Steve Jowett www1.kingston.net/~fortierg/mainb.htm
Tappets, cam followers and pushrods
|Material:-||Cast iron grade 14 with Stellite tip|
|Material:-||Heat treated Dural tube 'B' or 'S'|
|Inlet:-||Assembled length 8.166" - 8.130" (207.416mm - 206.466mm)|
|Exhaust:-||Assembled length: 7.321" - 7.285" (186.053mm - 185.039mm)|
The following applies to the cam followers and pushrods for the Norton twin.
The cam followers are generally of good quality and last for many miles. Upon disassembly it is advisable to inspect the Stellite tip for wear and possible loosening. This is especially true if modified cams or Combat cams have been in use. The added lift can apply more stress to the followers, resulting in premature failure. I have heard of incidents where the tip has come off and made a mess of the cam and crankcase area. Also check inside the follower for the possibility of left over casting sand. I have seen it and have also read about it in a few articles.
The followers should always be kept in pairs and as such should always be replaced in pairs. Keep in mind to have the bevelled end toward the front upon re-assembly. A question was asked a while ago about the clearance for the followers in the pushrod tunnel. Although I can't find any information on this clearance, I would suspect that 0.004" - 0.010" would be acceptable. The followers being made from cast iron as well as the cylinder barrel will expand at the same rate where by giving a fairly stable clearance throughout the heat range experienced by the motor. The pushrod tunnel acts as a oil return so some clearance must be maintained, in order for the oil to get to the camshaft lobes. Upon re-assembly don't forget to tie wire the screws holding the followers. Pushrods require very little attention. The following should be checked when the pushrods are out. Inspect the tips for looseness, and check that the pushrods are straight.