Caution – S&S Cycle Replacement Cylinder Heads for 1984-1999 Harley-Davidson Evolution Engines and 1986-2003 Sportster Motorcycles User Manual

Page 4

Check Piston Alignment in Cylinder Bore
The purpose of this procedure is to check for and correct
possible piston misalignment in the cylinder bore. During
normal manufacturing, engine components such as
crankcases, cylinders, and connecting rods can be machined
to dimensions within factory specifications but on the
extreme ends of the tolerance range. Sometimes these
components when combined together form an assembly
that is borderline or actually "out of print". The worst result
is that the pistons can run cocked in the cylinder bores
causing the connecting rods to thrust to the sides exerting
unnecessary stress on the pistons, rings, rod bearings and
other related parts. This procedure is not the same as blue
printing, but it provides almost the same result. We feel that
not enough emphasis is given to checking the piston
alignment in the cylinder bore.

NOTE: All engines should be checked upon disassembly. This
applies to any engine receiving new pistons which includes those
being completely overhauled.

Pistons which do not run true in cylinder bores may cause
excessive connecting rod side thrusting. This may lead to
premature ring, piston, connecting rod and rod bearing wear
and eventual failure of these parts.

Visual Procedure

Reinstall cylinders on old pistons without rings. Hold
cylinders securely in place.

Move piston tight toward camside of engine.

Turn engine over in normal direction of travel 2 or 3
revolutions and observe piston during process.

Move piston toward driveside of engine and repeat
Step C. If misalignment exists, piston will appear closer
to cylinder wall at one point around circumference.
Condition can be corrected by bending rod in opposite
direction. Figure 1 shows an exaggerated side view.

Repeat Steps B to D for other cylinder.

Remove pistons and cylinders. Observe pistons for wear
spots on sides above top compression ring. If either side
near wristpin is worn clean while side opposite is
carboned up, then piston was not running straight and
true in cylinder bore. Piston will also generally show
diagonal wear pattern on thrust faces of skirts and
possibly signs of connecting rod to wristpin boss contact
inside piston.

Checking Pin Procedure

NOTE: S&S

rod checking pin, part 53-0002, is designed to help

perform this procedure. It may also be necessary to fabricate a
rod bending tool as illustrated in Figure 2.

Insert checking pin into wristpin hole.

Place strips of paper between checking pin and
crankcase cylinder gasket surface and apply slight
downward pressure to wristpin end of rod by rotating
flywheels.

Pull papers out slowly. Drag on papers should be equal.

Rotate flywheels in opposite direction until checking pin
contacts cylinder gasket surface again. Repeat
procedure to rod again. If drag on papers is equal, no
bending is required. If one paper is loose, use rod
bending tool to tweak rod in direction of loose paper
and recheck. See Picture 1.

Figure 1

Figure 2

⁄

22"

⁄

.510 to .520 wide slot

Picture 1

CAUTION