Motorcycle Repair: c65, horizontal singles, drive sprocket

Question
Hi Bill,

 I have a honda cub 65 and am wondering why I'm only getting 3volt output when it is running.  Thinking it maybe the lighting coil.  Is this one different than the primary ignition coil.  They look similar.  Also wondering if the piston and rings can be replaced without total dismantle,  that is without removing the crankshaft.

                     Thanks .........Ron

Answer
Ron, in case you don't have the wiring diagram, go here:
http://www.oldmanhonda.com/MC/WiringDiagrams/MCwiring.php#class
There are a couple versions listed there, so I am not sure which one will work for you. If you have a rectifier with more than 2 connections, probably the rectifier has failed.

3v isn't going to keep the 6v battery up on its feet, obviously. There are several taps off of the lighting coil and to really take a close look at it, you will have to buy a flywheel puller and remove the flywheel to access all the components, underneath. You can check the AC voltage legs coming off the stator and see if you are getting power off of all of them. If you are, then probably the rectifier is toast or wires/wiring connections are bad. If you have a dead leg, then you will have to replace the lighting coil. The primary coil for the ignition is separate and completely different from the lighting coil setup.

The engine is just like the other 50-65-70cc horizontal singles, in that it is a simple OHC design and the top end can be removed in the frame w/o having to tear it out and split the cases. If you have to change the camchain, then again the flywheel will have to be pulled to access the end of the crankshaft, so you can feed the chain over the end and reset it on the crankshaft's drive sprocket.

Bill Silver