S&S Worldwide Motorcycle Accessories - Manual (Page 11)

12. Piston to Head & Piston to Valve Clearancing
NOTES:
●
The clearancing operations described in this section can be
done simultaneously as the same set-ups are used. Please
read this entire section before beginning work.
● All valve spring spacing, rocker arm to collar and rocker arm
to rocker cover clearancing must be done before piston to
valve clearancing can be checked.
● S&S ® flat topped pistons have sufficient valve clearance
when used with most street high performance cams with lifts
up to .525". However, we recommend that valve clearancing
be checked if other than stock cam is used.
● If S&S cylinder heads and pistons are used, cams of up to
.560" lift can be run without valve to piston clearance
problems. If cams with higher lift are used this clearance
must be checked.
Improper installation of pistons may cause unwarranted
stress, premature wear and/or contact with each other or
other engine components resulting in damage to pistons or
other engine parts.
● If there is any resistance or contact at any point in rotation it
must be diagnosed and corrected. Since it is nearly
impossible to anticipate every possible engine combination,
it is the engine builder’s responsibility to check for proper
running clearances. S&S considers checking and establishing
all running clearances as standard engine building practice
that must be performed during engine assembly. Engine
failure due to improper clearances between moving parts is
not covered under warranty.
Contact between moving engine components may cause
damage or destruction of the parts involved and produce
abrasive particles which may cause damage or premature
wear to other engine components.
A. Piston to head (squish) clearance
1.
Assemble engine with exception of cylinder heads.
NOTE: Pinion Shafts included with S&S flywheels kits and
assemblies for Evolution
® Sportster ® models are of the 1987 type.
This means that 1986 crankcases must be converted to use the
1987 and later style caged roller pinion main bearing assembly,
and that 1986-1987 style pinion gear and oil pump drive gears
must be used in 1988 and later engines. See step 6.
2. Rotate flywheels so front piston is positioned at top
dead center.
3. Note where piston deck (See Figure 5, piston deck
diagram) is positioned in relationship to head
gasket surface. Piston deck (flat located just above
top compression ring groove), not dome, must be
flush with or slightly below gasket surface.
4. If piston deck is higher than cylinder at top dead
center, something is wrong and S&S should be
notified. If piston deck position is correct proceed
to Step B.
NOTE: Most stock V-Twin and S&S engines are designed with
.045" to .062" piston to head clearance. This clearance is
provided by thickness of head gasket. Therefore at top dead
center, piston deck should be flush with or slightly below head
gasket surface of cylinder. Cylinder base gasket must be in place
when this check is made.
Insufficient clearance between piston domes and cylinder
heads will cause damage to pistons and heads.
B. Piston to Valve Clearance
1.
Turn engine over until piston in front cylinder is at
top dead center. Paint area around valve pockets
on pistons with machinist’s blue.
2. Place valves in cylinder head leaving off springs and
retainers. Place head on cylinder and secure with
one bolt.
3. Lower valves until they contact piston. Rotate valve
marking painted area.
4. Remove head and check points of contact. Valve
should fit in recessed area machined in piston dome.
NOTE: S&S recommends at least .060" clearance around
periphery of valve.
5. If insufficient clearance exists, remove piston and
grind valve pocket until head of valve fits flush
with proper clearance. Clean parts thoroughly
before reassembly.
Do not remove more material than needed when performing
piston to valve clearancing. Removal of excessive amounts of
material may weaken top ring land of piston causing piston
breakage and serious engine damage.
6. Repeat procedure for other cylinder head.
7. Spread layer of putty into valve pockets in both
pistons.
11
CAUTION
Figure 5
CAUTION
CAUTION
CAUTION