Modern Vespa

Twice now I've had a strange situation that I haven't been able to figure out. When I bought my 2016 MP3 500 used it had a squeal coming from the rear end at idle but would go away when I drove it. Even when not running pushing it around the garage you could hear a metal on metal scraping sound kind of like the sound break pads make when they need replaced. I decided to replace the belt and look for the noise.
When I got it all apart back there I saw that the bell housing(if that's the right word for it) was scraping against the cooling fins of the clutch. They were just ever so close enough to make a nasty squeal. Inspecting everything I couldn't see why it would be doing that. The bike has only 10k miles on it and everything was in good shape and all the washers seemed to be in the right spots.
Not knowing what else to do I just found a thin washer and put it on the shaft there between the clutch and the housing and that seemed to work. I then maybe put another 300 miles on it since then but it suddenly did it again. My wife and I went for a ride for a few hours and everything was ok when we got home. I put it away as usual but the next time I went to move it in the garage the sound was back. So took it apart again and still couldn't see why it would do that. So I just slipped another washer in and it's good for now.
But it's bothering me as to why it did that and since I didn't really "fix" anything I'm left kind of afraid I put a band-aid on stab wound and I'll have major issues later. I was wondering if anyone else has heard of such a thing or if anyone has an idea of what could be causing the bell housing to come closer to the clutch like that.

Sounds to me like the grease seals inside the rear CVT hub might be starting to let go and hit the belt, which would cause the noise.

I haven't seen grease as such. That was my first thought as well. I was expecting to open the rear end up and see a mess but didn't. And actually you can see how the fins on the clutch are worn from rubbing on the housing. I'm just trying to figure out why or how they could have moved closer together where they would rub.

Perhaps there is a washer or spacer missing. There are quite a few washers holding the rear in and they must be placed in the correct order.

Figured it out! So the squeal thing happened a third time this week. I took it apart and instantly found the problem when the clutch shot out while removing the cover! It appears my problem was the big 55mm nut holding the clutch, spring, and variator together was slowly coming loose and finally came off. So I'm now stuck trying to figure how that happened so it doesn't happen again. I'm thinking of putting it back together somehow but how tight to tighten that nut or will I need to put a type of locktite in there to hold it. Any ideas?

I guess somebody at Piaggio forgot to tighten that nut to spec.

What a surprise.

Glad you figured it out.

When tightened to spec, there is no need for any thread locker compound.

The clutch nut torque value on the GTS is 45~50 nm, I presume it will the same on the MP3.

Wow, that's not very much! Cool, I appreciate that.
I don't believe my clutch was ever tampered with so I'm not sure why it would have come loose like that. I didn't have a wrench or any way to judge how tight to tighten it so I just stood on it to compress the spring and hand tightened it the best I could by wiggling left to right and forward and backward as I snugged little by little. Then when I couldn't do it by hand anymore I took a chisel and tapped it at an angle to turn it a bit further. I was surprised how easy it was to turn with the chisel but it's hard to judge how tight I got it but my guess is it's close since I just tapped it until it didn't turn so easily and not anymore. Thanks for everyone's help!

That torque posted for the GTS does not apply to the MP3.

The torque spec for the driven pulley nut on a current gen MP3 is 92-100Nm.

Call me paranoid, but based on what you found I'd inspect and verify every single nut and bolt on that bike. There is always the chance your bike was the last one to pass through Luigi's hands on his Friday shift before the factory shut down for the annual summer vacation.

To tighten (or loosen) that nut, get two boards. Cut a big hole in one of them. Place the other on the ground, the clutch on top with the nut uppermost, then the board with a hole.

Kneel on the upper board to compress the clutch - you might have to turn it a bit. Now the nut should have no pressure on it and can be loosened or tightened to spec.

That seems like a good idea. I'll try that the next time!