Motorcycle Repair: Cam sprocket, advance mechanism, spark advance

Question
Hi Bill, thanks for your advice last time, everything worked out fine.  I've installed new pistons and I've got the head on my "63 CB 77 superhawk after a valve grind, the cam is apart in 3 pieces and I've noticed the rivets are a little loose ( 19,000 KM ) and the sprocket is moving slightly on the backing plate, the advance arms are also a little sloppy as well.  It seems to me that if the rivets were re-peened everything would be as it was but I have seem some that have been welded, what's the correct way to fix this problem.  Also I've heard mention of some neoprene in there somewhere perhaps to keep the noise down but I don't see any evidence of that and one last thing.... there is some slop where the advance springs attach to the  arms and I'm able to move the arms slightly before it has any effect on the advance mechanism, the springs are tightly wound and don't appear  stretched. Is this normal?  I've heard of some people getting in there with some needlenose and bending out the slack in the springs.  thanks for your time with these longwinded questions.

Answer
Kevin, you do have to address the loose sprocket issue, either with some TIG welding at the corners of the sprocket and center sections or replace the unit completely. There are at least three spline configurations, so you have to match the cams to the sprocket spline sets. Trying to peen the rivets again is not a good ideal

As far as the weights go, you will find some slop in the tongue of the spark advancer shaft, where it engages the center of the sprocket. The weights to get loose on the pivots and the springs stretch, allowing for some of the slack to become initial spark advance motion when the engine is running, even at idle speeds.

There was rubber bonded to the ends of the weights where they contact the inner portion of the advancer holes. IF the rubber is gone, then the weights will make some noise as they contact the inner edge of the holes and that will also cause extra spark advance because the weights are going to travel further than normal. I do bend the ends of the springs down to help reduce the unnecessary advance weight movement at idle, but that is not always successful. Sometimes, you just have to go find new parts or good used ones to replace the worn-out items that you find inside.

I have full restoration guides on CD for all 250-305 models.

Bill Silver
www.vintagehonda.com