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.

Loosen the clamps (7) and remove the hoses (8) and (9) from the cylinder barrels (10) and from the alternator-side crankcase cover.

The following procedure is described with the engine removed from the frame and the cylinder head removed from the engine (Sect. 9 - 4.5, Removal of the cylinder heads).

Use the tool 88765.1523 to bring the piston of the horizontal cylinder near the 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 described below.

Lift the barrel-piston assembly clear of the crankcase studs. If work is to be carried out on the piston, carefully withdraw it from the cylinder.

To remove the vertical barrel-piston assembly, bring the vertical piston to TDC and proceed as for removal of the horizontal cyl­inder barrel.

Check that the walls of the cylinder bore are perfectly smooth. Measure the cylinder bore diameter at 50 mm from the top face and determine the size class to which it belongs in accordance with the values specified in Sect. 3 - 1.1Cylinder/Piston. Re­peat measurement of the diameter at three heights A (10 mm from the upper surface), B (50 mm from the upper surface) and C (100 mm from the upper surface) and in two direction at 90° between them; check that the measurements of taper and ovality in the bore fall within the range specified in Sect. 3 - 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 piston diameter must be measured at 7.5 mm up from the bottom of the skirt and in perpendicular direction to the pin axis.

The prescribed values are given in Sect. 3 - 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.

Coupling clearance values with the piston and the connecting rod, see Sec. 3 -1.1, Cylinder/Piston.

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 segment (1st) and 0.10 mm for the others (2nd and oil scraper ring).

Insert the ring in the cylinder bore so that it is positioned 50 mm from the top face of the cylinder barrel; make sure that the ring is positioned perfectly square to the cylinder walls by checking with a gauge at several points around the ring that the top surface of the ring is exactly 50 mm from the top face of the cylinder barrel.

If new units are used, it is necessary to couple the cylinders and pistons of the same selection (see paragraph “Overhaul of the cylinder barrel/piston components” of this section).

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 recess is on the side of the exhaust port.

Using the cap 88713.1920, fit the O-rings (A) on each stud bolt and guide them into their seats in the crankcase.

Close the crankcase opening with a cloth to prevent foreign objects from falling inside and then fit the retainer ring (2) as shown in the figure.

Repeat the procedure for the other cylinder and refit the cylinder heads (Sect. 9 - 4.5, Refitting the cylinder head assemblies).

In case they have not been assembled, apply prescribed threadlocker to unions (6) and tighten them to a torque of 25 Nm (Min. 23 Nm - Max. 27 Nm) (Sect. 3 - 3, Engine torque settings).

Fit the tubes (8) and (9) and tighten clamps (7) to a torque of 2.5 Nm (Min. 2 Nm - Max. 3 Nm) (Sect. 3 - 3, Engine torque settings).