Instruction manual

Remove

One gudgeon pin circlip. It is immaterial which circlip is removed. Use special pliers

included in tool kit.

Gudgeon pin by pushing it out of piston.

Take away piston.

NOTE—The gudgeon is an easy sliding fit in both piston and connecting rod small-end

bush.

Rings may be removed from a piston by " peeling off" with a knife, or by

introducing behind the rings three pieces of thin steel spaced at 120° from each

other and then sliding off the rings. (Do not scratch the piston.)

TO REPLACE THE PlSTON AND CYLINDER BARREL

All parts must be clean.

Place rings on piston. (Scraper first then the two compression.) (On 500 c.c. models the

top compression ring is chromium plated and is marked on one edge " top " for refitting.)

Smear gudgeon pin with engine oil.

Refit piston by :

Introduce piston over connecting rod, so that slit in piston faces to the front of the

machine.

Introduce gudgeon pin in piston and pass it through connecting rod small-end bush and

centralise it.

Re-fit circlips. (Use special pliers). Use rotary action when bedding circlips in their

grooves and make sure each circlip lies snugly in its groove. This is essential otherwise

considerable damage will result.

Re-fit cylinder barrel by :

Take new cylinder base washer. Coat one side with liquid jointing compound and

apply it to cylinder base. Ensure jointing does not choke any of the cylinder base oil

holes.

Smear cylinder bore and piston with engine oil.

Space piston rings so that the gaps are evenly spaced at 120° to each other.

Remove rag from crankcase throat.

Fit barrel over piston. Ensure each piston ring is fully compressed into its groove,

in turn, as the barrel passes over it.

Replace cylinder barrel holding down nuts, screwing each down, in turn, bit by bit, till

all are fully home.

CAM CONTOUR

On the flanks of the cams are quietening curves which are very slight inclines from the

base circles to the feet of the humps.

Therefore, it is necessary to ensure the tappet ends are on the base circles when checking

valve clearances and valve timing.

It is for this reason valve clearances must be checked when the piston is at the top of its

compression stroke, at which position both tappets are well clear of the quietening

curves.