How bad is it?

After a tracking down a charging issue, I fine tuned the timing, carbs and plugs/wires. I had the bike running the best it has ever ran since I have been working on It and I went for a ride. After about 15 minuets could smell a odd oil/metal burning odour then heard a squeal and then the engine quit (all within 5 seconds) I pulled in the clutch and coasted a few meters to a stop. I still had all my electrical power so I tried to kickstart the bike. the kick petal would not move, I then confirmed that I had it in neutral and tried to kick start it again and it still would not move. I rolled the bike to a safer area and called for a trailer to tow it home. After I got it home and did a quick investigation and I opened the crankcase I found whats appears to be the rotor and alternator melted and fused together, I tried to remove them but they would not budge. I tried to crank the kickstart pedal and could see the clutch sprocket try to move but appears that the melted rotor and alternator stopped by the studs attaching the alternator. what do you suspect was the main cause of the brake down? A short in the alternator wires, the rotor or something else I could be overlooking? I will try to post some pics tomorrow.

blipJC said:

what do you suspect was the main cause of the breakdown?

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Insufficient clearance between the rotor and stator?
Rotor beginning to "explode"?

Perhaps primary to case screws are loose and the alternator is resting on the rotor.
Ta.

Never heard of this happening, but you'll probably have to cut the stator off or pull the whole unit off with a puller as if you were pulling the rotor and cut it off then. I's obviously melted and ruined, but you may be able to salvage the rotor.

Hi.
The rotor is probably wrecked as heat and/or impact are ways to destroy magnets.
http://www.physlink.com/Education/AskExperts/ae472.cfm
Ta.

Heat sink? sounds like excessive voltage was not being earthed out.

I must say, it sure sounded bad at first, but Lab is likely right.
After knocking, cutting, chewing, whatever it takes to get the melted blob off the rotor, it should be just a matter of replacing the stator. I hope.
FWIW, I place .010" shim stock in various places to validate stator clearance all around the rotor.

needing said:

Perhaps primary to case screws are loose and the alternator is resting on the rotor.
Ta.

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By far the most common source of worn/melted stator/rotor. 3, 1/4-20 fasteners hold the primary to the drive side engine case (4 in Mk3); you can also, to some degree, add the primary center fixing stud; do make sure that it is properly clearanced and isn't stressing the cover. If you add up the tolerances in the casting, machining, tapping of the inner primary cover its amazing that most come out with the proper clearance for a stator/rotor.

A friend had this happen on his MK3. The rotor and stator had welded themselves together from the friction during a high speed road test run. This caused the rotor to twist on the end of the crankshaft shearing the woodruff key and making a mess of the crankshaft end. Later they discovered that they had forgotten to fill the primary case with oil before the ill-fated test ride. I think the oil helps with heat dissipation. It was a real mess. The carnage was strewn all over the e-start components too. It smelled like when you overcook microwave popcorn and it turns to black carbon. They had to rebuild the motor with a replacement crankshaft. It was a costly mistake. Hope you got yours shut down quickly enough to avoid this type of damage.

Ugh, there is a known fault of old un welded rotors center casting loosing their centering. It takes more rpm than comnoz spintron can produce to flex crank enough to foul rotor into stator. Electrical over heat tends to swell the resin away from center it fuse don't save it. Possible a chain link piece or something else got in the space. Could be crank broke first?

Hi blipJC.
When you acquire a new stator and rotor you may find setting the air gap easier to achieve by wrapping common 80gsm paper around the rotor until the stator is a snug fit, tightening the stator fasteners then easing the tube of paper out. All round perfect gap every time and no magnet contact with the stator.
Ta.

Ugh, we always read/hear about centering the rotor but in the few I've dealt with the holes in stator are tight enough fit there is nil slack to shift w/o hammering on posts or opening the holes in hardened laminates, ugh. My two were not centered very prefectly and found using a wrap spacer merely jammed w/o centering anything better. My method is shine light behind stator and bop stator a bit to get as even light as possible seen all around. It would be a servere tough task to cut off stator in non ES so hope you and your tricky MK3 surrive unharmed further and simiple exterior reason discovered.

Yes, as I recall we had to cut the stator off of the rotor, then cut the rotor off the crankshaft. All the goofy E-start hardware was in the way and made it really difficult to get access to the stator (after working on the Rube Goldberg E-start contraption I swore I'd never own one). The woodruff key had sheared off and the crankshaft end was spun and polished so badly we couldn't find the keyway. I think they had a hard time finding a replacement crankshaft (e-start crank is unique) because the rotor shaft on the E-starts is slightly wider than the non-E-start cranks.

hobot said:

It would be a servere tough task to cut off stator in non ES so hope you and your tricky MK3 surrive unharmed further and simiple exterior reason discovered.

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Yup, Hobot's right.
The old (pre-welded) rotors had a nasty habit of cracking and coming apart due to centrifugal forces. This starts out as cracks in the casing which begins to expand and then it eventually starts to rub the stator, which begins to heat-up due to the friction which causes even more expansion and more friction until it all welds itself together into a big blob, and locking the motor. Hopefully if you remove the stator nuts and the rotor nut it will all come off together, but if not you'll need a good 3-Jaw puller. Let's see some pictures.

hobot said:

Ugh, there is a known fault of old un welded rotors center casting loosing their centering. It takes more rpm than comnoz spintron can produce to flex crank enough to foul rotor into stator. Electrical over heat tends to swell the resin away from center it fuse don't save it. Possible a chain link piece or something else got in the space. Could be crank broke first?

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I reused those dog bone washers once and ended up with similar mess ... bad stink lots of smoke ... but the bike and I did make it home ... new stator and rotor and all good since ( also new washers every time )
Craig

Crying out loud Mark for the love of commando you cut it all off of a MK3, ugh my great respects. Pray tell what was used to cut it off? I've had a life time of trying to saw stuff off w/o damaging surrounds or insides but I'd just torch off and start over myself. One fun example was helping my late brother Dale put a chimney though wall with a 2x4 stud between two hard slabs no drill, saw or hand could quite reach, so asked for his compact .22 semi-auto to put 10 chew holes above and another clip of 10 across bottom to get it so knife could finish the cuts w/o peircing the wall and got the vent to clear fine. Ricochets would prevent this fun way on Nortons though. When Peel over rev'd the SUPER high frequency and deformations backed out a belt pulley plate screw that took a couple hundered miles to fully come loose so imagine my heart sink as Peel made a little Squerch and siezed as I idled into shed about to stop - and my elation on pulling pulley and screw dropped out and engine was freed. Put back and did most of 2000 more miles, and didn't even bother to grind out the slag of melted stator resin with ablated stator laminates, but eventually did and sold the BBQ'd darkened Sparx 3 phase off at a ralley still working fine. Btw I never eat what I shoot. Strangely my brother's surprise death and Peel's both tend to flash back about same frequency but Dale's loss relieved family loads while Peel's added to em. Make those sparks fly while ya can eh.

Hobot, we used a small air powered grinder with a cut-off wheel attached. We were limited to where we could cut due to the E-start bracket which surrounds the stator.
We had to peel the stator apart in layers like a steel onion. Once we got the stator off we could remove the E-start parts and work on the rotor in the clear. We tried a puller with heat but it wouldn't budge. We were forced to section the zinc rotor casing with the cut-off wheel, might have been a cold chisel along the way too, until we got down to the steel inner sleeve that contacts the crank. It was a bear not cutting into the crankshaft, but later we discovered the crank was toast anyway. Ugh...

Never heard of ballistic remodeling before. That must have been a first!

My bike had rotor/stator misallignment. It heated up the windings and ruined the stator. That's how I got the opportunity to buy the bike from a friend who was completely frustrated with it.

Once I figured out what was wrong and replaced the rotor and stator, I still had to oblong the mounting holes in the stator to get the part mounted with the proper gap all the way around it. I've had no trouble since I rebuilt the engine with superblends and adjusted the rotor/stator gap.

Good luck removing that mess. I might just unbolt the stator and vise grip the stator studs out of the casting. Then use a puller on the stator to see if it will break free of the rotor,... then use the puller on the rotor to see if you can get it off the crankshaft... Sometimes a few gentle taps with pressure applied makes things pop without breaking..

Those 1/4 bolts don't have a lot of thread in the alloy block either. I left out the lock plates to gain
an extra thread and loctited them in.
No problems so far.
It isnt just Nortons that have alternator melt problems. And since most later model brit bikes use the
same lucas bits mostly the same story.

On a Cdo I care to modify - I put in 3 small studs instead of bolts with red loctite for a number reasons. Thanx for the nasty details Mark as I would fear my use of grinding disc being snatched into corners chewing on vitals - so a nod at you and crew staying within the lines. I tend to loose a groove of flesh focusing on grinder not getting out of control too much. Main ballistics I care about is when Peel snatches a turn so harshly one or both tires leave surface so much plan on that to land just right every time.

There is standard .45 ACP and +P ACP and more expensive wear/tear Navy Seal +++P .45 Super ballistics I use now and then a shop helper.
https://www.youtube.com/watch?feature=p ... kBER69aaNk