159274-1920 ZEXEL 9 421 610 170 BOSCH STOP PIN 9421610170 1592741920 8941722980

Cylinder Head And Valve Components
Check cylinder head for cracks before reconditioning.Flatness of the cylinder head should be within .006 in. (0.15 mm) total, and a maximum of .003 in. (0.08 mm) for any 6 in. (152.4 mm) span. A maximum stock removal of .010 in. (0.25 mm) is permissible when resurfacing the head.Always check the thickness of a cylinder head before resurfacing. The cylinder head may have been resurfaced before and would not have enough stock to be resurfaced again.To check the thickness of a cylinder head, measure through the fuel injection nozzle holes at each end of the cylinder head. For the correct thickness of the cylinder head, see the topic CYLINDER HEAD in the SPECIFICATIONS.The exhaust valve seats have replaceable inserts. To remove, use the 8S7170 Valve Seat Insert Puller Group.
REMOVING EXHAUST VALVE SEAT INSERTFreeze the exhaust valve seat inserts or use the 8S7170 Valve Seat Insert Puller Group to install inserts into head. Be sure bores are clean, free of burrs, and the insert has a good press fit into the bore.After inserts are installed, grind the seat face of the insert to be sure it is flat, has the correct angle, and is in alignment with the bore in the valve guide. For specifications, see VALVE GRINDING SPECIFICATIONS CHART. Replace exhaust valve seat inserts when valve seat width or valve head-to-cylinder head face can not be machined to the correct specification. For specifications, see VALVE GRINDING SPECIFICATIONS CHART.A 2N8943 Valve Seat Insert for the intake valve is available. This insert can be used in the repair of cylinder heads which have an intake valve seat with damage. Before, damage to an intake valve seat made replacement of the cylinder head assembly necessary.To use a 2N8943 Valve Seat Insert, the inlet port of the cylinder head must be machined to a diameter of 2.1470 .0005 in. (54.534 0.013 mm) and to a depth of .442 .002 in. (11.23 0.05 mm).To install a 2N8943 Valve Seat Insert into the cylinder head, freeze the insert or use a 2P2343 Extractor with the 8S7170 Valve Seat Insert Puller Group. After an insert is installed, grind the seat face of the insert to be sure it is flat, has the correct angle, and is in alignment with the bore in the valve guide. For specifications, see VALVE GRINDING SPECIFICATIONS CHART.Clean valve guides of all carbon and oil, using the 5P5176 Brush and a solvent.The valve guides are cast in the cylinder heads. Check each valve guide bore size 3/4 in. (19.1 mm) deep from each end. The bore size is .3745 .0005 in. (9.512 0.013 mm) and the maximum size worn is .3760 in. (9.550 mm). Valve guides worn more than the maximum wear size, can be restored to original tolerances through knurling.Use the 5P3536 Valve Guide Gauge Group to check the bore of the valve guides. Special Instructions GMG02562 gives complete and detailed instructions for use of the 5P3536 Valve Guide Gauge