Before refitting the Cylinder barrel, check the connecting rod for alignment if there is any indication from inspection of the Piston that it is not quite true or there is any reason to suspect that it may have been distorted. To check the Connecting Rod for accuracy, obtain a mandrel of the same diameter as the Gudgeon pin and not less than 5-in. long Pass this through the smallend bush, set the Flywheels with the big-end a T.D.C. and verify by means of a surface gauge that the mandrel is paralle with the top machined face of the Crankcase and in line with the Crank. shaft centre line. Examine the piston bosses to make sure that the small- end eye of the rod has had sufficient side clearance from the Piston, anc has not been thrusting up against one of the bosses.
Tap the gudgeon pin into one of the piston bosses, so that it protrudes very slightly beyond the inside face of the boss. Slip the piston over the top of the connecting rod engaging the protruding end of the gudgeon pin in the small end bush which, should previously have been smeared with clean oil, and drive the gudgeon pin back into place, obtaining assistance when doing so to support the piston on the opposite side, as described in a previous section for the removal of the piston.
Note that the piston is marked " EX " on one of the flat machined surfaces on the crown. This side is fitted to the front, i.e., below the exhaust valve.
Take care not to drive the gudgeon pin too far, and thus damage the piston boss on the other side by forcing it too hard against the circlip which is fitted. When the gudgeon pin is in position fit the other circlip into its groove, making sure that it is correctly seated.
Wipe the piston clean, fit the rings into position, space them so that the slots are approximately equidistant from one another around the circumference of the piston, and smear the skirt of the piston with clean oil.
If the packing washer on top of the crankcase has been taken off or broken, fit a new one into position over the spigot at the bottom of the cylinder.
Wipe the inside of the cylinder bore with clean rag, lightly smear it with clean engine oil and proceed to slide it over the piston, compressing the piston rings in turn with the fingers so as to enter them in the cylinder, which should then slide down easily into place.
It is an advantage if help is available, as an extra pair of hands are very useful during this part of the work. See that the cylinder is fitted the correct way round, the cutaway portion of the fins being of course behind the vertical drive. As the utmost cleanliness must be observed during the foregoing operations, it is advised that the hands should be thoroughly wiped before carrying out this part of the work, as no dirt or foreign matter must be allowed to get on to the piston or cylinder bore, as this would be likely to cause damage.