Special POINTERS on VALVE RECONDITIONING
Valve Head Margin
Scrap and replace any valve that cannot be entirely refaced with definite margin maintained. The amount of grinding
necessary to true valve face is an indication of the head warpage from axis or centerline of its stem. With excessive
warpage, a knife edge will be ground on part or all of valve head due to the considerable amount of metal that must be
removed to completely reface. Heavy valve heads are required for strength and to dissipate heat. Knife edges lead to
breakage and burning, and to pre-ignition due to heat localizing on edge.
Width of Seat
The tendency is usually to grind seats too wide when reconditioning. The seat width in many engines should be less
than l/8". Always have seat narrower than valve face. Follow engine manufacturer's recommendations in this as in all
other technical matters. If necessary to narrow seat, use 15 stone. Seats too wide tend to collect carbon. Seats too
narrow prevent valve head from rapidly dissipating its heat to block. If new insert seat is installed, regrind to make
concentric to guide.
When conditions such as carbon, misalinement and excessive wear have been corrected, and valves persist in
sticking, it is a satisfactory remedy with most engine designs to cut guide off flush with block. Use drill bit slightly larger
than outside diameter of guide with point ground to 20 angle. Remove with small scraper any burr left on inner diameter
of guide. Other methods are to counterbore guide or grind relief on valve stem. Consult engine manufacturer for specific
Stems and Guides
Always check valve stems and guides for wear. Use "go" and "no go" gauges, if available. Scrap and replace valves
and guides worn excessively. Too much clearance in the intake guide admits air and oil into combustion chamber,
upsetting carburetion, increasing oil consumption, and making heavy carbon deposits. Sloppy exhaust guide clearance
causes misalinement and bad seating, resulting in fast valve and seat wear. When clearance with stem exceeds original
clearance by 0.002", generally speaking, replace either valve or guide or both, as may be necessary. Follow engine
manufacturer's recommendations. Always regrind seat to make concentric to newly installed guide.
Test valve springs for uniform strength. Use regular valve spring tester for accurate check-or place springs on end
upon level surface (see that spring ends are flat) and use any straight edge to determine irregularity in height. Unequal or
cocked valve springs will undo in the assembled job all the precision that has been put into it. Spring tension too weak
allows valves to flutter. Spring tension too heavy causes "stretched" valves. Either condition aggravates wear on valve
and seat with possible valve breakage.