M-Series Piston Installation
Cylinder Preparation
Cast Iron Sleeved Cylinders
To ensure proper ring seal, it is necessary to hone the cylinder with a rigid or brush
hone. DO NOT install a new piston without honing the cylinder to
break the glaze. Finish hone with a 280 grit. Crosshatch is necessary to ensure
proper ring seal and adequate lubrication.
If the cylinder is in good condition, simply honing the cylinder may be enough to
restore the bore to an acceptable condition. However in some cases, boring may
be necessary to insure the cylinder bore is within the tolerances outlined in the
service manual.
Plated Cylinders
Includes nickel ceramic coatings (Nikasil), chrome, Electrofusion, and boron
composite. If the plated cylinder is in good condition, honing may not be
necessary. If deglazing is necessary, DO NOT use a ball hone. Use a rigid or
brush type diamond hone. Plated cylinders cannot be bored oversize without
replating or resleeving.
Any time a cylinder is bored or honed, all ports must be chamfered. The top of the cylinder
should be deburred, and the bottom should be generously chamfered for ease of piston and
ring installation. When boring a cylinder with an exhaust bridge, the face of the bridge must
be relieved .002”-.004” to allow for bridge expansion. Without proper bridge clearance, engine
damage could occur.
IMPORTANT: After honing, the cylinder must be washed with warm soapy water to
remove all honing grit. Be sure to wash away any grit that may have traveled into the transfer
and exhaust ports during honing. The cylinder is NOT clean until you can wipe the cylinder
wall with a clean, oil dampened cloth, and it does not pick up any honing grit. Lightly oil the
cylinder bore to prevent oxidation and assist with piston installation.
Exhaust Power Valves (2-cycle engines)
When boring cylinders with exhaust power valves, the exhaust power valve must be inspected
to ensure it does not extend into the cylinder. The exhaust power valve must have
approximately .015” clearance from the cylinder bore. Without proper clearance, the
exhaust power valve could contact the piston and engine damage could occur. If
machining the exhaust power valve is necessary, remove metal only in the area that extends into the cylinder.
Piston Installation
Wiseco “M Series” pistons are designed to run at a specific piston to cylinder clearance, and
are manufactured under controlled conditions for a specific bore size. Finish hone the cylinder
to achieve the recommended piston to cylinder clearance, which can be found on the label
on the piston box.
NOTE: Additional bore clearance may be necessary for modified engines. (May include head
or cylinder work, aftermarket pipe, or ignition modifications)
Always use new gaskets for assembly. No head gasket material should extend into the
cylinder bore. When installing a piston that exceeds the OEM overbore sizes, it is recommended
that you use an over bore gasket kit. (Most models available from Wiseco)
Install the piston rings as outlined in the ring installation instructions.
IMPORTANT: Always check the rings for proper end gap.
Place a shop towel over the engine case opening to avoid dropping any components into the
engine. Install the piston with rings onto the connecting rod. The arrow on the dome MUST
point toward the exhaust side of the cylinder. Install the cylinder as outlined in the service
manual, using proper assembly methods and torque specifications.
A break in procedure is necessary for proper ring seal. Refer to the service manual for proper
break in procedures, air filter service, and oil premix ratios.
IMPORTANT – Piston pin retainers must be installed with care. Wire type retainers and
snap-ring type retainers must not be collapsed smaller than the piston pin-hole diameter
when being installed into the piston.
CAUTION - If the piston pin retainers are damaged, crimped, bent, or over-collapsed
upon installation, the piston pin retainers may fail as the result of this damage. If piston
pin retainers become damaged upon installation, it is recommended to contact Wiseco
Piston Inc. for replacement retainers.
Lubrication holes (2-cycle engines)
If the cylinder has an exhaust bridge, the piston should contain lubrication holes on the skirt
where it contacts the exhaust bridge. If the piston does not have the lubrication holes on the
skirt, follow these steps to drill the lubrication holes.
1. Install the piston and wrist pin on the connecting rod using one circlip.
2. Slide the cylinder over the piston and align it to its normal position on the crankcase.
3. Slowly turn the engine over until the bottom ring groove is at the top of the exhaust
bridge.
4. Reach through the exhaust port with a pencil, and mark a
vertical line on the piston on both sides of the exhaust skirt.
5. Remove the cylinder and piston, and drill 2 holes (.060 - .090”
diameter), .375” apart, starting .300” below the bottom ring,
and between the pencil lines. (See illustration B)
6. Remove all burrs from the lubrication holes, and clean the piston thoroughly.
