How to Adjust Valves on a Suzuki LT 125

The 1984 Suzuki LT125 ATV features a single-cylinder, air-cooled, overhead cam four-stroke engine. Suzuki recommends adjusting the valve clearances after the first 100 miles or one month of operation, and thereafter every 600 miles or six months. To assure proper tolerances, checking the clearance and adjusting the valves must be done only when the engine is cool to the touch. The correct valve clearance for the intake and exhaust valves on the four-stroke LT125 is 0.08 mm – 0.13 mm.



  • Lift the combination seat/rear fender assembly to access the engine. The intake (rear) valve is closest to you, the exhaust valve is located on the opposite side of the cylinder head, towards the front of the vehicle.

  • Expose the two valves by removing the threaded caps from the front and rear of the cylinder head of the engine with an end wrench. Threaded caps look like hexagonal bolt heads, but with a broad circular base. The caps cover wells in the cylinder heads which allow access to the valve adjustment screws. Remove the recoil starter from the left side of the engine by taking out the four bolts securing it to the crankshaft mount.

  • Remove the spark plug wire and take out the spark plug. Put your thumb over the spark plug hole and rotate the crankshaft by hand counterclockwise until you feel the sensation of pressure building inside the cylinder that indicates the piston is on its compression stroke. (If the piston is on an exhaust stroke, the exhaust valve will be open and there will be no detectable pressure in the cylinder at all.) The “T” mark on the crankshaft rotor should be lined up with the pointer on the crankcase.

Checking Valve Clearance

  • Select a feeler gauge within the 0.08 mm to 0.013 range.

  • Locate the intake valve at the rear of the engine and slip the feeler gauge between the valve and its corresponding adjusting screw.

  • Determine the fit of the feeler gauge. If it fits snugly with minimal metal-to-metal contact and can be moved in and out of the gap without binding, the valve adjustment is within limits. If the feeler gauge will not fit between the valve stem and the adjusting screw, the adjustment is too tight. If there is no feeling of drag as it is inserted in the gap and you can wiggle it laterally and up and down without resistance the valve gap is too loose.

Valve Adjustment And Reassembly

  • Loosen the locknut on the adjusting screw with an end wrench. Using a flat-bladed screwdriver, loosen the adjusting screw until the feeler gauge will fit into the gap or tighten it to remove excess play. Hold the adjusting screw in place with the screwdriver and tighten the locknut with the end wrench. Repeat the procedure on the exhaust valve at the front of the engine.

  • Re-install the threaded caps on the front and rear of the cylinder head. Bolt the recoil starter on crankshaft mount at the left side of the engine using the four bolts.

  • Replace the spark plug and attach the spark plug wire. Lower and latch the seat/fender assembly.

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