Modern Vespa

My GTV got loud this weekend. I guess I didn't check in time. Taking a look now, it seems that the stud has walked out of the head. It doesn't look like it's broken.

Does this look like the case to you guys? Missing, rather than broken? Anybody know the size of the stud? I'm thinking to try to pick up some stud locally.

Studs are 7mm x 37mm (1mm pitch thread). OEM code is 435629. If you also lost the nuts, you'll need heat resistant nuts (see photo). OEM code is: 436947...

Great. Thanks for the quick reply. I have lost the nuts also. From the picture, does that look like a stud loss, or break to you?

Could be broken. Hole doesn't look that deep...

Hate to say but I agree. Doesn't look like an easy fix.

Yeah. I'm fast coming to that conclusion. It looks like I'll be getting some practise with engine removal.

Not sure about a possible breakage. I'd buy a new genuine stud and from that you can work out if there is a part broken stud in the hole. I doubt it, and you will find a new stud will refit just fine. They don't carry much torque load so usually won''t break in the head, it's more normal to shear off flush with the surface of the head.

I can but hope! I have two new studs, nuts and gasket on the way. The scooter's in a local shop at the moment. They're going to have a go at getting the stud out. I must remember to tell them to check there's some stud to get out!

Hi English, interested to know what was the result of your exhaust stud?, had it broken off or was it all missing?

Ah, yes. I should have updated this. Thanks for reminding me.

Well, it's a bit of a comedy of errors, mixed in with a favour from a friend. A friend and I put the scooter on his trailer, and we took it to the shop. I had ordered new studs and a gasket, but they hadn't arrived yet. No problem, I thought, because the plan was to have the shop attempt to get the stud out and, if they did, we would go get the scooter, and I would finish the job.

A few days later, my friend arrived at my door. "Come on, we're going to get your scooter. It's all done." The stud had indeed broken off below the surface of the hole. The shop had been unable to get it out, had drilled it out, installed a helicoil thread insert and reassembled using a bolt.

Now my friend, knowing that a musician and author of a scooter safety book is hardly drowning in money, had already paid the bill, and refused to tell me how much it was! That was so nice of him, if a little embarrassing.

So, my scooter is back on the road, quiet as a mouse. I'm never going to touch that exhaust again (I'll be removing the exhaust at the collar/slip-on when changing tyres from now on), and I still have an unopened exhaust gasket and two studs sitting in the unopened package.

It's not how I planned the thing to work out, but que sera sera...

I wish I had such a benevolent friend!. Pleased to hear it's been repaired and you are back on the road.

That was a generous friend, wish I had one... just went for over $700 in exhaust stud repairs at a service shop.

I saw this Exhaust Stud thread among others ...and thought I'd share my recent event.

Long story... about 2-1/2 years ago my GTS 300 exhaust developed a leak and the shop found a broken exhaust stud. Former (out-of-business) Vespa shop mechanic could not extract the broken stud and instead dropped the engine and drilled out the 7 mm old stud and then re-tapped the hole as an 8 mm, and then installed an 8 mm stud. It never seemed quite the same to me. It seemed to become progressively noisier over the past 2 years. I missed my old quiet scooter and decided to take it to another shop. They determined the 8 mm stud fell out at some point. They removed the engine and tried to install a TimeSert into the 8 mm hole but could not fit one properly. They opted instead to install a helicoil and new exhaust stud (taking over 6 hours labor time). My scooter is now the quiet put-put I remember, I hope the helicoil holds.

Studs shouldn't break off from use unless nuts have not been tightened to proper torque. Maybe that's the lesson to take from these nasty exercises. Or, maybe the studs are too light duty for the application.

A better lesson is probably that sometimes things just break.

If you can remove the engine, an automotive machine shop is a much better choice for removing broken studs and bolts than a scooter shop. No matter how bad you think it is, they've repaired worse.

These kinds of failures are not simple breaks. The exhaust area is one of the most stressed areas of the engine and fasteners shouldn't just break and rarely do with quality design, materials and manufacturing.

I had a stud shear a couple weeks ago, and it's inside the head, like the photo shown here. Time to yank the engine. I'm going to replace the other one too, just in case.

Three exhaust studs break. Better lesson is that they aren't supposed to break...

Speaking for the GTS300, it would help if Piaggio included a torque specification in their service manual. Otherwise it depends on the experience (or otherwise) of the mechanic, so it's no wonder they sometimes either get over-torqued and break, or under-tightened and vibrate off.

The Haynes manual has "Exhaust header pipe nuts 16-18 Nm". It also says (13 pages further on) to lubricate the studs with copper-based grease, which I personally would have done anyway. I can't find any of that in the factory manual. And I have that nagging question as to whether that torque spec applies to dry or greased studs.

My own Vespa dealer did a full nut and bolt job on my GTS300 at the first service. In the process the monkey that was doing the job decided to tighten the exhaust manifold stud nuts so tight that it bent the manifold collar each side so that it was being tightened against the studs. I'm expecting them to break anytime. I didn't notice this until a year or so later so not much point in going back to the dealer about it. This is why I do all my own work these days!

This is a good conversation to those of us who DIY and to let technicians know for those of us who have others work on our scoot's.
Many manuals have a "General Torque Spec's" for nuts/bolts/studs and I use that spec when no specific one is provided for proper tightening of a fastener.
A high temperature thread compound doesn't seem to hurt, especially if you clean it off every time you remove the fastener with the compound on it.
It's very hard to find a good technician...

I know, right? It's like why do they even have a warranty and make extra parts? What's that about? Nobody made this and was like,
-Hey man, you know what would be dope times dope?
-No, like what?
-Like how 'bout if we make these exhaust studs so they are supposed to break?
-You mean make the bike be like Harleyizing up in the neighbors business? That's like dope to the dopest degree.
-We are gonna save a tonelada of lives when we make all these mufflers fall off.
-After we're done with that, let's destroy all the voltage regulators.

"Then let's set up the fuel pumps, followed by regulator high-current connectors to fail!"

Might need to seek a source of better-quality studs. Fasteners come in various qualities (strengths). A stud breaking a bit below the surface suggests that the stud was being flexed, either vibration, insufficient clamping force, or impact damage.

Always leery about replacing a stud with a bolt. Every time you remove it, chance of stripping out the threads (or insert).

If there's room, a larger diameter stud might help.

Metric grade 10.8 for studs are about as good as they get.

Hi. What was the size of the but pictured at the beginning of this thread? The reason I ask is my GT200 nuts are needing to be removed but 10 mm spanner\socket is too big and 9mm is too small! I need more info before I chance removing them.