What Causes Abnormal Noises in a Scooter's Transmission Box?
2 Answers
Abnormal noises in a scooter's transmission box can be caused by the following reasons: 1. Noises occur only at idle or low speeds: Possible causes include excessive clearance between the piston and cylinder wall; overly tight piston pin or connecting rod bearing assembly; excessive clearance between the tappet and its guide hole; wear on the camshaft profile; or a loose starter clutch causing pulley noise, which becomes more noticeable when the speed changes. 2. Disordered noises at a certain speed, with brief sounds occurring successively during rapid deceleration: Possible causes include a cracked camshaft timing gear or loose fixing nut; broken crankshaft; loose piston pin bushing; or excessive axial clearance of the camshaft or loose bushing. 3. Noises appear during rapid acceleration and persist at high speeds: Possible causes include loose connecting rod bearings, melted or mismatched bearing shells causing rotation; loose crankshaft bearings or melted bearing shells; broken piston pin; or broken crankshaft.
I noticed abnormal noises coming from the scooter's transmission case, most commonly caused by belt aging or slipping. I remember during a long-distance ride, there was a squeaking sound when accelerating. Upon inspection, I found the belt was cracked and severely worn, so it needed immediate replacement to avoid breaking down midway. If pebbles or dust get stuck in the pulley, it can also cause friction noises—simply cleaning it out will do. Bearing damage is another major issue, producing a creaking sound, often due to insufficient lubrication and frequent use. Worn clutch springs can also lead to abnormal noises, especially noticeable at idle. I recommend regular maintenance—opening the transmission case periodically to check for dust buildup and lack of lubrication. In winter, lower temperatures reduce lubrication effectiveness, leading to more noise, so extra care is needed. Repair costs aren't high, but delaying fixes can damage core components.
