Modern Vespa

I was calibrating my speedometer after changing the timing wheel. I felt the bike "slip" then there was no response from wheel when turning the throttle. I was planning on pulling the belt cover this weekend but thought I would ask the group if this had happened to anyone.

Sounds like you broke a belt.

Open it up and see what you've got going on.

Without looking that was my first thought. The bike only had 540 miles on it when I purchased it 2/2022. I just thought that was early for the belt to break. It has 3600 miles on it now.

Sometimes it's not the mileage it's the age.

Hope it's just the belt, anything else would be real real bad.

Make sure you really search with a good light for any strands of the belt if it broke. It can easily take out an oil seal in the gearbox.

Well, I finally got weather and time on my side. I pulled the covers. It is not the belt. The belt looks brand new. Once I saw that I just buttoned it back up. Fortunately I have a great Vespa dealer in Richmond VA. Their mechanics are really good. It is probably going to put a big dent in my wallet.

Thanks for all your inputs.

I would think this would be a warranty problem, not your problem.

So not a broken belt and the rear wheel rotates freely when it is on the center stand I am gathering.

You might as well keep looking as long as you have the transmission cover off. I lost engine engagement once when the aluminum variator teeth sheared off - an intentional failure point so the crankshaft splines weren't damaged. I'd driven about 1000 miles with a spacing washer in the wrong place on the variator assembly.

That would be great if it is a warranty problem, but the bike is a 2020. As for the remark about the wheel spinning freely, yes it does.

Juan, I put it all back together when I saw that the belt was ok. It is obviously something internal.

the belt is internal

I my DIY thinking, anything behind the variator/belt is internal. I don't feel safe going there.

so, just so I'm understanding this correctly: you pulled the cover off and saw that the belt was still in one piece.

from there you didn't inspect or check anything else?

the motor starts, runs, just no power to the rear wheel?

so, just so I'm understanding this correctly: you pulled the cover off and saw that the belt was still in one piece. [yes, the belt looked perfect, no visable wear at all]

from there you didn't inspect or check anything else? I looked to see if the belt was jammed (no). I pulled the clutch drum and looked at the Centrifugal clutch assembly but could see nothing awry.

the motor starts, runs, just no power to the rear wheel?
Actually , I did not again atempt to start the motor. It was working fine when I turned it off, just no engagement of the wheel.

I just started the motor. It ran fine. The real wheel does not move like it normally does. One other symptom, I had just filled up the oil prior to my last ride (when I was setting my speedometer). There is no oil visible in the sight glass. I did notice when I was pulling the covers today that there was oil in places where it should not be. Not puddles or anything but spots of oil, even on the rear tire.

hm. interesting. without seeing a pic I'd guess that maybe the front 1/2 pulley is stripped on the crank. hopefully it didn't go on too long and strip the crank where the back plate of the variator rides.

besides a broken input or axle shaft or something awry in the gearbox (which would make a horrible sound and likely not roll) I'm guessing that it's 1/2 pulley or vario. hope for the 1/2 pulley, it's cheap and easy.

if you're mechanical in the slightest, it's something you could do yourself. worst case you could take it all apart and know what you're up against going into the shop.

When you filled up the oil, did you fill it up to the top of the sight glass with the scooter on the centerstand? Where is the oil level in the sight glass now with the engine OFF and the scooter on the centerstand?

I would have started the engine while I had the cover off, revved it up a bit, and observed what was going on under the cover. Like, were the front and rear pulleys turning? Did the front pulley close and the rear pulley open as engine speed increased? If they did, and the front pulley was tight on the crankshaft, Then there are still two possible problems. It could be in the rear pulley/clutch assembly, such as the clutch shoes not engaging, the clutch bell being loose, or broken pins in the rear driven assembly. If everything there is ok, the only thing left is the final drive gearbox. Not sure I understand what you mean when you say you felt the bike "slip". You mean it felt like pulling in the clutch on a manual transmission bike? Did it make any noise when it slipped? Have you changed or checked the oil in the final drive? Do you actually see an oil leak, or just oil where it is not supposed to be? Could you have overfilled the engine with oil? Sometimes that will cause oil to be blown out through the airbox. Pull the airbox cover and look in there for oil. With the cover off and the engine off, spin the rear wheel by hand. Does the rear pulley turn? If it does, hold it with your hand and turn the rear wheel? Does it still turn?

There is a broken connection somewhere between the crankshaft and the rear wheel. It should not be hard to determine where it is. Fixing it may or may not be a do it yourself job if you are not a mechanic or mechanically inclined. The worst thing it could be is stripped splines on the crankshaft, the next worst thing is a bad final drive. That would not be cheap, but at least it does not require a complete engine removal and teardown.

okay. back up. so you were doing the tone wheel and then the wheel thing happened? so you had the muffler/swing arm and such off?

now there is currently no oil visible in the sight glass even though you previously topped it up? and there is a ton of oil in the transmission case and on the tire?

when you say the wheel doesn't move like it normally does, can you describe it? is it on the center stand or on the ground when that happens? do you have any warning lights in the dash?

pictures would probably tell a better story.

this is bad advice. unless you are incredibly careful you risk damaging other components and possibly hurting yourself.

No components in there to damage as long as you don't touch anything with the engine running. Same thing with hurting yourself. Keep your hands and any loose clothes away from the pulleys and belt while the engine is running.

This is not a Vespa, but all variators work pretty much the same. Here is what you can expect to see running it with the cover off. Most Vespas have an idler pulley between the front and rear pulley, but it doesn't change how things work. Start around 12:50. Notice how the rear clutch bell starts turning when the engine is revved, and how the front and rear pulleys open and close. That's what changes the gear ratio. Obviously don't get your hands, clothes, hair, or anything else close to the moving parts.

Where is the clutch nut when all this is going on?

Wow, So much advice in a very short period. I will try and answer all the questions.
1. When you filled up the oil, did you fill it up to the top of the sight glass with the scooter on the centerstand? No, I filled it where I could see about 1/4 in in the glass. I ran the motor, let it settle, then added 125 ML. That took the oil up just above the 1/2 way mark in the sight glass.

Where is the oil level in the sight glass now with the engine OFF and the scooter on the centerstand? No oil visible in the sight glass

Not sure I understand what you mean when you say you felt the bike "slip". You mean it felt like pulling in the clutch on a manual transmission bike? No, the sensation was like if the chain comes off a bicycle when pedaling.

Did it make any noise when it slipped? No noise that I remember.

Have you changed or checked the oil in the final drive? No

Do you actually see an oil leak, or just oil where it is not supposed to be? I did not see a leak.

Could you have overfilled the engine with oil? NO
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okay. back up. so you were doing the tone wheel and then the wheel thing happened? so you had the muffler/swing arm and such off? Yes, to change out the tone wheel.

now there is currently no oil visible in the sight glass even though you previously topped it up? and there is a ton of oil in the transmission case and on the tire? I didn't see a "ton" of oil anywhere. Just visible oil inside the area behind the engine cover.

When you say the wheel doesn't move like it normally does, can you describe it? When normally on the centerstand and the engine is idling, the wheel moves very slowly. like I would expect a motor with a centrifigal clutch to do. Now it doesn't move at all.

Do you have any warning lights in the dash? No

pictures would probably tell a better story.

Where is the clutch nut when all this is going on? The clutch nut and washer were set aside while the cover was off.

Well, Now I am confused. I just went out, cranked the motor. The wheel is turning normally. No warning lights.... However, there is still no oil visible in the sight glass.
I tried taking a video, it was terrible.

Oh, when the engine was running just now I turned the throttle, engine sped up and so did the rear wheel. I really hate problems that just disappear.

"Where is the oil level in the sight glass now with the engine OFF and the scooter on the centerstand? No oil visible in the sight glass"

This part is scary. I definitely wouldn't run the engine like that. My GT200 has a dipstick, and I keep the oil level even with the top mark with the scooter on the centerstand. I have bikes with oil sight glasses, and I keep the oil level just even with the top of the sight glass. It's fine if you can just see a tiny bubble at the top of the sight glass, but the oil level needs to be very close to the top. I don't know about the GTS300, but the GT200 holds just a hair over one quart of oil, and it will burn some when being ridden for long periods at full throttle. When on a long ride, I check the oil when I stop for gas, after the engine has been off for a few minutes. With so little oil you risk running out of oil and destroying the engine, so I keep it as full as possible without overfilling it.

"When you say the wheel doesn't move like it normally does, can you describe it? When normally on the centerstand and the engine is idling, the wheel moves very slowly. like I would expect a motor with a centrifigal clutch to do. Now it doesn't move at all"

It's normal for the rear wheel to turn slowly at idle, depending on how high the idle is set. On an EFI scooter the idle shouldn't be adjustable. I'm assuming it doesn't move even when you rev the motor?

"Where is the clutch nut when all this is going on? The clutch nut and washer were set aside while the cover was off"

This wouldn't make any difference if you did not run the engine with the cover off. Obviously the clutch bell has to be in place for the centrifugal clutch to work. I'm assuming the clutch bell was in place when you put the CVT cover back on?

Ok, first I would put more oil in the engine, fill it up at least very close to the top of the sight glass. Then pull the CVT cover off again, and start checking things. Is the nut on the front pulley tight? Turn the front pulley by hand. Does it feel even slightly loose? Put a wrench or socket on the front pulley nut and turn it counterclockwise. The front pulley is attached directly to the crankshaft, so turning it with a wrench should turn the engine over.

If that is ok, go to the rear pulley and turn the clutch bell by hand. There should be some resistance, and the rear wheel should turn. If the rear wheel does not turn when you turn the clutch bell, remove the clutch bell and turn the splined shaft by hand. That shaft is part of the geared final drive. If the rear wheel does not turn when you turn the shaft, then the problem is in the final drive gearcase. I've never had one apart, so I don't know exactly what's in there, other than gears. If the wheel does not turn when you turn the rear shaft, the gears are not meshing. That would not be good, but it's a lot better than stripped splines on the crankshaft.

As far as your oil level goes, what is the level showing on the dipstick? THe wheel not moving while on the centerstand may have something to do with the ASR traction control.

All that for nothing? Oh well. DO NOT run the engine until there is oil in the sight glass. You still need to find out what happened to the oil, unless you made a mistake when you checked it before. Brand new oil can be so clear it can look like there is no oil there. You need to make ABSOLUTELY SURE there is oil in the engine. Then you need to find out where the oil in the CVT case came from. There are two oil seals in the CVT case. One is around the crankshaft, behind the front pulley. That's for engine oil. The other is around the final drive gear case shaft, behind the rear pulley. That's for gear oil. The only other thing I can think of is that oil blew out through the breather and into the airbox, and dripped down. Are you SURE there is no oil in the sight glass, or could the oil level be above the top of the sight glass? You also need to change the gear oil in the final drive. That way you will know what's in there, and how much.

I have no idea how traction control works.

znomit's question about the clutch nut was in the context of someone above mentioning starting the engine with the cover off. 1. you'd need the nut on the clutch shaft to stop it flying off and hitting you in the face. 2. the shaft normally would have the support of the transmission cover to keep it in place while the force of the belt pulls on it. Just don't do this

Last edited by SteelBytes on Sun, 19 Mar 2023 22:27:26 +0000; edited 1 time

the rear wheel will turn regardless of asr on/off. if it's on and you accelerate gently it should make no difference. but if you really wanted to play with the throttle then the asr will cause the ecu to cut some power* making the engine not sound normal. it's best to just turn off the asr with the switch on the handlebars

* iirc it cuts some of the spark. imagine only doing every second spark or something like that.

I'm curious. The speedo is not adjustable. Did you maybe mean calibrating the ASR as described in the manual which doesn't affect the speedo?

I'm curious. The speedo is not adjustable. Did you maybe mean calibrating the ASR as described in the manual which doesn't affect the speedo?

Yes, I had replaced the timing wheel which then requires a recalibrating the ASR.