Yamaha SR400 2014 Service Manual

VALVES AND VALVE SPRINGS5-19EAS24300CHECKING THE VALVE SEATSThe following procedure applies to all of thevalves and valve seats.1. Eliminate:• Carbon deposits(from the valve face and valve seat)2. Check:• Valve seatPitting/wear  Replace the cylinder head.3. Measure:• Valve seat width “a”Out of specification  Replace the cylinderhead.▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼a. Apply blue layout fluid “b” onto the valve face.b. Install the valve into the cylinder head.c. Press the valve through the valve guide andonto the valve seat to make a clear impres-sion.d. Measure the valve seat width.TIPWhere the valve seat and valve face contactedone another, the blue layout fluid will have beenremoved.▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲4. Lap:• Valve face• Valve seatTIPAfter replacing the cylinder head or replacing thevalve and valve guide, the valve seat and valveface should be lapped.▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼a. Apply a coarse lapping compound “a” to thevalve face.NOTICEECA13790Do not let the lapping compound enter thegap between the valve stem and the valveguide.b. Apply molybdenum disulfide oil onto thevalve stem.c. Install the valve into the cylinder head.d. Turn the valve until the valve face and valveseat are evenly polished, then clean off all ofthe lapping compound.Valve seat width (intake)1.30 mm (0.0512 in)Limit1.6 mm (0.06 in)Valve seat width (exhaust)1.30 mm (0.0512 in)Limit1.6 mm (0.06 in)