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 ", Always have
seat narrower than valve face. Follow engine manufacturer's recommen-
dations 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.
Sticking
Valves
When conditions such as carbon, misalignment 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.
S t e m s and Guides
Always check valve stems and guides for wear. Use go and no go
gages, if available. Scrap and replace valves and guides worn exces-
sively. 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 misalignment and bad seating, resulting in fast valve and seat
wear. When clearance with stem exceeds original clearance by0.002",
generally speaking, replace either valve or guide or both, as may be
Always
necessary.
regrind seat to make concentric to newly installed guide.
Valve Springs
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.
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