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7. CYLINDER HEAD/VALVES

7-0

Mongoose/KXR 250

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CYLINDER HEAD/VALVES

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SERVICE INFORMATION -------------------------------------------- 7- 2

TROUBLESHOOTING ------------------------------------------------- 7- 3

CYLINDER HEAD COVER-------------------------------------------- 7- 4

CAMSHAFT/CAMSHAFT HOLDER --------------------------------- 7- 4

CYLINDER HEAD------------------------------------------------------ 7- 9

Summary of content (13 pages)

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7. CYLINDER HEAD/VALVES Mongoose/KXR 250 SERVICE INFORMATION GENERAL INSTRUCTIONS • The cylinder head can be serviced with the engine installed in the frame. • When assembling, apply molybdenum disulfide grease or engine oil to the valve guide movable parts, valve arm and camshaft sliding surfaces for initial lubrication. • The camshaft is lubricated by engine oil through the cylinder head engine oil passages. Clean and unclog the oil passages before assembling the cylinder head.
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7. CYLINDER HEAD/VALVES TORQUE VALUES Cylinder head cover bolt Cam shaft hold nut Tappet adjusting nut 0.8_ 1.2kgf-m 2.3_ 2.7kgf-m 0.7_ 1.1kgf-m SPECIAL TOOLS Valve spring compressor Tappet adjuster Mongoose/KXR 250 Apply engine oil to threads E040 E012 TROUBLESHOOTING • The poor cylinder head operation can be diagnosed by a compression test or by tracing engine top-end noises.
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7. CYLINDER HEAD/VALVES CYLINDER HEAD COVER Mongoose/KXR 250 Oil Recycle Tube REMOVAL Remove fuel tank. (Refer to the chapter 5) Disconnect the oil recycle tube at the cylinder head cover. Remove the four bolts at the cylinder head cover, then remove the cylinder head cover. Cylinder Head Cover Bolts O-ring INSTALLATION Install a new cylinder head cover O-ring and install the cylinder head cover. Install and tighten the cylinder head cover bolts. Torque: 0.8_ 1.
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7. CYLINDER HEAD/VALVES Mongoose/KXR 250 Remove the four camshaft holder nuts and washers. °ØDiagonally loosen the cylinder head nuts in 2 or 3 times. Remove the camshaft holder and dowel pins. Nuts and Washers Camshaft Holder Camshaft Remove the camshaft gear from the cam chain and remove the camshaft. CAMSHAFT HOLDER DISASSEMBLY Take out the valve rocker arm shafts. Remove the valve rocker arms, arm shafts and stop plate.
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. CYLINDER HEAD/VALVES CAMSHAFT HOLDER INSPECTION Inspect the camshaft holder for wear or damage. Mongoose/KXR 250 Camshaft Holder Inspect the rocker arm shaft for blue discoloration or grooves. If any defects are found, replace the rocker arm shaft with a new one, then inspect lubrication system. Rocker Arm Shafts Rocker Arm Bore Inspect the rocker arm bore, cam lobe contact surface and adjuster surface for wear/pitting/scratches/blue discoloration.
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7. CYLINDER HEAD/VALVES Mongoose/KXR 250 CAMSHAFT HOLDER ASSEMBLY Reverse the “CAMSHAFT HOLDER DISASSEMBLY” procedures. °ØAlign the cross cutout on the exhaust valve rocker arm shaft with the bolt of the camshaft holder. CAMSHAFT INSPECTION 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. Inspect camshaft lobes for pitting/scratches/blue discoloration. Measure the cam lobe height. Service Limits: IN : 34.
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7. CYLINDER HEAD/VALVES Mongoose/KXR 250 INSTALLATION Reverse the “CAMSHAFT REMOVAL” procedures. Note the following points: 1. Turn the 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 camshaft onto the cylinder head.
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7. CYLINDER HEAD/VALVES Mongoose/KXR 250 Intake Manifold CYLINDER HEAD REMOVE Remove the camshaft. (Refer to the “camshaft remove” section in the chapter 7) Remove the carburetor. (Refer to the “carburetor remove” section in the chapter 5) Remove the exhaust muffler. (Refer to the “exhaust muffler remove” section in the chapter 2) Bolts Remove the two bolts and then remove the carburetor intake manifold. Bolts Bolt Remove the bolt and disconnect the thermostat. Remove the two cylinder head bolts.
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7. CYLINDER HEAD/VALVES Mongoose/KXR 250 VALVE /VALVE GUIDE INSPECTION Inspect each valve for bending, burning, scratches or abnormal stem wear. If any defects are found, replace the valve with a new one. Check valve movement in the guide. Measure each valve stem O.D. Measure each valve guide I.D. Subtract each valve stem O.D. from the corresponding guide I.D. to obtain the stemto-guide clearance. Service limits: IN : 0.06mm replace if over EX: 0.
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7. CYLINDER HEAD/VALVES Measure compressed force (valve spring) and installed length. Replace if out of specification. Service limits: IN : 10.20_ 11.84kg(at 18.05mm) EX : 19.14_ 22.02kg(at 21.5mm) Measure the spring tilt. Replace if out of specification. Service limits: IN : 0.8mm EX : 1.
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7. CYLINDER HEAD/VALVES Mongoose/KXR 250 ASSEMBLY Install the valve spring seats and oil seal. °ØBe sure to install new oil seal. Lubricate each valve with engine oil and insert the valves into the valve guides. Install the valve springs and retainers. Compress the valve springs using the valve spring compressor, then install the valve cotters. °Ø• When assembling, a valve spring compressor must be used. • Install the cotters with the pointed ends facing down from the upper side of the cylinder head.