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6. CYLINDER HEAD/VALVES

6-0

YUP 25 0

6 .

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CYLINDER HEAD/VALVES

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SCHEMATIC DRAWING ---------------------------------------------- 6- 1

SERVICE INFORMATION -------------------------------------------- 6- 2

TROUBLESHOOTING ------------------------------------------------- 6- 3

CYLINDER HEAD COVER REMOVAL ----------------------------- 6- 4

CAMSHAFT REMOVAL----------------------------------------------- 6- 4

CYLINDER HEAD REMOVAL --------------------------------------- 6- 6

CYLINDER HEAD DISASSEMBLY --------------------------------- 6- 7

CYLINDER HEAD ASSEMBLY -------------------------------------- 6- 8

CYLINDER HEAD INSTALLATION -------------------------------- 6- 9

CAMSHAFT INSTALLATION---------------------------------------- 6-10

CYLINDER HEAD COVER INSTALLATION ---------------------- 6-11

Summary of content (12 pages)

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6. CYLINDER HEAD/VALVES YUP 250 6.
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6.
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6. CYLINDER HEAD/VALVES YUP 250 SERVICE INFORMATION GENERAL INSTRUCTIONS • The cylinder head can be serviced with the engine installed in the frame. Coolant in the radiator and water jacket must be drained first. • When assembling, apply molybdenum disulfide grease or engine oil to the valve guide movable parts and valve arm sliding surfaces for initial lubrication. • The valve rocker arms are lubricated by engine oil through the cylinder head engine oil passages.
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6. CYLINDER HEAD/VALVES YUP 250 TROUBLESHOOTING • The poor cylinder head operation can be diagnosed by a compression test or by tracing engine top-end noises.
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6. CYLINDER HEAD/VALVES YUP 250 Cylinder Head Cover CYLINDER HEAD COVER REMOVAL Remove the met-in box (!2-6) and center cover. (!2-7) Remove two nuts and four bolts on the cylinder head. Place the scooter on its side stand for remove the cylinder head cover. Nuts Oil Vapor Recovery Tube CAMSHAFT REMOVAL Turn the A.C. generator flywheel so that the “T” mark on the flywheel aligns with the index mark on the crankcase.
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. CYLINDER HEAD/VALVES YUP 250 Cam Chain Remove the camshaft gear from the cam chain to remove the camshaft. Camshaft Gear CAMSHAFT INSPECTION Check each cam lobe for wear or damage. Measure the cam lobe height. Service Limits: IN: 34.14mm replace if below EX:34.02mm replace if below Camshaft Bearings Check each camshaft bearing for play or damage. Replace the camshaft assembly with a new one if the bearings are noisy or have excessive play.
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6. CYLINDER HEAD/VALVES YUP 250 Camshaft Holder CAMSHAFT HOLDER INSPECTION Inspect the camshaft holder, valve rocker arms and rocker arm shafts for wear or damage. ＊ If the valve rocker arm contact surface is worn, check each cam lobe for wear or damage. Rocker Arm Shafts Measure the I.D. of each valve rocker arm. Service Limits: IN: 10.10mm replace if over EX: 10.10mm replace if over Measure each rocker arm shaft O.D. Service Limits: IN: 9.90mm replace if below EX: 9.
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6. CYLINDER HEAD/VALVES YUP 250 Cylinder Head CYLINDER HEAD DISASSEMBLY Remove the valve spring cotters, retainers, springs, spring seats and valve stem seals using a valve spring compressor. ＊• Be sure to compress the valve springs with a valve spring compressor. • Mark all disassembled parts to ensure correct reassembly. Special Combustion Chamber Valve spring compressor E040 Valve Spring Compressor Remove carbon deposits from the exhaust port and combustion chamber.
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6. CYLINDER HEAD/VALVES YUP 250 Straight Edge INSPECTION CYLINDER HEAD Check the spark plug hole and valve areas for cracks. Check the cylinder head for warpage with a straight edge and feeler gauge. Service Limit: 0.05mm repair or replace if over Feeler Gauge VALVE SPRING FREE LENGTH Measure the free length of the inner and outer valve springs. Service Limits: Inner (IN, EX) : 29.5mm replace if below Outer (IN, EX): 39.
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6. CYLINDER HEAD/VALVES YUP 250 Plastic Hammer Tap the valve stems gently with a plastic hammer to firmly seat the cotters. ＊ Be careful not to damage the valves. Cylinder Head Gasket CYLINDER HEAD INSTALLATION Install the cam chain guide. Install the dowel pins and a new cylinder head gasket. Cam Chain Guide Install the cylinder head and take out the cam chain Assemble the camshaft holder. First install the intake and exhaust valve rocker arms; then install the rocker arm shafts.
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6. CYLINDER HEAD/VALVES YUP 250 Punch Marks CAMSHAFT INSTALLATION Turn the A.C. generator flywheel so that the “T” mark on the flywheel aligns with the index mark on the crankcase. Keep the round hole on the camshaft gear facing up and align the punch marks on the camshaft gear with the cylinder head surface (Position the intake and exhaust cam lobes down.) and install the cam chain over the camshaft gear. Round Hole Cam Chain Install the dowel pins.
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6. CYLINDER HEAD/VALVES YUP 250 Tensioner Screw Turn the cam chain tension screw counter clockwise to release it. O-ring Apply engine oil to a new O-ring and install it. Tighten the cam chain tension cap screw. ＊ Be sure to install the gasket into the groove properly. Cylinder Head Cover CYLINDER HEAD COVER INSTALLATION Adjust the valve clearance. (!3-6) Install a new cylinder head cover O-ring and install the cylinder head cover. ＊ Be sure to install the O-ring into the groove properly.