exploding rotor fix?

nonsense said:

. but is there a fix that can be done to prevent explosion if I have the exploding variety (# xxxxx2006) but it is still tight (ok, has an almost imperceptible amount of wiggle)? Or is the only option to get a new one.

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If you feel a bit of wiggle, try this. I tried this trick which worked well. Too well.

Oil wrench, some rubber strips aNd a couple thick washers in a vice clamping the rotor center.

The rotor broke loose with not much torque. Less than 15-20 ft lbs. by my guess and having just done the clutch nut to 40 lbs.




If you have play, just get a new rotor like I did. You can then put a Belleville washer (or two) on it, like I have now with my CNW estart.

mdt-son said:

Rob ss is correct. The early rotor (54212006) is held together by the aluminum casting material only, which is susceptible to creep. The driving force is centrifugal action on the magnets and in turn on the laminate caps and the aluminum casting, imposing radial stress on the latter, which balances through the outer skin. Machining the outer skin does not seem wise in light of this.

The OP claims that failure starts as a shear failure at the centre, allowing the latter to rotate. This is not the case due to geometric interlocking, and interlocking explains why old rotors may exhibit a slight "wiggle" (centre to outer casting play) without failing.

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I never said that centrifugal action doesn't play a role, or that the failure starts at the center (although I could have been clearer about both of those things). I agree that geometric interlocking prevents both of these things. However once the inner is even slightly loose (at the point where it is loose, but is still usable ignoring future wear), the repeated back and forth rotating from speeding up/slowing down will start to exert a hammering and wedge effect on the magnets, pushing them out and greatly increasing the expansion. Eventually the same result will occur just from centrifugal action, but it will be a much slower process, potentially slow enough that by the time it becomes a risk the magnets will have worn out and you will need a new rotor anyway. The washers would also act as a clamp to hold much of the inside alloy to the center of the rotor, providing additional centripetal force to hold it together. The only alloy stretching would then be the outer band. I'm not saying that adding the washers would make it last forever, just that it would slow the expansion down to a point where it isn't somehting you need to worry about everyday, just at the end of the year/ oil changes or even when the engine is due for another rebuild.

As for machining the outer face effecting the strength, you only need to flatten it, so just taking of the Lucas brand name which isn't doing much for the structural integrity anyway.

gortnipper said:

If you feel a bit of wiggle, try this. I tried this trick which worked well. Too well.

Oil wrench, some rubber strips aNd a couple thick washers in a vice clamping the rotor center.

The rotor broke loose with not much torque. Less than 15-20 ft lbs. by my guess and having just done the clutch nut to 40 lbs.

If you have play, just get a new rotor like I did. You can then put a Belleville washer (or two) on it, like I have now with my CNW estart.

Click to expand...

Just tried this. Clamped in the biggest vice I had (old blacksmith vice, ~18" handle) tighened it down... and was able to apply enough torque via the the oil wrench to spin it in the vice (spin it against the washers that is).

nonsense said:

Just tried this. Clamped in the biggest vice I had (old blacksmith vice, ~18" handle) tighened it down... and was able to apply enough torque via the the oil wrench to spin it in the vice (spin it against the washers that is).

Click to expand...

Were the washers only against the the rotor center piece or did they go against the sides of the body of the rotor?

gortnipper said:

Were the washers only against the the rotor center piece or did they go against the sides of the body of the rotor?

Click to expand...

only against the center, I checked that I could see it wiggle by hand after it was clamped, and I could (about 1deg, same as I could see when not clamped).

For lack of hearing any successful experiences (as in "I tried this and after x years the rotor is still firm"), I guess I'll be purchasing a new or non-exploding used rotor. More input would still be appreciated for future reference!

I had one blow up. This one was installed a 650 with a belt drive, because of the width of the pulley there was only about 1/4" of shaft sticking through the pulley. I decided to use an old rotor, but not drive it with the keyway. I machined it so it was flat where it bolted against the pulley, and drove the rotor by two allen bolt heads that stuck out from the pulley about 1/8" those fitted into two shallow recesses I machined in the rotor. The rotor was then bolted on in the usual way with a thick washer. This system lasted about 20,000 miles then it blew up. I won't instal anything but a new one on anything any more. The new ones have more magnetism and give you more power anyway. They aren't that expensive. I was poor in 1992 when I first built this bike so I had to be stingier. I have to figure out a new system for the belt drive bike. I think I will make a shaft extension that bolts onto the pulley.