- Insufficient air intake
- Piston ring failure
- Damaged crank bearings
- Timing chain slap
To determine the exact cause of the knocking sound, you'll need to inspect your engine.
Insufficient Air Intake
If the engine is not getting enough air, it can cause the fuel mixture to be too rich, which can lead to knocking. Check the air filter to ensure it is clean; you may also want to inspect the intake manifold for leaks.
Piston Ring Failure
Piston ring failure can also cause knocking sounds. Piston rings seal the combustion chamber, preventing air and fuel from leaking past the piston. When piston rings fail, they can allow combustion gases to escape, creating a knocking sound. To check for piston ring failure, you'll need to remove the cylinder head and inspect the piston rings.
Damaged Crank Bearings
Damaged crank bearings can also cause knocking sounds. Crank bearings support the crankshaft, allowing it to rotate smoothly. When crank bearings fail, they can cause the crankshaft to wobble, which can create a knocking sound. To check for damaged crank bearings, you'll need to inspect the crankshaft and bearing surfaces.
Timing Chain Slap
Timing chain slap is another potential cause of knocking sounds in an engine. The timing chain synchronizes the movement of the crankshaft and camshaft. When the timing chain is loose, it can slap against the timing chain cover, creating a knocking sound. To check for timing chain slap, you'll need to remove the timing chain cover and inspect the timing chain.
Recommendations
If you're not comfortable inspecting your engine, I recommend taking your Yamaha blaster to a qualified mechanic for diagnosis and repair.
