Bold reference numbers in this section identify parts not shown in the figures alongside the text, but which can be found in the exploded view diagram.

Use service tool no. 88700.5644 to bring the piston (9) of the horizontal cylinder (8) close to TDC.

If necessary, rock the cylinder slightly using both hands or tap its base gently with a rubber mallet. Continue to lift the cylinder until you can access the gudgeon pin (3).

Since insertion of piston in the barrel is a difficult operation to perform at the time of reassembly, remove the piston together with the barrel as an assembly as described below.

Close the opening in the engine crankcase with a rag or soft paper to prevent foreign material or solid combustion residue from falling in.

Check that the walls of the cylinder bore are perfectly smooth. Measure the cylinder bore diameter (D) at three different heights and in two directions offset by 90°, thereby determining the assembly clearance, taper, and ovality (see specified values in Section C 1.1, Cylinder/Piston).

In the event of damage or excessive wear the barrel must be renewed as it has a silicon carbide coating (which provides the cylinder walls with excellent anti-friction and anti-wear properties) and therefore cannot be rebored.

The cylinders are marked by a letter (punched into the specific surface on the cylinder side) showing the class to which they belong.

For the values, refer to Section C 1.1, Cylinder/Piston.

Gudgeon pins must be perfectly smooth without signs of scoring, steps, or blueing due to overheating. The well-lubricated gudgeon pin must slide smoothly inside the piston without stiffness.

The assembly clearance with the piston at the time of installation must be 0.002 to 0.008 mm.

The maximum permissible wear limit is 0.035 mm.

The piston rings must not show any signs of scuffing or scoring. Replacement pistons are supplied complete with piston rings and gudgeon pin.

The maximum permissible wear limit is 0.15 mm for the top compression ring (1st) and 0.10 mm for the others (2nd and oil control ring).

It is essential that the measurement be performed with the piston ring (A) positioned perfectly square in the cylinder. For this reason, the piston (9) should be inserted in the cylinder without piston rings fitted and then place the piston ring to be checked on top of the piston.

Top and second piston ring (nominal): 0.20 to 0.40 mm.

Wear limit: 0.80 mm.

Oil control ring (nominal): 0.30 to 0.60 mm.

Wear limit: 1.0 mm.

The letter indicating the cylinder size class is stamped on the cylinder-head mating face; the piston size class letter is stamped on the crown in between the two recesses.

If the pistons have been separated from their cylinders, before reassembling these components, position the piston ring gaps at 120° from one another (the markings must always face the piston crown).

Use a universal tool to carefully insert the piston into the cylinder (first lubricate the inside of the cylinder with engine oil). Position the cylinder with the smallest valve pockets facing the exhaust port.

the exact configuration of the bead of liquid gasket varies according to whether the gasket is for the (6) for the vertical cylinder (V) and the horizontal cylinder (O). The illustrations below the the various configurations:

Using service tool no. 88700.5644, bring the small end of the connecting rod up to near TDC. Fit the piston–cylinder assembly on the crankcase studs.

Push the connecting rod small end into the piston close to the gudgeon pin (3) bore. Lubricate and insert the gudgeon pin. The gudgeon pin must slide smoothly in the connecting rod small end bush and in the piston (9).

Stuff the crankcase opening with a cloth to prevent foreign objects from falling inside and then fit the circlip (2) using service tool 88713.2270.

Locate the locating dowel (7), head gasket (11) and centring bushes (10).