Starter Motor Internal Gear Slipping?

I'm out of ideas on this one. I recently (as in this weekend) rebuilt the starter on my '76 KZ750 (twin, 4cyc.). New bearings, new brushes, brush holder, etc. Everything was replaced except the housing, armature, output shaft, planetary pinions, internal gear, and internal gear holder.

Previous to the rebuild, the starter would crank a couple of times and then stop. Now it just whines (but doesn't stop -though I never crank it for more than 4 seconds at a time).

When the starter was off the bike in it's rebuilt condition, I could hook it up to a similar current and get it to spin, but I felt like the internal gear was slipping a ton. When I first opened it up, the internal gear never moved as far as I could see, and the planetary pinions did their thing and turned the shaft. While putting it back together I noticed that the internal gear spun freely. Not knowing TOO much about the starter, I assumed it was supposed to do this to create a different (lower, slower) turning motion than if it were fixed.

The starter solenoid/relay is also broken (one is coming to me from ebay any day now), so I have to use a screwdriver to jump and bypass it. This happened the same time I decided it was time to rebuild the starter - coincidence?

I did notice that there was no 'T' key where one was supposed to be according to the manual. So here are my questions:

1. What is the prupose of the T key? To keep the internal gear from spinning?

2. Is the internal gear supposed to spin? It sits in the internal gear holder and as far as I could tell, the holder doesn't keep it from spinning.

3. In the troubleshooting section of the shop manual, it lists internal gear slipping as a reason for the motor winding but not cranking the engine (along with bad starter clutch and loose dyno rotor bolt)

I feel like the internal gear slippage is the problem, as it just causes everything to spin in the starter housing but not really spin the output shaft, but I don't know how to remedy it.

Sorry this is so long, but I wanted to provide as much info as possible. Thanks guys!

I'm attaching a diagram of the starter - the 'T' key is #22

I am not an expert on these starters, but in any planetary gear system, either the ring gear or the planetary gears must be locked in order for power to be transmitted. Clearly, there is no locking mechanism for the planetary gears in this starter, so that leaves the ring gear, which makes sense since that is how reduction occurs. I'd bet that the T-key locks the internal gear and its holder together.

I suppose out of desperation one could apply a couple of tubes of JB Weld and some 3- inch wood screws :evil:

I had a loose dyno rotor one time. The starter would spin but because the rotor was loose the gears would not mesh. It took a while to track it down, once fixed I have had no problems.

I saw a tray of keys at the local hardware store- but I can't find any specs as to what size I need for this starter. I may just buy a bunch (they are cheap), and trial and error them. Or just take the starter with me.

Blink, Not familiar with your' starter, but at a glance is very similar to Yamaha Virago 750/920 configuration which was infamous for failure to spin motor. Yamaha's fix was to shim the internal gear (17 in your illustration) (among other fixes) until it no longer slipped. personal experiance is/was that this was a iffy fix and usually temporary. In desperation I effected a diffrent approche. It requires some pretty close measurements, but in essence, one drills a hole thru starter housing (starter assembled) and midway into internal gear. and drives an interfearance fit pin into hole. ( I use old 2 stroke wrist pin bearing rollers, as they are hardened, and yet small enough to shear without damaging housing.) PS. the reason the internal drive gear was never solidly fixed, was to prevent starter damage in the event of severe back-fire. Typical disclaimers apply.hope this helps G

Ahhh. This sounds like what I need to do. I have fixed it a 'little' - some grease had gotten onto where it shouldn't have making it super easy for the internal gear to spin. It'll roll the engine over now a couple of times, but then spin and whine - Which leads me to wonder - IS the starter acting like it's supposed to and letting the internal gear spin because something else is going on? You know what I mean? Maybe the starter is fine but something else is keeping the engine from rolling over.

So you have a pin holding the gear in place? When you said 'shear without damaging the housing' did you mean in case the torque was so bad that the internal gear needed to slip it would shear that pin cleanly and spin? I think I'm going to try first to add a few more washers (19 in the picture - 'thrust' washers) to compress that gear to the end plate (13)..

Still how can I know if the starter is fine, and is slipping because something else is going on? If it happens to turn over 4 or more times the engine fires up fine.

Blink, pretty close, but I doubt the starter makes enough torque to damage its mechanical componants. much more likely if engine were seized, starter would cook electrical componants. hope shimming works for you. luck g

Ahhh. I'm slow. I get it now - you used one of the rollers off of the bearing like the one I attached? This I can do