What happens when belt breaks?
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Wed Jun 05, 2019 4:09 am quote
I am curious on what happens when a belt breaks when riding. I imagine that if you are cruising at a steady pace and the belt breaks, the rpms will go sky high (hit a limiter?) and a loud noise from transmission case area?

Pretty much the same from a standing start when belt breaks?

Coast to side of road, get your spare belt out and make a change but what damage can be caused inside the transmission case?
eeee-bip
Benelli TNT 125 "Bean Alley" Kymco AK550 The War to end all Wars
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Wed Jun 05, 2019 4:11 am quote
Slip
There's a thunk noise and you coast to a halt at that side of the road.

Then you curse yourself for not changing it.

Normal use 6000 miles. Cannonball 4000 miles Ironbutts 2500 miles.

Bill x
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Wed Jun 05, 2019 4:15 am quote
OR
Your doing 70 on a wide bend in the road and the belt breaks, gets jammed in the clutch, locks the rear wheel up and you do cart wheels in the median for 100 feet while Jess watches from behind in ammasement that your are still alive with no broken bones.
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Wed Jun 05, 2019 4:29 am quote
Muscle
I was lucky. Mine just turned itself into candyfloss and just sat there shredded mocking me.

My fault, 2 rides . 1000miles non stop then 1500 miles non stop.

30 miles later total stop.

OEM Belt.

Bill x
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Wed Jun 05, 2019 5:09 am quote
Re: What happens when belt breaks?
wbdvt wrote:
I am curious on what happens when a belt breaks when riding. I imagine that if you are cruising at a steady pace and the belt breaks, the rpms will go sky high (hit a limiter?) and a loud noise from transmission case area?

Pretty much the same from a standing start when belt breaks?

Coast to side of road, get your spare belt out and make a change but what damage can be caused inside the transmission case?
good luck changing a shredded belt on the side of the road, fibers are wound around clutch deep inside. Do you carry a breaker bar to get the variety nut and clutch nut off?
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Wed Jun 05, 2019 5:22 am quote
Re: What happens when belt breaks?
old as dirt wrote:
wbdvt wrote:
I am curious on what happens when a belt breaks when riding. I imagine that if you are cruising at a steady pace and the belt breaks, the rpms will go sky high (hit a limiter?) and a loud noise from transmission case area?

Pretty much the same from a standing start when belt breaks?

Coast to side of road, get your spare belt out and make a change but what damage can be caused inside the transmission case?
good luck changing a shredded belt on the side of the road, fibers are wound around clutch deep inside. Do you carry a breaker bar to get the variety nut and clutch nut off?
If I was doing a long distance, multi-day tour, I would carry the necessary tools. Although, I would also make sure that the belt would not exceed the recommended change interval during the trip or change it before the trip or during the trip prior to that interval.
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Wed Jun 05, 2019 5:56 am quote
Re: Muscle
Bill Dog wrote:
I was lucky. Mine just turned itself into candyfloss and just sat there shredded mocking me.

My fault, 2 rides . 1000miles non stop then 1500 miles non stop.

30 miles later total stop.

OEM Belt.

Bill x
That's what happened when the belt broke on a rented GTS on The Great Ocean Road just north of the Twelve Apostles.
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Wed Jun 05, 2019 6:02 am quote
A friend has a Big Ruckus and was telling me about his FleaBay $40 belt shipped! Later that night, he's on the side of the road at 2am waiting for a tow-truck. Belt snapped with only 40ish miles on it! Cheap belt, cheap results. I had a TST variaor on a Zuma 125. That variator was trouble from day one. Left my wife and I stranded on the side of the road waiting for a tow-truck. TST went in the recycle bin. Both of these instances resulted in shredded belts. No wheel lock up. Neglected the service on a Helix back in the day and the belt snapped and got wedged in the rear torque driver, at speed. Didnt lock the rear wheel but the scooter slowed down really fast. Of course I was on the freeway doing 60mph. Waited on the shoulder for a tow-truck and got ticks AND chiggers!
Molto Verboso
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Wed Jun 05, 2019 6:15 am quote
When the belt on my BV200 broke while riding at 55mph the rear wheel had nearly locked up. It was like extreme hard braking without sliding. I credit the grip of the City Grip. Later when putting it on the trailer, the wheel was completely locked
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Wed Jun 05, 2019 6:38 am quote
I have had four belts break while riding.
And the variator nut came loose three more times.
No real drama in any of these.
Going fast, mine just rolled to a stop.
On all of these I could feel it falling apart, just hoping I could get to my destination.
It is not a difficult fix on the side of the road if you carry tools and parts.
I now even carry a mid length breaker bar under the seat.
But knowing they fail, I usually leave on long trips with a new one installed.
Bill
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Wed Jun 05, 2019 7:14 am quote
Re: Slip
Bill Dog wrote:
There's a thunk noise the engine cuts out and you coast to a halt at that side of the road.

Bill x
Mine happened at 100 km/hr going up a slight hill.
I towed it in and did it myself.
We added a second washer on the front split pulley to prevent the two halves closing too far.
I lose a km/hr or so top end but it runs smoother.
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Benelli TNT 125 "Bean Alley" Kymco AK550 The War to end all Wars
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Wed Jun 05, 2019 11:25 am quote
Much
Forgive the highjack but the belt on a Kymco AK550 is supposed to last 48,000 miles.

Yeah, right.

Nill x
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Wed Jun 05, 2019 12:20 pm quote
Re: Much
Bill Dog wrote:
Forgive the highjack but the belt on a Kymco AK550 is supposed to last 48,000 miles.

Yeah, right.

Nill x
How long does Yamaha say it lasts? The Kymco AK550 and 2017 and newer Yamaha T-Max 530 share a transmission, and use the same belt. If Yamaha says it lasts that long, I would believe it.
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Benelli TNT 125 "Bean Alley" Kymco AK550 The War to end all Wars
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Wed Jun 05, 2019 12:23 pm quote
Ask
I don't know. Look it up.

Bill x
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Wed Jun 05, 2019 1:23 pm quote
I've had 2 break on me, both on a Honda Elite 250. The belt change interval on that scooter is 12,500 miles. The 1st break (22,000 miles) the belt shredded about 6 teeth and I was able to limp about 1 mile home. The second break was 20,000 miles later and the belt snapped when I accelerated from a stop and I had to hitchhike home. Simply felt like the bike jumped into neutral. I knew immediately what had happened.
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Wed Jun 05, 2019 1:32 pm quote
Sometimes the broken belt makes bigger damages. Very risky.
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Wed Jun 05, 2019 1:35 pm quote
Had a belt break, and it shredded. I dug really good and thought I got all the fuzz out, I didn't. A few months later I was replacing bearings in the trans because they took a seal out.
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Wed Jun 05, 2019 1:36 pm quote
WEB-Tech wrote:
Had a belt break, and it shredded. I dug really good and thought I got all the fuzz out, I didn't. A few months later I was replacing bearings in the trans because they took a seal out.
For example.
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Wed Jun 05, 2019 4:00 pm quote
WEB-Tech wrote:
OR
Your doing 70 on a wide bend in the road and the belt breaks, gets jammed in the clutch, locks the rear wheel up and you do cart wheels in the median for 100 feet ....
Huh? Care to explain how exactly a broken belt can get “jammed in the clutch” and “lock the rear wheel up”?

You can't lock up a CVT scoot for the same reason you can't bump start it. The engine must be turning roughly 2,000 RPM to engage the clutch. If a belt breaks the clutch disengages. It doesn't matter how fast the rear wheel is turning, with no belt, the clutch is disengaged. A broken belt is less likely to “lock up the clutch” than it is to sponantously cause your hair to catch on fire.
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Wed Jun 05, 2019 4:05 pm quote
You might want to do a little more reading on the subject. Lockup’s can happen
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Wed Jun 05, 2019 4:11 pm quote
Educate me how a belt jammed in the clutch could cause the rear wheel to lockup.
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Wed Jun 05, 2019 4:25 pm quote
The first thing that happens when a belt starts to break up is it starts to shred Kevlar all over the place - I've actually found a failing belt in time *twice* by noticing yellow 'candy floss' dangling out of the rear vent in the transmission.

This Kevlar does NOT break easily - and it gets in between the clutch bell and the clutch plates and right into the innards of the clutch. A RRPITA to remove when this happens. The clutch can get locked absolutely solid, with the bell needing pullers and lots of swearing to get off.

There have been serious injuries caused by the rear wheel locking up like this. I seem to remember at least one such nasty incident happening to an MV member.
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Wed Jun 05, 2019 5:37 pm quote
Hold on, you’re talking about two different things.

A “locked clutch” isn’t a “locked rear wheel”.

Sorry, but I’m not even sure what you’re referring to by a “locked clutch”. Are you saying a broken belt can cause the clutch to not disengage? Or not to spin? Either way, it wouldn’t lock the rear wheel. Even a seized engine wouldn’t cause the rear wheel to lockup.
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Wed Jun 05, 2019 5:45 pm quote
Once the clutch bell gets seized solid to the rest of the clutch (and Kevlar is twined all around the clutch innards) the rest of the Kevlar gets pulled out, there's nothing left to support the rubber which gives way and balls up all around the variator and the clutch. Carnage inside, and possibly for the whole scoot and rider as well. If the whole clutch is jammed by belt detritus against the transmission case, then the rear wheel is jammed solid.
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Wed Jun 05, 2019 6:19 pm quote
Quote:
If the whole clutch is jammed by belt detritus against the transmission case, then the rear wheel is jammed solid.
Nope. When the clutch isn't spinning, it’s disengaged. So even in the highly unlikely event belt debris somehow managed to get jammed between the case in such a way as to keep the clutch bell from spinning, it would simply disengage the clutch. The rear wheel would still turn freely.

Believe it or not, Piaggio’s engineer’s actually thought about this. They anticipated that people may not change their belt as frequently as they should, and that many belts would break while people were riding. The transmission is designed so that a broken belt will not cause the rear wheel to lock up.
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Wed Jun 05, 2019 6:51 pm quote
In my case, the broken belt was tightly wrapped around the rear pulley setup and it still freely rotated, just not powered from the motor. I could push the scoot freely to get off the road safely once I came to a halt.

When you replace the belt, polish up the lower surface of the inside of the transmission case - the red area on the attachment pic...

My Vespa guru showed me how the OEM finish can be rough and the belt can actually slap against the casing slightly at speed (which we prevented with an additional washer to limit the squeeze.)

TransmissionCasing.png



Last edited by Fudmucker on Wed Jun 05, 2019 6:59 pm; edited 1 time in total
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Wed Jun 05, 2019 6:53 pm quote
SoCalGuy wrote:
Quote:
If the whole clutch is jammed by belt detritus against the transmission case, then the rear wheel is jammed solid.
Nope. When the clutch isn't spinning, it’s disengaged. So even in the highly unlikely event belt debris somehow managed to get jammed between the case in such a way as to keep the clutch bell from spinning, it would simply disengage the clutch. The rear wheel would still turn freely.

Believe it or not, Piaggio’s engineer’s actually thought about this. They anticipated that people may not change their belt as frequently as they should, and that many belts would break while people were riding. The transmission is designed so that a broken belt will not cause the rear wheel to lock up.
Yep, you win. Everyone this has ever happened to is a liar.
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Wed Jun 05, 2019 7:17 pm quote
I don't want to get into a spat, ladies, but from my own experience, I can't see how the belt would get between the clutch pulley edge and the casing to jam up...

When mine broke, the front pulley setup would have been at its largest diameter and the rear one at its smallest diameter - i.e. the belt is deepest at the rear between the pulley flanges. The belt broke and wrapped on itself, filling up the entire rear pulley, which rotated freely on the rear wheel bearing.

To lock up, that belt would have to snag between the transmission casing and the pulley, or between the pulley and the outside cover. I would NEVER say it could NEVER happen, but from mine and from the clearance I could see between the pulley and the casing, it would not be there. I could not see the clearance with the cover as this varies according to how the pulley moves and because it is behind the cover...

From the feel as I rode, the belt snapped inside and for a fraction of a second whirred until it had wrapped itself around the rear pulley and went completely silent.

Last edited by Fudmucker on Wed Jun 05, 2019 10:08 pm; edited 1 time in total
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Wed Jun 05, 2019 8:30 pm quote
Re: Much
Bill Dog wrote:
Forgive the highjack but the belt on a Kymco AK550 is supposed to last 48,000 miles.

Yeah, right.

Nill x
The bigger the engine the longer the belts last. Or more technically the bigger the variator the longer the belt last.

Vespa the same.
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Wed Jun 05, 2019 9:41 pm quote
My belt broke on my previous scooter. I was a greenhorn and I didn't know anything about scooters. It was very scary, because I rode in the city in big traffic, and suddenly it started to make strange and loudly noise. I was lucky, because I could stop safely. But sometimes it is not easy. I read on a forum about a guy, his belt broke the oil pump belt too, but he didn't realized. OK it is a 2t problem.
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Wed Jun 05, 2019 10:03 pm quote
Ask
Are you saying that it didn't happen ( because it did ) or that it can't happen -because it does.

Mine ended up spun and shredded into the variator. Fact.

I know as I was there when it happened.

Bill x
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Wed Jun 05, 2019 10:06 pm quote
Not sure who you are responding to...
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Wed Jun 05, 2019 10:53 pm quote
I've never been to America. Maybe it doesn't exist...
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Wed Jun 05, 2019 11:00 pm quote
Biff
It does.

I've seen The Rockford Files.

Bill x
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Thu Jun 06, 2019 12:19 am quote
Bueller wrote:
Yep, you win. Everyone this has ever happened to is a liar.
Reading through the thread, I don't see that anyone says it happened to them personally. People do say they read on the internet that it happened to someone else, or heard about it from a friend of a friend of the person it happened to, so technically no, the people it happened to aren't liars, because nobody is claiming it happened to them. When you think about how the transmissions work, it does seem farfetched, and highly unlikely, but not impossible that a broken belt could lock up a rear end. It's more likely that if you were buried in a corner and the belt broke, that could really throw off the handling.
I don't ride much, so I never had a belt break, except for one time I was using the wrong type of belt, one with a smooth top, on the GT200 because I wanted to see what would happen. It will break right away. . Other than that though, I've been fairly lucky. I use Malossi belts and they get changed at about 6-8K miles.
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Thu Jun 06, 2019 3:36 am quote
https://advrider.com/f/threads/wheel-lock-up-at-speed-with-mechanical-failure.817414/#post-26854294

https://advrider.com/f/threads/wheel-lock-up-at-speed-with-mechanical-failure.817414/#post-37291909

https://advrider.com/f/threads/wheel-lock-up-at-speed-with-mechanical-failure.817414/page-2#post-37300688

It can happen. It’s not all that common, but if the pieces jam the clutch bell badly enough you will get a lockup.

One thing I learned during the three decades I worked as a master auto tech, shop foreman, and almost 10 years with Harley - just when I think it’s not possible, someone proves it is!
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Thu Jun 06, 2019 4:10 am quote
It's not hard to see how a broken belt could lock up the rear wheel. The clutch bell is directly coupled to the wheel, through the final gears. It's also completely exposed in the transmission case; there's no shield or anything around it. So chunks and fibers from a broken belt could get jammed between the bell and the case, therefore locking up the rear wheel.

No, I've never had this happen to me and the two times I've seen belts break they didn't lock up the wheel, but I can see how it could happen.
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Thu Jun 06, 2019 6:47 am quote
Gif
It happened to me personally and I claim my $20.

Bill x
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Thu Jun 06, 2019 7:26 am quote
SoCalGuy wrote:
Quote:
If the whole clutch is jammed by belt detritus against the transmission case, then the rear wheel is jammed solid.
Nope. When the clutch isn't spinning, it’s disengaged. So even in the highly unlikely event belt debris somehow managed to get jammed between the case in such a way as to keep the clutch bell from spinning, it would simply disengage the clutch. The rear wheel would still turn freely.

Believe it or not, Piaggio’s engineer’s actually thought about this. They anticipated that people may not change their belt as frequently as they should, and that many belts would break while people were riding. The transmission is designed so that a broken belt will not cause the rear wheel to lock up.
So the clutch holding tool that we use to help undo the clutch nut is a mythical object? The clutch is disengaged after all...
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Thu Jun 06, 2019 9:59 am quote
Bueller wrote:
https://advrider.com/f/threads/wheel-lock-up-at-speed-with-mechanical-failure.817414/#post-26854294

https://advrider.com/f/threads/wheel-lock-up-at-speed-with-mechanical-failure.817414/#post-37291909

https://advrider.com/f/threads/wheel-lock-up-at-speed-with-mechanical-failure.817414/page-2#post-37300688

It can happen. It’s not all that common, but if the pieces jam the clutch bell badly enough you will get a lockup.

One thing I learned during the three decades I worked as a master auto tech, shop foreman, and almost 10 years with Harley - just when I think it’s not possible, someone proves it is!
Lots of wheel lockups and broken belts.
Here's a quote from one:
" The very first time I experienced a belt break, the rear locked up. Luckily it was a no-traffic rural road, and on a 49cc scoot @ 30 mph.

And yes - it definitely messed up (bent) the driven sheave/pulley, which required replacement afterwards."
So the belt broke the clutch? Or did the clutch fail, lock up and break the belt?
Given the difference in composition of the two items, the description of the vehicle as 49cc Scoot, which usually means Chinese, and the things I've seen Chinese clutches do, I'm inclined to think the clutch broke, caused the rear wheel to lock up and broke the belt.
If you read enough of these, you will see a couple of patterns emerge. The belts that broke, without any other component damage, didn't lock up the wheel. The times when the wheel did lock up, there was usually other damage in the transmission as well. So, which one led to the other?
Also, the ones that have the most likelihood of damage are often posted by people who start or add to threads about installing cheap parts, having this happen to cheap (Chinese) scooters, and/or someone doing their own work, usually with the cheapest parts they could find.
If you have a good scooter, with good parts that are in working order, and everything has been put together correctly, the odds are significant that a broken belt will not lock up the rear wheel.
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