81 750CWon't charge

[scottn3n]

I have an 81 CB750C and it won't charge.  The voltage regulator has been replaced, the alternator brushes are in good shape and the wiring has been checked between the regulator & alternator (with an ohm meter).  We  also checked the wiring between the battery & regulator.  The terminals were cleaned & still no luck.  Ground is good.  The only thing I can think of is the thingy that holds the starter relay (all of the wiring plugs into this).  Do these go bad?  What's in there?  Any other ideas, please?  Right now it's running off the battery, and everything else works.  I know how to bypass the voltage regulator on a car to check the alternator, but this has 3 wires to the alternator field windings instead of 1.  Is there a way to bypass the regulator to the alternator to check it without damage?  Do you just connect all 3 field wires to the battery?  This should make the alternator work 100%.

Thank you.

[BullMagnum]

Did you ever figure out your problem with the charging?
I am having the same trouble with my 1980 CB750K.

[magnum56]

Posted this on BullMagnums question too - just in case it helps...

This might be a little obscure, but I had a similar issue years ago with my 74 CB750.  Tested everything "by the book" and I could not find the problem.

Eventually, while tinkering, I noticed the rotor itself was turning (slipping) on the end of the crankshaft.

The rotor on mine was held in place on the tappered end of the crankshaft by a bolt into the end of the crank.  There was no key or keyway utilized to keep the rotor from slipping if the bolt loosens some.

Remember that the rotor makes and breaks the magnetic field created by the interaction between the stator and field coil.  If you can turn the rotor by hand (without the engin "turning over as well) the rotor is loose and when the magnetic field is created, the rotor will slip on the end of the crank.

Re-torquing the bolt on the end of the crankshaft was all mine needed to correct the issue.  

Good luck ...