Cylinders, Pistons and Piston Rings Inspection

Cylinders, Pistons and Piston Rings Inspection

NOTE: Before the following inspection, clean carbon from piston head and ring grooves, using a suitable tool.

Cylinders
^ Inspect cylinder walls for scratches, roughness, or ridges which indicate excessive wear. If cylinder bore is very rough or deeply scratched, or ridged, rebore cylinder and use over size piston.
^ Using a cylinder gauge, measure cylinder bore in thrust and axial directions at 2 positions (1, 2) as shown in figure. If any of the following condition is noted, rebore cylinder.
^ Cylinder bore via. exceeds limit.
^ Difference of measurements at 2 positions exceeds taper limit.
^ Difference between thrust and axial measurements exceeds out-of-round limit.
^ Cylinder bore
Standard: 88.000 - 88.020 mm (3.4646 - 3.4653 in.)
Limit: 88.050 mm (3.4665 in.)
Taper and out-of-round
Limit: 0.10 mm (0.004 in.)

NOTE: If any one of six cylinders has to be rebored, rebore all six to the same oversize. This is necessary for the sake of uniformity and balance.








Pistons
^ Inspect piston for faults, cracks or other damages. Damaged or faulty piston should be replaced.
^ Piston diameter: As shown in figure, piston diameter should be measured at a position 26.5 mm (1.04 in.) ("a") from piston skirt end in the direction perpendicular to piston pin.
Piston diameter
Standard: 87.970 - 87.990 mm (3.4634 - 3.4641 in.)
Oversize (0.50 mm): 88.470 - 88.490 mm (3.4831 3.4838 in.)








^ Piston clearance:
Measure cylinder bore diameter and piston diameter to find their difference which is piston clearance. Piston clearance should be within specification as given below. If it is out of specification, rebore cylinder and use oversize piston.
Piston-to-cylinder clearance
0.02 - 0.04 mm (0.0008 - 0.0015 in.)

NOTE:
Cylinder bore diameter should be measured in 2 places 90 degrees apart.








^ Ring groove clearance:
Before checking, piston grooves must be clean, dry and free of carbon. Fit new piston ring (1) into piston groove, and measure clearance between ring and ring land by using thickness gauge (2). If clearance is out of specification, replace piston.
Ring groove clearance
Top: 0.03 - 0.07 mm (0.0012 - 0.0027 in.)
2nd: 0.02 - 0.06 mm (0.0008 - 0.0023 in.)





Piston Rings
To measure end gap, insert piston ring into cylinder bore and then measure the gap by using thickness gauge. If measure gap is out of specification, replace ring.

NOTE:
Clean carbon and any other dirt from top of cylinder bore before inserting piston ring.

Piston ring end gap