Modern Vespa

Last night, a friend of mine (riding a bike I sold him, my ex-red GTS250) called me from the side of the freeway, needing assistance. He was riding home from the Scoot to the Moon rally, and had put a lot of miles on during the day. Just a few miles from making it home, his exhaust had fallen completely off the bike, and was lying 100 yards back on the side of the road.

The exhaust is demolished, bent and battered. The exhaust studs holding the exhaust header to the engine are snapped off. The lambda sensor is now a delta sensor, and the wires that lead to it are but little pins sticking out where the plug used to be.

In order for this failure to occur, all three of the M8-sized bolts that carry all the weight of the exhaust would have to back themselves out. They were stainless steel bolts in an aluminum surface (the swingarm plate) and they had lock washers on them. I know, because I always put lock washers on them whenever installing an exhaust.

Once those three bolts were out, of course, all the weight gets transferred to the exhaust studs at the engine head, and they can't take the weight of the exhaust bouncing around. I completely understand how those would have snapped (and that's going to be a bitch to fix).

But the three bolts that carry all the weight mystify me. I just don't see how they could have backed out of the swingarm plate. And no, they're not sheared off. I checked. The holes are empty.

So, I ask, incredulously: anyone else ever have your entire exhaust just up and fall off?

The only time Iv had them bolts fall out 2x ( well one lost and other half out and just holding exhaust on ) was on my typhoon125 , I think I put too much copper slip on bolts and they just slipped out on the lube they also had lock washers
Now I just put a very light amount of anti-seize on bolts

Ack! That sucks.

I install mine dry, though.

I've never had exhaust mounting bolts unwind themselves. I did have the two swing-arm mounting plate bolts unwind once on my Fuoco - it must have done quite a few miles before I noticed, no difference in ride quality! That must have been down to my own incompetence though. I bet I installed them finger-tight before doing up the axle-nut, and then must have forgotten to tighten them properly.

Something similar may have happened to your friend.

It's possible, but those would have been my fingers.

Honestly, though, it doesn't seem like something I would do...

I was very certain I wouldn't have left my bolts un-tightened as well. I've never done anything like that in 40 years of tinkering. However it's the only rational explanation.

There's another explanation I thought of -- he keeps the bike outdoors (as I did when I owned it) and it seems possible someone would have tried to steal the exhaust for the catalytic converter that they might have imagined to be inside. After all, Piaggio equips the exhaust with Torx-head bolts, presumably for their added anti-tampering properties. I replaced them with normal allen-head bolts, of course, in order to minimize the number of tools I had to carry around with me.

I can imagine some dumb thief trying to steal the exhaust, and then realizing he doesn't have a quarter-inch-drive 6" wobble extension with a 10mm socket on it. That would effectively keep the exhaust attached to the bike, although not for very long.

(this particular exhaust had the header welded to the exhaust, as an all-one-piece solution to the dreaded exhaust gasket).

I can't completely rule out any of these explanations, but I wanted to query the wider MV audience to see if anyone else had ever experienced a genuine loss of those bolts for no good reason.

Maybe someone was half-way through stealing the exhaust and was interrupted, leaving it hanging by the manifold bolts only? Was it a stock exhaust, or something exotic?

It was stock. Nothing exciting.

Actually when I read your post the first thing I thought of was tampering by a thief or someone wanting to cause havoc.

Had it been to the dealer recently? Do you have to take those hanger bolts off to get to something to be serviced? I have had that experience (not with exhaust), where things were not entirely "buttoned up" after a service visit.

...... maybe the bolts were just finger tight. I really don't think someone would want the muffler..........well maybe. I guess there's been stranger things happen.

Just lately I've gone back to check bolts I knew were tight on my scooter and motorcycle. Sometimes they were only finger tight.

I've done that as well. I was 20 miles from home before it struck me that I didn't remember torquing those bolts down. I rode home nervously to find the bolts still there (but loose). Tightened them down with no permanent damage.

We're all human, you know.

P.

Nope. This particular bike hadn't been to the dealer much while I owned it (I did all the service) and I don't believe my friend has had it serviced in the short time that he's owned it. Thus, if there was a failure to button it up, it would have been my own.

It doesn't strike me me as likely a thief boosting catalytic converters would recognize that a scooter had one, or that they would prefer stealing that over a car's. Sorry.


Regards
Harvey

Still, you would think that if improperly tightened bolts were slowly backing out over time that the noise made my the vibration of the exhaust would have eventually caught the attention of the rider.

When I had a snapped exhaust bolt on my ET4 some time back, the ringing rattle, while not instantly noticeable (the sound wasn't like an "OMG!, I better pull over right now!") is was persistent enough to catch my attention and cause me to search for the source.

I remember a previous thread some months ago where the OP was also complaining of a rattle he couldn't trace down that turned out to be a loose exhaust bolt.

I'm not sure how different it would be on a 250, but I can see a rider taking off with missing bolts due to an attempted theft, and not really noticing a difference right way (until everything fell off, of course) more easily than a rider scooting around with loose bolts over a long period of time and not noticing something amiss.

For what it's worth.

+1

I'm also wondering what effect the stresses of thermal expansion and contraction might have had on a 'solid' exhaust.

Generally, we can expect the exhaust to break where the main tube is welded to the can itself. I've seen it happen, and it's an expected side-effect of welding the exhaust solid. You're usually left with a 1 or 2mm gap between the tube and the can, which you can tack weld in-place, remove, and then completely weld all the way around.

It was me! I'm the friend in question. Annoyance and upcoming expense aside, my overwhelming thought is almost laughter... as in, "I can't BELIEVE this happened." The bike looks SO WEIRD missing everything to the right of the rear tire.

I've put maybe 700 miles on it since I got it from Jess, and in that time haven't hit any ditches, potholes, parts in the road, bodies, etc... so I think it was just one of those weird Acts Of God.

Possibly the worst part of it was was being stuck for a while in the wind tunnel of the 101/280 split... I'm extremely fortunate that Jess came to my rescue (Jesscue?) but damn it was COLD! I don't think I've ever been happier to see someone...

-mig!!

Myself, I don't think tampering was likely-- yep, I keep it outside, but usually behind the building (not visible from the street)... and I live in Alameda (rather safe/quiet) and in a super public area (next to City Hall and with lots of neighbors). Like I said, I think it was just one of those weird Acts of God.

Yeah, it was a long shot. I would have expected that to happen in front of my house before it happened over where you live.

(as an aside, my Mother In Law had her catalytic converter cut out of her car in the middle of the night once... it does actually happen)

I doubt that the bolts would have backed out on thier own if properly torqued, I believe someone tried to steal the exhaust. Maybe they had purchased an after market one for thier own scoot and realized it was junk and wanted an OEM one.

Any recent pics of the scoot pre-trauma that might shed some light on the failure?

I've had the bolts come out of my former ET-4, same bolts. I also use anti-seize, and check them periodically. They are occasionally "not tight", although not neccessarily loose (except the ones I lost).

I suspect the aluminum brace they thread into and steel bolts react to thermal cycles differently, and they work themselves loose via hot cold cycles. (thermal expansion?)

I'm no scientist...but I play one on MV

I know this is a long shot Jess, but what about dis-similar metal fatigue? I notice you said you replaced the original galvanized torx screws with stainless steel. Perhaps this aided the properly torqued screws to back out?

Huh, that's curious.

I myself am not ruling out the improper torque scenario - after all I did suggest that on the phone

And yes, Jess, I hadn't thought about it - but people are way more likely to fuck with a bike outside your house than in Alameda

I still think it's the torque, but Starr, your theory sounds cooler than mine.

Oz, I was going to suggest cross club rivalry as a theory, there must be a consipracy theory fan or two online, right?

I do kn that in the Harley Davidson world it dose happen guys lose slip-ons when riding. I test mine from time to time and have put on thread lock sine my 2 bolts have backed out on my HD.

I can see this as a problem if we don't warm up engine before a ride.

I like the X-Files, and I like Fringe!

I also think that's mildly insane Or egomaniacal. Take your pick.

decisions.....decisions......

I saw this happen to a Piaggio scooter in Cuba. It was a 50 cc rental bike, and the bobbing exhaust was held on only by the exhaust bolts on the cylinder. The remaining five identical scooters in the fleet were ok.

I guess we should use Loctite to be sure.

Cheers,
Bob

Anything is possible, I guess, and I'm no metallurgist, so I can't really say whether that would be a factor or not.

Of course, all my other bikes are identically equipped...

This is an easy case. It used to be Jess' bike. Someone had wood for Jess. That person saw the bike and wanted to screw with him.

Probably some mutt that was pissed about getting red slashed circles instead of targets.

There's more than a passing possibility that this could be true based on some of the hostile posts concerning Jess that I've read on another scooter forum.

FWIW I've had 2 exhaust bolts back out on their own (separate instances). Luckily both times the other 2 stayed in.

Stainless bolts screwed into aluminum. The Al expands more and faster than the stainless; the "hole" gets bigger; the screws are now loose; vibration backs them out. I have seen it happen in aircraft and medical devices. And no, LokTite won't work in a high heat environment. The cad plated bolts that were probably original were a better choice than stainless. The cad probably adds some "stick".

Ahem - the aluminium bits are at ambient temperature - or very close.

Poorly insulated exhaust bolts might be a bit hotter. Guess which one expands... But the exhaust bolts are also well distanced from the heat, so I have no worries about heat differentials between bolts and their seatings.

I'll ask Jess's question slightly differently, has anyone with a conventional OEM exhaust have these bolts unravel?

Now THAT is a very likely scenario.

As for the Act of God, I wouldn't go that far to call Jess God