Norton 850 Commando “Stage Two” Road Racing Conversion Service Release
Download the complete PDF version using the green download button at the top right of this page for Norton Service Release N3/64 covering the 850 Commando “Stage Two” road racing conversion. Issued in April 1974, this factory technical release details the engine and induction modifications required to convert a standard 850 Commando to Stage Two racing specification.
The service release covers camshaft replacement with the 4S racing camshaft, piston crown machining, cylinder head conversion for 10.5:1 compression and full-flow porting, push rod shortening, carburettor and velocity stack changes, and exhaust system recommendations. It also provides valve clearance and ignition timing settings for both contact breaker and electronic ignition setups.
Detailed drawings show the required piston cutaway changes, cylinder head machining and port profiles, push rod modification dimensions, carburettor mounting arrangement and megaphone exhaust dimensions. The bulletin also notes the use of 36 mm Amal concentric carburettors, racing air tubes, minimum 100-octane fuel and caution against over-revving beyond 7000 rpm in top gear.
Contents Include
- Factory Norton Service Release N3/64
- 850 Commando Stage Two road racing conversion
- 4S racing camshaft specification
- Piston crown valve cutaway machining
- Cylinder head full-flow porting and 10.5:1 compression setup
- Push rod shortening dimensions
- 36 mm Amal carburettor and velocity stack guidance
- Valve clearance and ignition timing settings
- Carburettor mounting measurements and manifold notes
- Roadster muffler and megaphone exhaust recommendations
- Fuel octane and maximum rpm cautions
