How does the starter actually work? I mean the mechanics of it. Our starters don't kick out the starting head like others do. Does the starter just get spun by the turning engine once the engine is running?
Nope, that's what the starter clutch behind the alternator is for. The starter can spin the engine, but the engine can't spin the starter.
On an automotive starter that "kick out the starting head" there is also a one-way roller arrangement called the "bendix" by many people that performs the same function as our starter clutches. It's quite a bit smaller than ours and on the starter itself rather than on the engine.
- Starter spins. You can hear it whirring away in the motor.
That usually means that everything fine with the starter motor themselves. Inspect the gear on the starter motor to make sure it isn't missing, have broken teeth, etc.
Yes it's rebuildable, you can replace the commuter brushes (carbon brushes) and other internal parts, but that's usually to fix a weak starter, or one that doesn't spin, not one that slips.
Could it be the starter clutch gear? Does the ares the rollers hit have to be smooth, or should it be roughed up to get a better grip?
I just looked at mine and the surface finish on the starter gear where the rollers touch, is your "standard" finish for contact points on a rotating assembly. In other words it looks just like the journals on the crankshaft, the camshaft, transmission shafts, etc.
It's a very smooth surface with a bright finish, not a mirror polish but certainly not "rough" in any way.
So, the layout of the overall system is as follows:
( from http://www.cmsnl.com/honda-cb750k-750-four-k-78-us_model7244/partslist/E++10.html )
(Click for larger view)The gear on the end of the starter engages the fine-pitched (inner) teeth on the intermediate gear #3 near the top of the image.
The coarser teeth on the intermediate gear engage with the large outer teeth on the main starter gear #6.
The starter clutch rollers (#19) rest within tapered grooves in the starter clutch body (#7) which is bolted to the back of the alternator rotor (#11). The springs and caps (#8, #9) keep the rollers pushed towards the deepest end of their grooves.
As the starter gear rolls (in a forward direction, or counterclockwise as viewed from the alternator side of the crank), the large starter clutch rollers roll in their slots, which become shallower. Thus, the rollers try to move inward toward the starter gear. This inward pressure causes the rollers to grip the starter gear, transmitting force from the gear through the rollers into the starter clutch body which is bolted firmly to the alternator rotor which is bolted to the end of the crankshaft.
Crank spins, bike starts.
When the engine fires, and the speed of the crankshaft exceeds the speed of the starter gear, the clutch rollers roll in the opposite direction in their slots, back to the deep ends. This releases the griping pressure and thus the starter system disengages from teh crank.
So, there are several places where slipping could occur that would result in the starter spinning but not turning the crank:
between the starter and the intermediate gear,
between the intermediate gear and the starter gear,
between the starter gear and the starter clutch,
between the starter clutch and the alternator rotor (unlikely!)
between the alternator rotor and the crank (unlikely!)
When you rebuilt the starter clutch, you should have been able to test it by trying to turn the starter gear on the crank. It should spin freely in one direction but not at all in the opposite direction. Was this the case?
Next, are you sure you re-installed the intermediate gear properly?
Third, have you had the starter out of the motor? How did it look?
With the starter out of the motor, you should be able to look into the hole in the starter cavity and see the intermediate gear. Reach in and try to turn it. It should spin in one direction but not the other. If it spins in both directions, the problem is in the gearing or the clutch and not the starter.
I suppose that in theory, the starter clutch housing could sheer of the back of the alternator rotor, or the rotor itself could be loose and spinning on it's taper on the crank, but you'd likely have noticed either one of these problems and they don't seem to be common failures at all (ie I've never seen them).
mystic_1
