Pistons and Rings

Explanation
We are aware of a condition of severe over oiling and previously some improvement has been achieved by the change of scraper ring type and more careful assembly of the scraper rings. However, a certain number of machines have still returned unsatisfactory oil consumption figures. As a result of intensive test rig and road tests, the problem has been pinpointed as a manufacturing discrepancy in the middle (tapered face) piston rings. After consultation with the ring manufacturers, a change in manufacturing techniques will prevent any reoccurence on future rings. To cope with any machines giving trouble in service, a revised form of piston ring is being made available immediately.

Action
On any machine returning an oil consumption figure heavier than 200 miles per pint, replace the middle ring on both pistons with the special ring Part No. 06-2262. It is essential to fit these rings with the word 'top' facing upwards so that proper oil control is gained. This special type of ring is identified by a chamfer on the inner diameter. We are confident that after this rectification the over oiling problem will be overcome.

(July 1970)

Explanation
Spring expander type oil control rings have been introduced on the motorcycles specified above. The piston bodies are revised to accommodate the spring expander type of ring and for this reason it is not possible to use the later rings on an earlier piston or vice versa. For spares purposes the revised pistons with rings as a pair can be used to advantage on previous Commando models. It is not considered good practice to assemble an engine using one old type and one new type piston. The part numbers of the old and new components are detailed below.

(June 1971)