meshes correctly. Chains do not "stretch" — the pins and rollers wear, increasing pitch. 4. **Misalignment.** Confirm the rear wheel is square in the swing arm. --- ## Symptom: the bike is noisy when I stop pedalling (eBikes) This is characteristic of a freewheel or clutch issue rather than the chain. On eBikes with a derailleur drivetrain, check the derailleur adjustment and chain line as well. --- ## Lubrication and cleaning | Task | Frequency | Notes | | --- | --- | --- | | **Lubricate the chain** | After riding in wet or dusty conditions, and whenever the chain appears dry | Use a chain lubricant suited to your conditions. Wipe off excess — surplus lubricant attracts grit | | **Clean the chain** | As needed | A dry brush first; avoid aggressive solvents that strip factory lubricant from inside the rollers | | **Inspect chain wear** | Regularly | Check for stiff links, rust and elongation | | **Check tension** | Frequently | Approximately 15 mm slack | | **Inspect the sprocket** | With each chain service | Look for hooked, sharp or missing teeth | **After off-road riding:** clean the chain, the sprockets and the tensioner pulley of mud and grit. Grit is the primary cause of accelerated drivetrain wear. --- ## Wear components and warranty The following are **wear-and-tear parts and are excluded from warranty**: - Chains and sprockets - Tensioner pulley - Bearings and cables - Rubber seals and grips They are available as replacement parts at cost — see [Spare Parts & Compatibility](https://help.cemotoride.com/link/382). --- ## Related parts CEMOTO supplies these D-series drivetrain components as spare parts: | Part | | --- | | D03 chains for dirt bike | | D03 tensioner pulley | | D03 dirt bike motor | | D03 motor protection cover | | D03 front / rear axle sleeve | See [Spare Parts & Compatibility](https://help.cemotoride.com/link/382) for the full catalog and how to confirm compatibility with your model. --- ## Related pages - [Motor & Controller Faults](https://help.cemotoride.com/link/333) - [Maintenance Schedule](https://help.cemotoride.com/link/323) - [Spare Parts & Compatibility](https://help.cemotoride.com/link/382) - [Technical Guides](https://help.cemotoride.com/link/336)