SAFETY FIRST: Protective gloves and eyewear are recommended at this point.
Remove the cylinder. See the Cylinder topic for more information.
Piston Removal
Place a rag under the piston to support it and prevent any foreign objects from entering the engine.
Use the cutout provided to grasp and remove the piston pin circlip with a pair of needle nose pliers. Discard the circlip.
Hold the piston and push the piston pin out the side the circlip was removed from. A deep well socket or 3/8″ ratchet extension work well for this job.
Lift the piston from the connecting rod.
Piston Inspection
Measure the piston diameter .200 inches or 5 mm up from the bottom of the piston skirt and 90° from the piston pin hole. Compare your measurement with specification.
Piston diameter: no less than 99.80 mm or 3.929 inches
Rings
The rings should be replaced with new ones any time the cylinder is removed, there is no need to measure the old ones for wear.
Piston Installation
Special care must be taken when installing the piston rings as they are very brittle and easily broken.
Note the arrow on the piston crown. This arrow depicts the front of the piston and should point to the exhaust side of the engine.
Install the oil control expander ring in the bottom piston groove. Be sure that the ends of the expander ring butt against one another and do not overlap. Position this ring so that the opening faces the rear of the piston.
Install the bottom and top oil control rings in the same bottom piston groove on each side of the expander ring. The bottom oil control ring opening should face the front of the piston while the top ring should face the rear. Once in position move the top oil control ring to the left about 30 degrees and twist the bottom ring to the right about 30 degrees so that each ring opening is pointed slightly to the side.
Install the second ring into the middle groove. When installed properly, this ring is wider at the bottom and slightly tapers towards the top. The late model piston ring shown here features a “2N” marking that should face up- some models may only show an “N”. Pay attention that this ring is installed properly, if it is installed upside down the engine will burn oil and smoke heavily. Position the opening on this ring so that it faces the rear of the piston.
Install the top ring into the top groove. Early model KLRs have a symmetrical ring that could be installed either way – late models rings feature an “N” stamping that should face up. Position this ring so the opening is towards the front of the piston.
Lubricate the piston pin with engine oil and install the piston onto the connecting rod.
Hold the piston and push the piston pin into place.
Install a new piston pin circlip with a pair of needle nose pliers. Always install the piston pin circlip with the opening facing the 12 o’clock or 6 o’clock position.