Rotor keeps spinning loose

[berty]

1170 et . Hi all , yep as per title - rotor keeps spinning loose . Not down to hard starting - as Efe starter and cog fitted . Starts on half a crank everytime . 

Even after crank end nut tight as fuck and nice unworn rotor fitted . 

Keyway seems unlikely as a cure - very tricky . spot weld rotor onto crank would work but bit drastic me thinks . 

Any suggestions ? 

Crank recently rebuilt - so not ready to throw it away just yet .

[Jonboy]

I would try lapping the rotor onto the taper if it were me. Wouldnt take much of a mark or dig or ding on either the rotor or the taper to stop it sitting correctly, problem too with it spinning means there may also be some marking caused by that action.  

[teltwosheds]

When reasembling give the taper and seat a good squirt with carb cleaner and dry thorourly thoourely properly 

[berty]

4 hours ago, Jonboy said:

I would try lapping the rotor onto the taper if it were me. Wouldnt take much of a mark or dig or ding on either the rotor or the taper to stop it sitting correctly, problem too with it spinning means there may also be some marking caused by that action.  

Yep got a few marks going on !! 

[bluedog59]

Clean the crank end and rotor taper with contact cleaner then lap the rotor on using fine grinding paste until you get a good fit.

Make sure you clean ever speck of paste off afterwards...... then clean it again.

 

[Gixer1460]

I second the grinding paste option - get both surfaces nice and uniform grey and matt finish. Then windy gun the crap out of the bolt. A more drastic solution is use diamond dust impregnated grease used by Ford to secure non keyed cam wheels to camshafts - the diamond dust locks them real tight!

[berty]

1 hour ago, Gixer1460 said:

I second the grinding paste option - get both surfaces nice and uniform grey and matt finish. Then windy gun the crap out of the bolt. A more drastic solution is use diamond dust impregnated grease used by Ford to secure non keyed cam wheels to camshafts - the diamond dust locks them real tight!

Interesting - diamond dust grease. Must admit - have never heard of that . 

[johnr]

is it the right rotor? different gsx cranks had slightly different tapers, if your rotor has a different taper to your crank it will only have a tiny contact point to the crank. try getting some valve grinding paste and lapping it onto the crank, then see how good the contact area is.

 

[Nigkat]

Just a word of caution, if you lap it too much you can reduce the clearance for the starter clutch and it will lock up once the rotor nut is fully tightened.

[johnr]

i dont think it will take a lot of lapping to establish if it has a good contact area onto the taper or if its just a tiny sliver.

 

[berty]

35 minutes ago, Nigkat said:

Just a word of caution, if you lap it too much you can reduce the clearance for the starter clutch and it will lock up once the rotor nut is fully tightened.

This is my main concern with lapping. 

Good to get some views coming back .

[coombehouse]

You could try using Engineers Blue. Its a blue dyed grease stuff. Put a very thin smear on the crank taper (thin as so you can barely see it) & then put the rotor on & turn it slightly. When you take the rotor off the contact point will not have any blue on it. You use the same stuff for checking valve seats after cutting. Get it from engineering supplies or Eblag.

[Gammaboy]

1 hour ago, berty said:

This is my main concern with lapping. 

 

That's a lot of lapping required to make it nip up!

[Jonboy]

I believe this & the katana motor & the EZ had 25mm dia with a 1:5 taper. The 83 on ESD with the half fairing & the 1150 motors had 29mm with a 1:7 taper. I think this sorts out the question of taper size, it would be obviously wrong. As for lapping, the amount of material you removed would be similar to lapping valves (unless you have some major digs or depressions). So, if you unsure maybe try engineers blue first to confirm where your contact points are, and probably more pertinent , where it isnt contacting and then take action from there by lapping.

[Gixer1460]

10 hours ago, coombehouse said:

You could try using Engineers Blue. Its a blue dyed grease stuff. Put a very thin smear on the crank taper (thin as so you can barely see it) & then put the rotor on & turn it slightly. When you take the rotor off the contact point will not have any blue on it. You use the same stuff for checking valve seats after cutting. Get it from engineering supplies or Eblag.

Or Sharpies 'Magic Markers' / similar felt tip marker pens - work just the same. Who knew WH Smiths did engineering supplies!

[Nigkat]

21 hours ago, Gammaboy said:

That's a lot of lapping required to make it nip up!

been there done that.

[berty]

Have a plan now - all will be revealed !!

[Gpz1100_Convert]

On 14/04/2016 at 11:42 PM, coombehouse said:

You could try using Engineers Blue. Its a blue dyed grease stuff. Put a very thin smear on the crank taper (thin as so you can barely see it) & then put the rotor on & turn it slightly. When you take the rotor off the contact point will not have any blue on it. You use the same stuff for checking valve seats after cutting. Get it from engineering supplies or Eblag.

cheap equivalent is a permanent marker pen or a whiteboard pen. Both work the same and save some faffing about. I nick them off my old lady....

 

Mark

[slingy1157]

Yep, lap it. I had an old 100cc 4 stroke single once, had the same with the flywheel snapping the key, then undoing the nut and spinning off. Tried all sorts of things. Spot welds-Broke almost instantly, fully welded nut to crank- broke after a minute, steel bar welded across flywheel to crank- 2 minutes. After all this, the thread was fucked on the crank, so i cut it off and welded a piece of HT bolt on, i got some weld on the taper, so filed it back , then lapped the flywheel on to regain the taper and.................sorted, just bolted on to standard tension and never came off again. I would like to point out i was about 16 when all this bodgery went on and had a 9" angle grinder,a mig welder and BFH in the farm workshop as my main weapons of choice for fixing stuff and no real clue lol.

 

[rustychain]

grinding paste & locktite plus air gun  did it for me

[Reinhoud]

The tapers must be different, I don't think you fix it just like that.

 

[skelly]

If the taper is looking proper pants you can start with coarse grinding paste, then go to a fine paste.

Then clean it and blue it.

Tapers work really well at holding stuff, for example morse tapers on machines, cam pulleys on Cosworth BDA engines.

If its lapped and cleaned correctly it will hold without any loctite.

Skel

[KATANAMANGLER]

As per all the other lapping advocates, I had this problem with an ET. I used valve grindind paste heavy course first and fine to finish. When I was happy that I had a good fit and my blistered hands could lap no more I used brake cleaner to clean and degrease all mating surfaces and threads. I used thread lock on the nut and a windy gun to rump it up. Never had any more trouble.

[Andries]

There is no Dowell pin bad design easy solution I used was to spot weld once torqued up spot weld the alternator in 2 place 180° apart to the nut and spot weld the nut the same to the crank problem solved. 

[cnap504]

I should have taken a picture of my fix but didn’t.  I lapped the rotor on the taper and it smoothed out pretty good.  I didn’t do anything to replace the missing metal.  After the lapping I seated the rotor to the taper with Loctite 638 retaining compound and used red Loctite on the nut threads, she’s holding up so far.

Edited June 21, 2021 by cnap504