Below I documented the fix for the slipping 4th starter gear. I want to add the original poster/author is below. All I did was test and post pictures to what he is writing about. I applied this fix years ago to a kick starter spring the same way with success.
The reason why the starter slips and spins out because the spring has lost it's tension or was never set properly. This is what I found.
The spring has to be at 6 pounds. I found when it gets to 4 pounds it slips. I tested this on 3 other bikes. They were all at 4 pounds that slipped, new aftermarket-used aftermarket OEM or otherwise. Just takes 2 pounds difference.
This is what happens to the gear when the spring is at 4 pounds pressure.
This is a fish scale I bought at Walmart for $15.00. I'll keep it and use it to adjust the steering head.
Here is the factory spring tension rate
I have gotten two of Mikes stater kits for 2 of my bikes and one worked fine and the other just spun. This is what I've found on the adjustment. You can only squeeze the spring in a vise. No matter how hard you squeeze you only achieve 6 pounds. So if you don't have a scale you will be in spec. Just don't over squeeze on the vise and disform the spring.
Here is what I've also found. On the left is Mikes spring. Notice the flat sides to fit the new gear. To the right is a OEM NOS spring, it's fatter-just not grinded flat. When I put a NOS spring on Mikes gear you only get 4 pounds. If you squeeze the spring you get 8 pounds so that is the best set up. *Note* if you put a OEM spring on a OEM gear you will only get 4 pounds, the spring has to be bent in a vise.
You really can't bend it on the bike and not take it apart this this.
OEM part #
Below is a post from the author with his fix I just documented and tested. This will fix the dreaded starter problem. You could probably just remove the slipping gear and squeeze the spring and you would be fine.
#Electric starter problems on the XS650 are very common, and almost always due
to a non-functioning #4 gear, the one that slides down the bendix helix and
engages the ring gear on the flywheel. Symptoms are a starter that does not
engage, a starter that just grinds ineffectually, or a starter that kicks out if the
engine does not start immediately. The usual remedy is to replace the gear
complete with it’s spring clip, but there is an easy way to fix erratic and non
functioning starters without changing the #4 gear, even if the gear is showing
signs of severe wear.
When people remove the offending gear it is often badly worn, and they
assume that is the reason the starter does not work. But exactly the converse is
true.
IT IS NOT A CASE OF THE STARTER NOT ENGAGING BECAUSE OF A
WORN #4 GEAR. THE #4 GEAR ONLY WEARS BECAUSE THE STARTER IS
NOT ENGAGING.
One will find in removing non-functioning #4 gears from an XS650 that there is
still lots of tooth left. Now the bendix on a car will continue to engage till the
teeth are completely snapped off, and even then will turn the engine jerkily.
One usually changes them to avoid damage to the ring gear on the flywheel,
rather than because they won't engage. It’s not the worn teeth on the #4 gear
that prevents engagement. The reason the starter does not engage is because
of the spring clip on the #4 gear losing it's tension. The manual calls for about
5 lbs tension required to rotate the clip in it’s groove on the gear. The tension
found on the new ones can be up at about 8 lbs. You will invariably find that
the tension required to move the clip on non-functioning starter gears will be
down to about 2 lbs or less. This can be measured using a fishing scale.
What happens is this.
Because the # 4 gear is light and does not have enough
inertia (resistance to being rotated from a state of rest), Yamaha designed in the
spring clip to increase the inertia. This restrains the gear from turning on the
bendix when the bendix shaft is initially rotated by the starter motor. So, as the
bendix rotates, the helix on the bendix shaft forces the gear down the shaft and
into engagement, because the gear will slide before it will turn. Once it gets to
the end of the bendix, by which time it is fully engaged with the flywheel ring
gear, it has no option but to turn, it has nowhere further to slide. When the
spring tension in the clip is too weak, there is not enough restraint, so instead
of the gear resisting turning, it just spins with the bendix shaft, does not move
down the shaft fully, and is not forced into engagement. It goes down just far
enough to grind off it's teeth against the flywheel ring gear.
All that is necessary to get a starter gear working, no matter how worn the teeth,
is to bend the clip so it gets back to a minimum of 5 lbs required to move the
clip.
All that is needed to do is drain the oil, remove the kickstart lever, brake lever,
foot rest, and disconnect the tach drive cable at the side cover. Then remove the
right hand side cover. The best way is then to remove the clutch basket and
dismount the #4gear from the bike. I haven’t yet tried to do this fix with the
clutch still mounted on the bike and the #4 gear in place, but this may well be
possible. I am pretty sure that on the newer units where the loop of the spring
clip bears against the floor of engine case the that the loop will be visible just
under the forward lower edge of the clutch assembly, and you will be able to
reach in and do the following without further disassembly. On the older units
with the clip with the skinny loop inside the recess in the crankcase, the clutch
will definitely have to be removed and the gear dismounted. In any case, either
way, just use a heavy pliers, like a linesman's pliers, or a Visegrip, to squeeze t
he loop of the clip closed so it bends a little and the clip then grips the gear
tighter. If you do remove the gear from the bike, lever the clip off the gear
using a screwdriver, squeeze the loop of the clip in a vise, and remount it on
the gear. Check the tension with a fishing scale, if it is less that 5 lbs squeeze
the loop a little more.
You can test it immediately, even before remounting the clutch. Pull the spark
leads so the oil-empty engine does not start, and hit the starter button. I bet your
starter will now work, no matter what the wear is on the #4 gear's teeth.
Farrell
