Valve & Valve Guide Servicing

NOTE: When reconditioning valves, ensure interference angles of valve and seat are not lapped out. Remove grooves and/or score marks from end of valve stem with oil stone. DO NOT remove more than .010" (.254 mm) from valve stem end.

To check valve guide wear, insert valve with head positioned 1/16" above seat. Attach dial indicator to cylinder head. Position dial indicator stem against valve stem just above guide.
Move valve in guide and measure wear shown on indicator. If guide wear is excessive, ream to next oversize. Service valves are available in standard, .003", .015" and .030" oversize.
Clean valve guides. Reface valve seat if guide is reamed. If valve seat face is reground, check margin width dimension.
Check seats for proper angle and width. Measure valve seat runout. Runout should be within .002" (.05 mm) for intake and exhaust.
Use scraper to break (lightly chamfer or bevel) sharp top inside edge of guide. After guide repair, inspect valve stem end for wear. Valve stem end may be reconditioned by grinding to proper dimension at 90° angle.
Check valve head for warpage. DO NOT reface if knife edge will result. Knife edges lead to breakage, burning or pre-ignition due to heat localizing on edge. Replace if edge of valve head is less than .031" (.79 mm) thick after grinding.
When new valves are installed or after grinding, measure valve stem height. Ensure that there is at least .015" (.381 mm) minimum clearance between gauge surface and end of valve stem. Ensure that distance between gauge surface and spring retainer is .030" (.76 mm) minimum.
If gauge-to-stem clearance is less than specification, remove valve and grind tip of stem at 90° angle for clearance. Note that valve stem with less than .005" (.13 mm) above spring retainer is too short and must be replaced.