Modern Vespa

Hello all. I am changing my gearbox oil for the first time in a very, very long time (I know, I know...).

The plug came off no problem. However, when I go to reinstall, it won't lock in - I can keep turning the bolt forever and it will not lock in. I can touch it, and it is screwed in, but it is loose. I don't know if it's loose enough to pull out (my fingers are too big) but there is a visible wiggle.

I cannot see any damage on the screw itself.

Could my copper crush washer be totally dead?

Thank you for the advice!

You probably stripped the threads in the cases…

Is there a fix other than to replace the case?

Tap to M10…

OK! I should be able to handle that. Autozone (a US store) rents tools to do that sort of work. Thank you!

Or put a helicoil

I'll look into that (helicoil) as well! Thanks!

I wouldn't use a Helicoil - what happens to the end bit that snaps off? Tapping is quick and easy.

Well, I'm going to tap a new hole, mainly for the cost savings. Because I'd have to buy the whole helicoil kit, it would've been $35 plus tax. This way I buy a new bolt for under $2US and then borrow a thread tapping kit from the autostore for free.

thanks all for the help!

EDIT: Well, I can't tap the hole. There's not enough room where the put the plug on the case of my GTS. The head for the M10 bolt won't fit in the space provided if I'm to use the original hole.

So, this was the plan.
But the M10 bolt won't fit - there's not enough room to make the hole M10 because of the shape of the cover.

I think I'm going to have to use the helicoil method.

Unless I'm not understanding or missing something? But given the GTS design, I can make the hole bigger, but the bolt head won't fit flush on the case - it's too big.

$13 unless you wait until Prime Day, then it's 2 dollars: https://www.amazon.com/gp/product/B01LYNW421/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

A pillow to cry on? Thanks; helpful.
(at least, in the US, that link took me to a $60 pillow)

Can you post a pic?

of what? the threads on the inside of the gearbox or the bolt itself? bolt is solid, as I needed to use it to measure the threads in the store.

so the problem is def. the threads in the gear box cover. and I have no way to get a pic of that.

If is possible in your area, you could let a machinist tackle the job. But you would have to remove the rear wheel, exhaust, etc..... which you are going to have to do anyway to get to the problem area.

Ok, never mind about the pic, I looked at a YT vid that shows what you are talking about. This sucks with the only upside being that with a Time-sert or heli- coil, it will be stronger than before.

OK, thanks!

a time-sert will seal, a helicoil will not. I mean, it'll seal but expect it to always weep a bit.

the "correct" way to do it is with a specialized drain plug repair kit that uses specifically designed drain plugs. however, those are quite expensive and there's not always the room to enact that kind of repair.

in this situation I'd go with a time-sert or source a used cover and replace the whole thing.

Damn, I did not think about the leakage, I'm always learning. So spit-balling here - if the sides of the hole were smooth, would a well nut work?

Would a self-tapping "bolt in a bolt" style work? I see these in the emergency repair section of most auto parts stores.

maybe?

I'd be leery of that type of repair in that I've never really had good luck with expanding type plugs.

my biggest concern is that if it let loose all of the gearbox oil would dump
directly onto the rear tire.

which would then become a game of what happens first: the gear box locks up due to lack of lube, it catches fire when it comes into contact with the exhaust or you make a turn and the whole thing just disappears out from under you.

iffin you're broke down at the end of a dirt road in a shit hole third world country and that's your only feasible course of action to limp it back to civilization? sure, I'd make a go of it.

but in this situation? nah. fix it right, even if it's a week or whatever and a few hundred dollars, that'd be the best time and money you'd ever spend considering the alternatives.

maybe. there's a few issues at play here. one is that it needs to seal, so either the threads have to seal or you need a sealing washer and to use a sealing washer you need enough pressure and for that pressure you need threads for the fastener to bite on and torque up to.

which is where this becomes dicey. there's just not a lot of material there for that type of mechanical attachment.

the second problem is that there's just not a lot of room to work with vis-a-vis the fastener head. most "thread repair" type bolts employ a larger flanged head with a composite or plastic sealing washer as to spread the load, which would most likely be a no-go in this situation.

but could it work? sure. but the likely hood it that it's 100% a one time deal.

If you take that gearbox cover off, surely you can then easily seal the hole? A nut'n'bolt would do, perhaps with a bit of RTV. Then fill the gearbox as normal, taking care not to overfill. That'll last for many 10's of thousands of miles.

nope

Personally I'd use JBWeld (or equivalent epoxy, e.g. Araldite) - but I'd hesitate to recommend this to others for the reasons given above by greasy!

OP, have you looked at the threads on the bolt or in the opening? Do they look crosd-threaded? Generic question, is there a crush washer for the thanks oil?

Another solution would be to go to the SAE size that's just bigger than 8mm. But if you're going to tap this, you want to take it off anyway, so you don't get metal into the final drive unit. At that point, it's likely easier to take it to a machine shop and have them fill and retap it. Or buy a used final drive cover. In the US, that's probably cheaper than going to a machine shop. I'm pretty sure the cover from any Vespa, Piaggio or Aprilia 250 to 300cc scooter will fit.

New, they're fearsome expensive : https://scooterpartsco.com/210-vespa-c-801_802/gearbox-cover-piaggio-for-vespa-gtsgts-supergtvgt-60-p-21634.html

And that's a good price, scooterwest is $150 more...

Another option, drill and tap for this. https://belmetric.com/steel-taper-metric-drain-plug-din-906/?

And you have made sure that the threads are stripped vs cracked case?

A timesert is how I repaired this left side motor case on my '49 Harley-Davidson. It would take a bit of searching and $4,000-$5,000 to replace this case half. So the cost of a timesert repair is insignificant by comparison.

I think it is a good idea, but with no sealing washer, I think it would weep. After looking at all the comments with the possibility of turning into a real safety hazard, I would remove and add a time-sert or take it o a machine shop . The only other good alternate I can think of it picking up one on the used market.

When I see this kind of repair, it tells me the the scoot is well loved. good man, Craig.

nope

Why would it? It's not under pressure, and these types of conical connections are used all over the place, especially in the US, for water and gas plumbing. Hardware shops are full of NPT connectors!

I did not realize it was an NPT thread

It actually isn't - but it's the same principle, a conical thread that seals as the threads bind and (minutely!) distort under torque. Especially when it's steel into aluminum - so the torque has to be *very* carefully monitored. Add a smear of Loctite and all is good.

Loctite makes a product to repair damaged threads like this. I've used it a couple of times and it worked. It comes in a small silver tube and it's not cheap. But it works.