(3) Replacing pistons Replace the piston with a new one if the measure- ment exceeds the service limit. Where any pistons have to be replaced, the variance in weight among the pistons must not exceed the limit. It is recommended that cylinder number be stamped on a piston selected to be used in a particular cy- linder for convenience. When the cylinder sleeves are bored to the oversize, pistons and piston rings of the same oversize should be used. There are three oversizes for pistons and piston rings, namely, +0.25 mm (0.00984 in.), +0.50 mm (0.01969 in.) and 0.75 mm (0.0295 in.). The variance in weight among the pistons per engine should be ±5 grams (±0.18 oz), max.
Front of engine t Pilton _ight Piston weight marking (4) Piston riD& gaps Check the ring gap with a thickness gauge by placing the ring in a new cylinder sleeve, and pushing the pistOll true and square in the bore. Piston ring Gap Checking piston ring gap Specifications Unit: mm (in.) (5) Piston ring grooves Insert the compreuion and oil rings of known thicknesses into the grooves, and measure the side clearance with a straightedge and thickness gauge@.
Measuring piston ring groove Specifications Unit· mm (in ) -23 - Item Standard Service limit Piston ring gap 0.30 ~0.50 (0.0118 ~ 0.0197) 1.5 (0.059) Item Standard Repair limit Fit in ring grooves No.1 compression ring 0.050 ~ 0.085 (0.00197 ~ 0.00335 0.20 (0.0079) No.2 compression ring 0.025 ~ 0.060 (0.00098 ~ 0.00236) 0.15 (0.0059) Oil ring