What Causes Abnormal Noise in the Scooter Transmission Case?

[DeEmery]

Here are the specific reasons for abnormal noise in the scooter transmission case: Noise only present during idle or low-speed operation: Causes include excessive clearance between the piston and cylinder wall; piston pin or connecting rod bearing installed too tightly; excessive clearance between the tappet and its guide hole; wear on the camshaft profile; loose starter clutch causing pulley noise, especially noticeable during speed changes. Disordered noise at a certain speed, with brief sounds occurring successively during rapid deceleration: Causes include cracked camshaft timing gear or loose fixing nut; broken crankshaft; loose piston pin bushing; excessive axial clearance of the camshaft or loose bushing. Noise appearing during rapid acceleration and persisting during high-speed operation: Causes include loose connecting rod bearings, melted or mismatched bearing shells; loose crankshaft bearings or melted bearing shells; broken piston pin; broken crankshaft.

[Lester]

With years of motorcycle repair experience, the most common causes of abnormal noise in the transmission case are chain slack or bearing damage. Over time, the chain stretches and makes a clicking sound when slipping; if the bearing is rusty or lacks lubrication, it will squeak continuously. Sometimes, it's gear wear that causes a rattling noise during acceleration. Lubrication is crucial—when the oil dries up, friction increases, leading to abnormal noises. Additionally, dust entering the case or moisture corrosion can amplify the noise. A cracked or aged drive belt can also cause this. I've heard from customers many times that delaying repairs can accelerate part failure, costing a lot for replacements. It's recommended to regularly maintain and lubricate the chain, and if noise appears, take it to a professional shop for inspection—don't wait until it becomes a major issue. Safety comes first. Adding lubricant yourself is simple, but if the noise is unusual, avoid disassembling it randomly to prevent further damage.