Modern Vespa

The mirrors on my 2019 GTS300 are driving me nuts. They are constantly coming loose. I now carry a wrench in the glove box to tighten them. I snug them down to what I think are near the limits of the thread. Kind of difficult to get a torque wrench on them
Are there any hacks to tightening the mirror nuts without stripping them?

I don't know specifically about that use case, but I would think a generous amount of blue loctite would do the trick. Reversible when you actually want to remove them.

edit: someone with more knowledge than I advises against this so...this is probably not a great idea.

I assume that the 2019 Vespa, whether pre-HPE or already HPE, already has right and left-hand threads on the mirrors.

It's actually quite simple: Unscrew both mirrors (turn towards the back). Screw the sleeve with nut completely onto the respective mirror by hand AND THEN TWO TURNS BACK. Then screw the mirror in first, turn it in the direction of the mirror glass until the sleeve comes to a stop, then unscrew it in the opposite direction until the mirror arm is centered between the handle and the brake lever. Hold the mirror arm firmly and now lock the sleeve with the nut until it is hand- warm (same direction of rotation as screwing in the mirror, in each case with the mirror glass). You don't need much force!

My guess is that you have screwed the sleeve with nut completely onto the mirror, in which case you are missing the thread path for countering (which is why the sleeve with nut must be turned back two turns).

DO NOT USE LOCTITE (or similar)!

Are you missing the dome washers?

That is a good possibility. Tell me more about them. I don't see any reference to them. I am guessing that I have to buy new mirrors to get them.

I have primavera mirrors on my GTS HPE. They came with one flat and one dome on each side. Without them the mirrors would always come lose.

I don't know if the GTS pre-HPE had these but if not go to the hardware store and buy some generic ones.

https://www.sip-scootershop.com/en/product/lock-washer-mirror-piaggio-for-vespa-primavera-sprint-50-150ccm_PI012538

I don't understand your reason for backing off the locknuts by two turns.

On my GTS (admittedly an older model, both stems are RH thread) I spin the locknuts all the way up the mirror. Mount the mirror, and when it gets to the end of the travel, undo it again until it lines up with the end of the bars. Then do up the locknut "good'n'tight". Haven't had a problem on any of our scoots unless some numpty bumps against them while in the garage. No idea who that could be...

The method described above works perfectly without washers.

you should try the rough roads I do

The roads in Germany have become so bad that I think the humpy outback roads of Australia are better…

So you'd feel at home riding like this?
https://www.instagram.com/reel/DCGYkYPv53b/?igsh=am1zOTQ2OGhiY3Jr

(I kill clutches etc on 4WD roads as a hobby)

The mirror system on the Vespas and BVs work fine. Never had one come loose when tightened up as suggested by JimC.

I put spring washers from the hardware store on my bv350.

By spring washers, are we talking about Bellville, split washers or something else ?

No washers on any mirrors here, nor have there ever been on previous scoots.

I've just taken the mirrors off my 310 to do some stuff at the headset. Don't recall seeing any washers either and I'm not the sort of guy who would miss that detail.

Why on earth would there be washers anyway? The stem does not tighten down onto the headset, only the locknut does that.

Belleville washers are usually called conical washers. Split washers are as the name indicates. Spring washers are typically made like this -