Modern Vespa

Hi everyone,

I have changed the gearbox oil from my Vespa sprint Veloce and when I was tightening the filling plug I have damaged it.
It had tightened lightly but it keeps rotating.
I have someone that can restore the thread for me but, how do I prevent the debris to get inside the oil pan? Just grease everything to catch as much as it can and then make another oil change and prey?

This is a bummer. Short and first answer, split the case if you are foing to retap it. Although, if stripped out it will likely need a helicoil or threaded insert. Both options require tapping, and risk of getting swarf in the case; which is bo bueno.

A quick and easy fix may be to use a slightly longer bolt, if there are any threads at all further up. I have used a GS or BGM magnetic drain plug in this way, as the threaded portion is a bit longer than stock. Obviously there has to be atleast a few threads intact for this to work. Any bolt of the proper size will work, just be sure it isn't so long as to contact the gear stack

Portugal, right?

I think you are on the right track if you don't want to pull & split the motor. I recently had the same problem and tapped it out to 1/4" NPT. The aluminum debris is relatively benign compared to steel but I'd also suggest flushing w/ a few liters of diesel fuel and sloshing it around best you can while blowing air in the oil filler hole to get out everything you can after tapping. Remove, clean & regrease the tap a few times while tapping should help too.

Be careful tightening if you go this way, the tapered thread means you don't need a fiber washer but you could crack the case if you overdo it. Good Luck!

Ok bear with me, guys, on this "what I would do."
Clean the damaged threads with carb cleaner/acetone and a narrow bottle-type brush.
Mix a small batch of JB Weld and use a Q-tip to smear very little along the threads.
Use a release agent (any oil or grease) on the threads of the bolt and thread it in.
When the leftover epoxy can't be pierced by a fingernail, remove the bolt.
Wait a day and re-install with the washer.

I support this as viable repair. I was recently discussing this technique as an option for a thread repair for a carb stud

I personally have drilled and tapped cases next size up NPT plugs. Like V oodoo said, grease up the drill bit and go slow. Then lots of grease with the tap and keep cleaning and regreasing till you get the right depth for the plug. Flush the case. I always use thread sealant on pipe threads and never Teflon tape. The trick with pipe threaded plugs is to not overtighten them. Just snug them up. You can use steel or aluminum, doesn't matter.

I haven't tried Ray's idea but if I did I would use the regular JB weld not the quick. I have seen holes completely filled, drilled then tapped with excellent results too. I've epoxy bedded many rifle actions and use neutral shoe polish as a release agent (the one in the tin like our fathers and grandfathers used to use). It goes on thin and works great.

I'd expect this isn't going to be strong enough for a carb stud. The JBWeld thread repair trick is measured to only be good to about 10 ft-lbs by the YouTube'ers who make videos about stuff like that.

To the original poster, you can install a helicoil or other thread insert without splitting the cases. Drain the oil afterwards, then either flush the cases or just refill the oil, ride it a little, and change the oil again.

Aluminum swarf will get turned into glitter straight away and it's too soft to do damage to the steel of the gears.

Tap to M10 and don't overtight…

It was only a theoretical discussion about possible fixes for stripped threads. I actually had the case welded, and a steel threaded insert installed.

The JB weld on this application, the filling plug maybe a easy and effective solution, we are talking about the filling and not the draining plug.

If I go to the retaping it will be a familiar that has a repair shop of heavy equipment (forestry), and he has the equipment to do it ,of course with all the careful to reduce the quantity of debries inside.
Reflush with diesel and new oil and everything.
After all of this if there is some debris what is the worst it can happen? It's aluminum on steel, the gearbox has any bronze or other soft material?

I always use helicoil inserts. It is bit tricky on closed cases but absolutely doable.

I would have done the helicoil as well. I would have greased and cleaned the tap every rotation and not bothered flushing the case.

Before you do anything, try this:
Replace the plug with a same size bolt, just a little bit longer, maybe 5mm.
It worked on mine and I was amazed.

A stale piece of Bazooka Joe bubble gym works great as a oil drain plug and you're only out 10 cents.

There is no internal pressure and when the motor's running the level is below the plug. Stick a cork in it.