What is the standard valve clearance for a pushrod 125?
2 Answers
The intake valve clearance for a pushrod 125 is generally 0.05-0.07, and the exhaust valve clearance is 0.08-0.12. Function of valves: They are specifically responsible for introducing air into the engine and expelling exhaust gases after combustion. Structurally, they are divided into intake valves and exhaust valves. The intake valve's role is to draw air into the engine to mix with fuel for combustion; the exhaust valve's role is to expel the burned exhaust gases and dissipate heat. Conditions of too small and normal valve clearance: Too small valve clearance can cause difficulties in cold starts, unstable idle, and even damage components like the valve rocker arm and camshaft. Moreover, the optimal valve clearance is not determined by so-called 'silence' but by a comprehensive balance, ensuring normal operation in terms of starting, idling, power, and sound. The characteristics of pushrod engines mean they will always have some degree of tapping sound.
I've been repairing motorcycles for thirty years, and I know the valve clearance standards for a pushrod 125 like the back of my hand. When the engine is cold, the intake valve clearance should be between 0.05 to 0.08 millimeters, while the exhaust valve is recommended to stay within 0.08 to 0.10 millimeters. When adjusting with a feeler gauge, you must find the correct compression top dead center, then loosen the lock nut and slowly turn the adjusting screw. This job really tests your touch—if you set it too tight, the valve won't seal properly and will burn the valve seat; if it's too loose, you'll hear an annoying tapping noise. New bikes need their clearance checked every 5,000 kilometers, and older bikes even more frequently. Last week, I met a young guy who tried doing it himself and forcefully adjusted 0.1 to 0.2—the engine ended up sounding like a broken gong. Honestly, if you don't have professional tools, it's better to go to an experienced mechanic. After all, a difference of just a few microns can affect the entire engine's lifespan.
