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Starter just spins


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1982 Katana 1100. I don’t know the history of this engine, but I’ve just put a battery on the partly rebuilt bike to start to check the wiring. I pressed the starter button and the startermotor spun without showing any attempt to turn the engine over. I clicked it a half dozen times and each time I can hear the starter spinning but not contacting anything. The final time all I got was the solenoid clicking. This is using a fully charged battery. If I remove the left engine cover will I see the starter sprag system?

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OK, I’ve opened it up. Removed the outer cover that holds the stator. Inside there is the starter drive gear, twin idler gear on a shaft and then the main drive gear inboard of the rotor. 

firstly, the large drive gear can revolve separately from the rotor in one direction, as I would expect the sprag drive to do. And then won’t in the other which would allow the starter to drive it all. 
 

why is the whole rotor unit able to revolve separately from the crankshaft itself? I was under the impression the rotor was tight on the crank by way of a taper, according to the Haynes manual (sorry, it’s all I could get my hands on) 

I was expecting the rotor to be solid on the crank, and then perhaps the 3 bolts holding the sprag unit onto it to be faulty 

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Thanks guys. Typically, it was bleedin’ obvious innit, as soon as I put a whizzy gun on the crankshaft nut. First of all it was f-tight as to be expected, in fact I had to go out and buy a new impact wrench just now before attempting removal. 400nm was no match for that nut. It spun off, followed by the rotor immediately afterwards. Oh dear, that lovely smooth taper is no more, it’s not a nice state. Now where’s the grinding paste? I haven’t used that stuff for 30+ years. 

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not at all, I’m pleased you didn’t go OH SH*T NO!
 

I just hope I don’t lap it back too far........ :S

oh, and the fact that the nut was tight, and the rotor was able to spin, it could be I will need to add a spacer/shim to the nut side to get it to do up further. 

Edited by Malone
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Nah... its fixable. Maybe even add a key way or such?

 People have been know to just weld the rotor to the taper as a quick fixer up... it wont last long. 

 

Lapping and grinding both the rotor and the taper is the correct way. Adding a shim will help too (y)

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It’s fixed. Some nice oily emery tape helped to remove the nasty high spots, and a finger wrapped with the same tape gingerly inserted into the rotor itself did the same. So, I reassembled it all and whizzed it back up - sorted. :tu

just waiting for a new gasket to arrive and it can go back together again. 

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