Magneto bolt tight, but rotor still spins loose!

[feelergaugephil]

This has got me baffled!
I am fixing a GS 1000L (79) for a good friend of mine, I did the piston rings/valves etc etc, we also noticed that the 3 allen bolts had come loose behind the magneto, well, the rotor was too messed up to be fixed, anyway, I won a GS1000L 1979 rotor/starter clutch on ebay, sweet! well that's what I thought!
Here's the deal. We cranked up the GS after rebuild, 3 turns on the starter and she cranked up, we cranked her up a few more times and then we thought the starter was going out, replaced the starter and the same noise (starter just spinning) we pull off the left case and discover the 17mm bolt in the middle of the rotor was loose! I know I tightened it up, so I re tightened it and then with it TIGHT (even with impact) I can turn the rotor anti clockwise and literary undo the bolt loose, the rotor was a bitch to get off originally but now I can pull it off very easy when I remove the bolt, it appears that the rotor will not lock tight on the crank! any ideas guys, as I am baffled, I have done these jobs on GS's a bunch of times and never come across this!
HELP!
Phil.

[earlfor]

I will guess that the original starter clutch spun enough to wear the seat area down a thou or so and consequently, you can not tighten it up. Usually loctite will work if occasional slipping is the problem, but it sounds like your problem is it will not seat due to excessive clearance. I have not had need to use this solution, but a member a few years ago did use it successfully.
He cut a wrap around shim from an aluminum soda can leaving an end gap about like you would have on a piston ring. I think he fitted the shim into the starter clutch and then installed the clutch onto the shaft. If I remember, he loctited both faces of the shim.

Earl

[focus frenzy]

you can use permatex 20297 "bearing mount for worn parts"
that will glue that bugger on there good and it will fill gap to .020" or you can do the shim as recomended by Earl and use permatex 64000 high temp sleeve retainer.
it has the same strength and temp range as the first one but is thinner and does not fill as thick.

when the rotor came loose on my 1100E this past fall it chewed up the end of the crank and it didn't have a good taper to hold the rotor and I used the 64000 and so far it is doing good.

you do need to use a good brake cleaner de-greaser to get all the oil off and out and I recoment also using permatex surface prep activator #24163

[Matchless]

I had a similar problem and found that the crank tapered shaft where the rotor goes had some circular scoring with high spots. I used some 800 grit sandpaper and turned a cone then pushed the rotor on and turned it in circular motions to sand down the high spots. It shows up quite clearly when you start. I also used a bit of valve grinding paste. It took some elbow grease I must say.
Once it seemed smooth enough the fit was much better. Cleaned it up, locktighted it torqued the bolt and its still holding.

The idea behind the sandpaper inside the rotor was to retain the angle as par as possible. The grinding paste then will ensure that the final angle of fit is retained. The tapered design ensures that the full rotor surface in in contact with the full crank tapered surface to allow for the most surface resistance when torqued up.
I also locktighted the bolt

[feelergaugephil]

I had a similar problem and found that the crank tapered shaft where the rotor goes had some circular scoring with high spots. I used some 800 grit sandpaper and turned a cone then pushed the rotor on and turned it in circular motions to sand down the high spots. It shows up quite clearly when you start. I also used a bit of valve grinding paste. It took some elbow grease I must say.
Once it seemed smooth enough the fit was much better. Cleaned it up, locktighted it torqued the bolt and its still holding.

The idea behind the sandpaper inside the rotor was to retain the angle as par as possible. The grinding paste then will ensure that the final angle of fit is retained. The tapered design ensures that the full rotor surface in in contact with the full crank tapered surface to allow for the most surface resistance when torqued up.
I also locktighted the bolt

That actually sounds like a good idea......

[feelergaugephil]

I just noticed the one I bought is off a 1978 GS1000, this should fit a 79 shouldn't it!

[derwood]

Perhaps the bolt is bottoming in the hole, What if you put a thicker washer under the head of the bolt that is big enough to fit over the first part of the taper? even just as a trial to see if the rotor will bite.

[feelergaugephil]

Tried that! I can still spin the rotor anti clockwise!

[tkent02]

Interesting...

Got Pics? I'd like to see it.

[earlfor]

Should be the same.

Earl

I just noticed the one I bought is off a 1978 GS1000, this should fit a 79 shouldn't it!

[Matchless]

This is strange, but if you put a bit of mechanis blue on the inside of the rotor and turn it on the shaft you should be able to see if there is a high spot that stops it bedding completely on the taper. Otherwise your bolt may not be pulling it in, too long or something.
Good luck

[feelergaugephil]

Should the front thread of the crank butt right up to the rotor? as I can see a milemeter or 2 in there, I should have kept the old one to see what the difference was, but I threw it away!

[Matchless]

Can you post a picture, maybe it will make more sense.

[feelergaugephil]

FIXED!!!!!!!!!!!!!!!!!!!!!!!!!!!!

We managed to locate another rotor from a 79 GS1000E, bolted straight up, and tightened up correctly, cranked right up, PERFECT!
The other rotor I bought from ebay has high spots on the inside of the rotor so it would not hold or lock......
THX for the responses guys.
Phil (and Tim, to be new member soon)
We'll post pics of the running GS soon.