Modern Vespa

Hi everyone,

As a quick update, my GTS has so far suffered two broken exhaust studs in its short, one-year life--both are implicitly blamed on the Moto Amore bronze bushing, although not by me. Yesterday, about 20 minutes into the ride home from the shop that fixed the second break, both of the nuts backed off the studs, leaving the collar hanging down by the clamp and hot gases pouring into the engine compartment, which halfway melted a bunch of cables running past the downpipe.

Any ideas about what might have caused them to come off so soon? The roads were smooth, the tires are fresh, and the rear suspension settings on both sides are the same.

Thanks!

Scott

Although others do have the occasional broken studs when an attempt to remove the nuts is made - those with 'solid' exhausts seem to be the only ones who have this happen on the move.

The modified downpipe with conventional graphite collar would be my choice...

Jim,

Mostly because of your encouragement, I had the mechanics put the original graphite collar back on the exhaust during this last repair. The nuts actually backed off of a completely stock exhaust setup.

Scott

Then they weren't done up tight enough. End-of.

my thoughts exactly.

although a distant possibility: bad thread on the nuts. if they've been on and off several times it's entirely possible that the nuts are just plain wore out.

best,
-greasy

That's the shop's idea, too, so they're going to tow the bike back in (for free! nice folks) and put some new ones on. Hopefully that'll be the end of my exhaust problems! Right...

You're right, of course -- an exhaust without the benefit of some "give" is more prone to a variety of other breakages, especially if the pieces aren't assembled perfectly aligned. Piaggio's solution allows for some slop in assembly and some movement during use.

That said, Piaggio's solution also sucks balls, and is far more fragile in several other respects than a solid (or even brass-bushing'd) exhaust. Even Piaggio techs, otherwise competent individuals, manage to regularly botch the installation of the exhaust gasket for no other reason than it is a delicate, fragile part that must be fitted with the utmost care in a location that is a pain in the ass.

I'll take the solid exhaust any day. Or an LV pipe, since I know how to install it so the header won't break. You can keep your graphite bushing that blows out whenever someone nearby sneezes.

They are cheap as chips here (less than GBP10) so replacement every 12,000 miles or so is of no consequence.

They're like $30 here, and for some people they blow every 4,000 miles or so. Really depends on your mechanic and how invested they are in getting it right.

And with the graphite bushing, you only get one chance. You damage it during installation, and it's time to throw it out and take a new one off the shelf.

True, but if a shop mechanic no problem to the owner, surely - and if self-inflicted, lesson learned.

Scott: Our GTS has the Moto Amore bronze muffler bearing. It's been on the exhaust for about 1000 miles. My wife is the only person who rides this scooter and it hasn't had any exhaust problems. I've read about your constant problems with the broken exhaust studs (and those of a couple of other posters) so I have been checking the exhaust studs every week for the last seven or eight weeks and I don't see any evidence of any problems developing. Like you, I don't understand why some scooters are having a problem and others are not. I'm not convinced that the bronze bearing is the problem but hell, I don't absolutely know that I'm correct. I do know that there are quite a few of these bronze bearings that have been installed and there are only a handful of people (that I could find) who've had a problem. There seems to be at least as many riders (or more?) who are using the stock, graphite bearing that have also suffered from the same problem.

I posted once before that I have about 12,000 miles on the Moto Amore "muffler bearing" and it is holding up fine to the best of my knowledge. Maybe I'm wrong but in theory isn't the exhaust header bolted to the engine and the three mounting bolts for the muffler bolted to the rear of the engine (transmission) so they all move as a unit? Granted that the muffler travels up and down a greater distance but the pivoting of the engine should keep everything in line and there shouldn't be a strain on the header pipe. That is why I would think the "muffler bearing" or a welded pipe should not make any difference. I would think the key would be that the nuts on the header were always kept tight. Anyone have any thoughts on this?

Like you MichaelR, my bearing has been on almost as long as yours. Problem I had in the begining was the bearing walking up the header pipe (I put to much anti-seize compound on inside and outside of bearing). I put a second clamp on the header pipe just in front of the bearing to stop it from sliding out of place.
I think that maybe now the tailpipe can slide on the bearing, and that is keeping the studs from stressing. Just a guess tho.

This is a great thread, definitely the best exhaust failure thread from the exhaustive list of them that we've had. It is packed with lots of good advice from people who really know their stuff.

But now I am perplexed. I had thought the Moto Amore sleeve was the simple answer; now apparently things are more complex. I'm thinking the gasket failure always gives fair warning as the sound gets louder*, and the parts for the fix are cheap, but breaking a stud is a really bad thing which is hard to fix.

* 3 exhaust gaskets blown so far on my GTS (only 1 brake melt); always a couple of hundred miles of warning.

Interesting what OneEyedJack said about the Moto Amore "muffler bearing" migrating up the header pipe. I put a lot of anti-seize on mine each time I have had it off and now the clamp is barely covering the slits on the muffler pipe. In fact last time I had to reposition the clamp to stop it from leaking. I had even considered a second "muffler bearing"!! I kept thinking I was doing something wrong when I put it back together. I was afraid to try and get the "muffler bearing" down any because it would put stress on the header pipe . A second clamp seems like a good solution. Did you just get a second clamp from Vespa or make something yourself OneEyedJack?

Oh FFS - the temperature differential down the exhaust chain is huge. 250C+ out of the manifold at maximum (I understand 400C has been recorded). Less than 100C out of the back of the exhaust.

This makes for several millimetres of expansion down the chain. Fixed bolts both ends do not work. Posts passim.

jimc makes a lot of sense, I didn't take into consideration the temperature factor. Seems like I may be on borrowed time here.

Absolutely correct. Even with everything bolted together in unison, there's movement of the parts, and it's not even.

I've got an exhaust leak that sprang up right about when my belt went bad.
I'm going to have a local bike shop do a smoke test to see exactly where it is, but it sounds like directly under my seat.

If I have to get at the exhaust maifold, which is the best way to do it, from the bottom on the stand, from the top, or on a lift (which I don't have)?

Are you sure it's an exhaust leak? If it sounds like it's coming from under the seat, it could be the intake. If the air filter becomes disconnected from the throttle body, it'll get quite a bit louder than usual. Take a peek under there to see if anything is loose in the intake system. The airbox has to be unbolted in order to remove the belt cover, so it's very possible that part of the intake came apart while the airbox was being moved around.

It's accessible from underneath, when the scooter is on it's stand.

Run your hand from the muffler forward along the exhaust (on a cold bike!) you can reach right up the manifold to the engine (& studs). After that start up the scooter and feel around the clamp- you'll be able to easily detect if your exhaust gasket is blown. I suppose you could check for broken exhaust studs the same way- but you'll have to be quick!



Harvey

OK, so the air filter icover s just those two long bronze screws that I had to undo when replacing my belt, right?

Does it pop open to reveal the air filter, or am I looking for a disconnected hose up stream?

Thanks Harvey. If the exhaust gasket is blow will I be able to feel it, or have to do a visual inspection on it?

I think you should be able to feel the hot air coming out of the joint where the muffler meets the downpipe with your hands. Also, if you want to make sure your studs are intact--when mine sheared, the noise sounded exactly like it was coming from under the seat, right from the heart of the bike--you can lay on your back, slide your head under the pipe and take a look at where the pipe meets the engine. This is obviously best done when the bike is cold, unless, of course, you want to melt your face off.

I just used an ordinary worm clamp. See pic
Bearing stays solid to header pipe but can slide on exhaust pipe.
Keeps bearing from sliding forward of the slits on the exhaust pipe.
About 9,000 miles so far - no problems.
Best, Jack

Sounds like the SAS (Secondary Air System - a kludge) pipe has blown. Cheap to replace, even cheaper to remove and blank off.

That's good news. Can you show me where that would be in relation to my exhaust manifold?

Wait, I thought we were talking about a GTS... there's no SAS on a GTS.

Perhaps someone will try to make an aftermarket exhaust stud made of a better alloy. The material they make grade-8 bolts from is around 3 times stronger than the average stuff.

[It would appear that Piaggio should use larger diameter studs. There probably isn't sufficient material in the head to use larger diameter studs. If anyone has a trashed head to experiment with...]

Abject apols for the brain-fart...

OK, I started my scoot up and while on my back I was able to look up and see a pretty stout collar attachement. It was before (downstream) of the MAP sensor. Around the edges of this collar I felt exhaust coming out from several holes, but the holes look like they are designed to be there. The holes are on the ends if lines cut in the exhaust, and are probably meant to allow the clamp to compress the exhaust at that point without the cuts exceeding past the hole area.

Is the large clamp meant to cover these holes, and has thus slipped, or is there another clamp that is supposed to be there that has fallen off?

Btw, I used a mirror to see if my exhaust manifold studs and bolts were there, and they appear to be in place.

Because this is downstream of my MAP sensor, I should be fine as far as the computer adjusting the air/fuel mix, I'm thinking.

OK, either the collar is shot (they have a finite life), or has wriggled out from the exhaust and up the downpipe, thus exposing the slots to the gases.

I agree with JimC. Time to pull the muffler and look at the graphite gasket that sits where the two pieces of pipe join up.

The clamp positioning is normal- it's not designed to 'cover' the slots (which are there to ease the fitting of the muffler pipe over the malleable gasket). As for the exhaust from the slots, I'm interested in expert opinions on this. I changed mine out for that reason, but I may have over-reacted.

Harvey

Looking at this picture from OneEyedJack's scooter, is this the area where they join and this graphite gasket would be?



Btw, his worm clamp is now covering those holes I mentioned on my post.

Edit: No, I think his worm clamp is on the other side of the areea with the holes.

The clamp should not cover the holes at the end of the slots, as per official Piaggio guidelines. If exhaust is coming out there, then it's virtually certain that you've blown the exhaust gasket.

Yes. I don't think so. The worm clamp is a stop to keep his brass bushing from sliding out. If you look at top of the larger of the two clamps, you can see one of the holes at the end of the slot. This clamp is correctly installed, not covering that hole.

OK, so does the exhaust gasket sit where the exhaust meets the manifold, or is it underneath that big clamp?

Yes, that's the place. It's inside the pipe where the two pieces join together under the clamp. The picture that you referenced is the old style pipe that doesn't appear to have the exhaust collar that is on the newer models.

I don't think so. The worm clamp is a stop to keep his brass bushing from sliding out. If you look at top of the larger of the two clamps, you can see one of the holes at the end of the slot. This clamp is correctly installed, not covering that hole.[/quote]

I edited it because his pic is upside down from the angle I saw when I was on my back.

I think I will try and shoot some pics of mine and let you guys see what see.