Piston: Service and Repair

PISTONS
Pistons are machined to two different weight specifications and matched to rods based on weight. All piston and rod assemblies weigh the same, to maintain engine balance.

CYLINDER BORE AND PISTON SPECIFICATION CHART:

Figure 7-Check Gap On Piston Rings:

FITTING PISTONS
Piston and cylinder wall must be clean and dry. Piston diameter should be measured 90 degrees to piston pin at size location shown in. Cylinder bores should be measured halfway down the cylinder bore and transverse to the engine crankshaft center line. Pistons and cylinder bores should be measured at normal room temperature, 70° F (21° C).

PISTON PINS
The piston pin is full floating and is held in place by lock rings. Pistons and rods are weight matched for balance. Do Not switch pistons with other rods. Piston and Rods are serviced as an assembly for balance.

Figure 6-Piston Measurements:

FITTING PISTON RINGS
1. Wipe cylinder bore clean. Insert ring and push down with piston to ensure it is square in bore. The ring gap measurement must be made with the ring positioning at least 12 mm (0.50 inch) from bottom of cylinder bore. Check gap with feeler gauge.

PISTON RING SPECIFICATION CHART:

Figure 8 Measuring Piston Ring Side Clearance:

2. Check piston ring to groove clearance.

Figure 9 Piston Ring - Installation:

PISTON RINGS INSTALLATION
1. The No. 1 and No. 2 piston rings have a different cross section. Insure that the No. 2 ring is installed with manufacturers I.D. mark (dot) facing up, towards top of the piston.

CAUTION: Install piston rings in the following order:

2. Oil ring expander.
3. Upper oil ring side rail.
4. Lower oil ring side rail.
5. No. 2 Intermediate piston ring.
6. No. 1 Upper piston ring.

Figure 10 Side Rail - Installation:

7. Install the side rail by placing one end between the piston ring groove and the expander. Hold end firmly and press down the portion to be installed until side rail is in position. Do not use a piston ring expander during this step.
8. Install upper side rail first and then the lower side rail.

Figure 11-Upper And Intermediate Rings-Installation:

9. Install No. 2 piston ring and then No. 1 piston ring.

Figure 13-Checking Connecting Rod Bearing Clearance-Typical:

10. Position piston ring end gaps as shown in.
11. Position oil ring expander gap at least 45° from the side rail gaps but not on the piston pin center or on the thrust direction. Staggering ring gap is important for oil control.