Norton Service Release Database N28

SERVICE RELEASE N28

NATURE OF RELEASE: Cam chain tension MODELS AFFECTED: Commando with cam driven contact breaker DISTRIBUTION: Worldwide (for general distribution) EXPLANATION: It is found that slackness of the cam chain can result in snatch, jarring shocks being delivered to the contact breaker and auto advance mechanism. This causes premature wear on these parts. i/e specify that the chain tension should be checked at 5000 mile intervals but, naturally, any obvious slackness evidenced by noise in this area should be taken up, irrespective of milage. Adjust the cam change tensionto between 1/8" and 3/16" slack (that is, up to down movement) on the top run of the chain. To do this necessitates removal of the contact breaker and auto advance mechanism (use the withdrawal bolt 06-0934 for the auto advance cam). Next take off the timing cover, and the cam chain and slipper tensioner are exposed. The oilway exposed by removal of the cover must be blocked by one of the tining cover screws (see owners handbook) to prevent the loss of oil. Note that chain tension can only be adjusted correctly if there is no play in the intermediate spindle. To check the chain tension, remove the sparking plugs so that the engine will turn easily and use a 9/16" Whit. socket or ring spanner on the camshaft sprocket nut and turn slowly anti - clockwise so that the lower run of the chain will be kept tight on the slipper and a true check of the tension can be made on the top run. In this way the spanner will control the alternating load of the valve springs on the camshaft and it will be easy to find any tight spot to which the tension should be adjusted as described. To increase chain tension, slaclten the two nuts securing the slipper and lift it a little at a time, checking at each stage after nipping up the nuts whether the tension is correct. When the correct tension is achieved secure the slipper nuts to 1801b. in (151b. ft). It is most important when refitting the timing cover to use the camshaft oil seal guide 06 - 1359 to avoid damage to the seal in the timing cover.   December 1970 Norton Villiers Canada Limited