Norton Service Release Database N3/49

SERVICE RELEASE N3/49

NATURE OF RELEASE: Symptoms of Pre-Ignition MODELS AFFECTED: 1973 850 c. c. Commando Model DISTRIBUTION: Worldwide (General Distribution) EXPLANATION: Symptoms of mild pre-ignition at low engine R.P.M. on sudden throttle openings are eliminated by removal of sharp edges and corners in the combustion sphere.   ACTION: On machines reporting pre-ignition symptoms, remove the copper cylinder head gasket and, using a small flat scraper, remove and blend the sharp edges on both sides of the casket cylinder bore piercings. It is also recommended that at the same time the top corner of each cylinder bore is scraped and blended to remove any possibility of sharp edges or 'burrs'. Great care must be taken to ensure no abrasive particles whatsoever fall into the cylinder bore and lodge between the piston top land, top compression ring and cylinder wall during this operation. Check the cylinder head prior to replacement and remove any sharp spark plug ; thread 'run-out' into the combustion sphere. Finally, check the carburettor needles arc located in the central (one below top) groove as recommended in Service Release N3/48. May 1973 Norton Villiers Canada Limited