What are the causes of abnormal noise in motorcycle idle speed?
3 Answers
Motorcycle idle speed abnormal noise may be caused by excessive valve clearance leading to abnormal sound; excessive clearance between the small end of the crankshaft connecting rod and the piston pin; crankshaft bearing damage; other transmission faults and loose screws causing loose connections between motorcycle components. Piston slap is caused by wear between the cylinder and piston, resulting in increased clearance, especially when the piston skirt is worn, the knocking sound will be very obvious. The noise will also increase when the engine is cold or under heavy load. Piston slap is caused by the increased clearance between the piston and cylinder, so compression will also deteriorate, engine power will decrease, wear will intensify, and noise will increase. Solutions: After the engine starts, if there is a knocking sound during low-temperature operation and the sound disappears when the temperature normalizes, it can be left untreated and continue to operate. When the engine temperature is normal and there is obvious knocking sound, high-speed operation should be avoided as much as possible, and disassembly and repair should be carried out as soon as possible. After removing the cylinder head and pulling out the piston, if severe cylinder ovality, scoring, or excessive clearance between the piston and cylinder are found, replacement should be performed, including the cylinder liner, piston, and piston rings. If the connecting rod is found to be deformed, it should be replaced as much as possible.
When it comes to abnormal noises during motorcycle idling, I often hear fellow riders mention this issue. In reality, there are quite a few root causes. The most common one is a loose chain, which produces squeaking or rattling sounds as it wobbles during idling. Chain wear or lack of lubrication can worsen the problem. Another cause is excessive valve clearance, where the knocking sound of the valves becomes noticeable at low idle speeds, creating an annoying ticking noise. Loose exhaust pipe joints can also cause resonant noises, especially in older bikes where screws tend to loosen. More seriously, worn crankshaft bearings can produce a dull grinding sound from the bottom of the engine, and neglecting this could affect the engine's lifespan. I recommend first checking the chain tension by shaking it manually to see if it's loose—if it is, tighten it and add some chain lubricant. If the noise comes from inside the engine, consult a professional mechanic to inspect the valves or bearings. Don’t underestimate idling noises; ignoring them long-term can increase repair costs. Regular maintenance can save you a lot of trouble.
From my experience, don't ignore idle speed abnormal noises. The chain tends to squeak when it's dry - last time I sprayed some chain oil myself and it became much quieter. Improper valve adjustment can also cause clicking sounds, and unstable idle RPM reveals the issue. Loose exhaust pipe bolts are common too, causing annoying buzzing resonance at idle. Worn clutch or excessive drivetrain component clearance may produce friction noises too. Simple maintenance like chain cleaning and lubrication can prevent most minor issues. Though idle noises seem small, prolonged neglect accelerates wear and leads to costly overhauls eventually. Remember, keeping components clean and properly lubricated is key. Riders with DIY skills can try adjusting the chain themselves.
