Jeep Engines - Oljeep

4.2L IN-LINE 6 (CAMSHAFT AND VALVE GEAR) 305VALVE GUIDESThe valve guides are an integral part of the cylinder headand are not replaceable. When the stem-to-guide clearanceis excessive, the valve guide bores must be reamed toaccommodate the next larger oversize valve stem. Reamvalve guide bores in steps, starting with a 0.0762 mm(0.003") oversize reamer and progress to the size required.Valve Stem-to-Guide Clearance MeasurementValve stem-to-guide clearance may be measured by eitherof the following two methods.1. Preferred Methoda. Remove the valve from the head. Refer to Valveand Valve Spring Removal - Cylinder HeadRemoved, in this section, for the procedure.b. Clean the valve stem guide bore with solvent and abristle brush.c. Insert the telescoping gauge into the bore of thevalve stem guide approximately 9.525 mm (375")from the valve spring side of the head with contactscrosswise to the cylinder head.d. Remove and measure the telescoping gauge with amicrometer.e. Repeat the measurement with contacts lengthwiseto the cylinder head.f. Compare the crosswise to lengthwisemeasurements to determine out-of-roundness. Ifthe measurements differ by more than 0.0635 mm(0.0025"), ream the guide bore to accommodate theoversize valve stem.g. Compare the measured valve guide bore diameterwith the diameter listed in 4.2L EngineSpecifications, 'Engine Assembly' section of thischapter. If the measurement differs from thespecification by more than 0.0762 mm (0.003"),ream the guide bore to accommodate the oversizevalve stem.2. Alternate Methoda. Use a dial indicator to measure the lateralmovement of the valve stem (stem-to-guideclearance) with the valve installed in its guide andjust off the valve seat. The correct clearance is0.00250.0762 mm (0.001-0.0031').b. If the indicated movement exceeds thespecification, ream the guide bore to accommodatean oversize valve stem.VALVE TIMING1.2.3.4.5.6.7.Disconnect the spark plug wires and remove the sparkplugs.Remove the cylinder head cover. Refer to CylinderHead Cover Removal, 'Cylinder Head' section of thischapter, for the procedure.Remove the capscrews, bridge and pivot assembly, androcker arms from above the No. 1 cylinder.Alternately loosen each capscrew, one turn at a time, toavoid damaging the bridge.Rotate the crankshaft until the No. 6 piston is at topdead center (TDC) on the compression stroke.Rotate the crankshaft counterclockwise (viewed fromthe front of the engine) 90".Install a dial indicator on the end of the No. 1 cylinderintake valve pushrod. Use rubber tubing to secure theindicator stem on the pushrod.8. Set the dial indicator pointer at zero.9. Rotate the crankshaft clockwise (viewed from the frontof the engine) until the dial indicator pointer indicates0.305 mm (0.012") travel distance (lift).10. The timing notch index on the vibration damper shouldbe aligned with the TDC mark on the timing degreescale.1 1. If the timing notch is more than 13 mm (1/2") awayfrom the TDC mark in either direction, the valvetiming is incorrect.12. If the valve timing is incorrect, the cause may be abroken camshaft pin. It is not necessary to replace thecamshaft because of pin failure. A spring pin isavailable for service replacement.