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Any ideas what caused this crack? I have owned the bike from new in 1975. The cover has only been off a couple of times and I don't recall seeing this crack before but I could have easily missed it. The bike has only done 10,000 miles and never been mistreated. I will replace the alternator and Ducati ignition system but would like to know how the alternator came to develop a crack.

New one on me, never seen that before, can only assume a manufacturing fault?
Cheers,
George

I could understand it if the taper had cracked, but the flywheel........ Hopefully Nigel will see this post and comment. Is there any chance that the flywheel has been touching the clutch gear?


Colin

Never seen such damage, too.
The crack line seems to start from the hole of one rivet in the hub. Are the rivets still all tightly fitted, especially the one close to the crack line?

Hans

Hans - As far as I can see the crack emanates from one of the screws. However all the screws are secure.
Colin - All of the drive train is untouched since it left the factory. There are no scuff marks on the alternator, so I don't think that the alternator and clutch have come into contact.

I did wonder if it was caused by an engine 'kick back' during a failed attempt tp kickstart.

Roger

I remember long ago looking at the assembly and thinking it would be possible for the alternator to carry shock loads from the transmission forces or to come loose.
Perhaps you have a poor fit somewhere , not unknown in Ducati lore.

Considering what ugliness could result from a possible sudden deterioration at speed, I'd consider that too dangerous to ride until the rotor is replaced.
There must be lots of rotors from useless dead Motoplat alternators around, that fit.

I have seen one cracked in the same manner emulating from the rivet. My guess is that it's an issue from manufacture that has just shown up after time. You should be able to pick up a used replacement as many originals have been replaced with either Electrex or Power dynamo units. Alternatively just replace it with an Electrex alternator. The cracked flywheel may last forever, who knows, but I personally wouldn't take the risk and would replace it.

Nigel

Thanks for all the helpful comments on this forum. It is a relief to know that it does not appear to be a common problem: looks like it is a manufacturing defect or factory assembly error. I had already decided to upgrade to 12V and new alternator/ignition. I did not want to go to the expense of replacing the alternator only to have the problem reoccur.
Roger

Imho, the most cost effective way for a repair and a 12Volt conversion at the same time would be buying a used rotor, and a chinese 5-wire shunt regulator (ca. 10£/€). Of course, all 6V versions of bulbs, battery etc. have to be replaced by 12V items.
If you want more power than the 75 Watt of the original Ducati or Motoplat alternator, and a strong and reliable spark, you should think about an Electrex STK-164 sytem.

Hans