Modern Vespa

I noticed a graunching noise on take-off on my GTS several weeks ago; coming from the left side behind me (ok, so I'm not mechanically inclined).

I had the belt and rollers replaced at 14k miles. 1k miles later the noise started. Took it back to the shop and they did notice it immediately when they started a test drive.

They took the transmission apart, checked all rollers but found nothing. The mechanic went very easy on the labor charge (I was also getting new tires, so I was pleasantly surprised with the bill - thanks Rockridge Two Wheels).

It was quiet for a couple of weeks and now it's started again. I now have $16.5k miles on it.

Any clues as to what it might be? I don't want to start spending mega $$$$ on this.

Belt dust causing the clutch to slip. I'd put money on it.

You can have it remedied by taking apart the transmission and cleaning everything out, but belt dust will accumulate there again in short order. Easier solution is to take it out for a long, spirited ride and get the transmission to blow the dust out of itself for you.

A sprited ride. That's the ticket! I think I'll do just that.

Thanks.

There are two reasons for this, the first is as Jess said, dust build-up in the transmission and slipping of the belt.

The second also concerns the clutch. At 16500 miles you could have a worn clutch and the friction material at the leading edge of the three clutch shoes could be worn down, causing the metal nub at the front of the shoe to contact the clutch bell and cause the judder.

If a good run doesn't sort it out then take off the transmission cover (clutch nut and 8mm bolts) and use emery paper to deglaze the clutch shoes and also the bell. Have a look at the leading edge of these shoes and if you can see any worn metal, your clutch is on its way out.

You can remedy this temporarily as I did on an ET4 with a dremel and the sanding drum to remove the offending metalwork!

I suspect yours is the first problem as it seemed to clear up for a while when they last opened and examined the transmission.

Same here, and it comes and goes without external interaction.

Can you confirm this to be true for you too: the noise only happens when you take off slowly. At a WOT start, the clutch grips as it should, with none of that noise.
It may also be more prone to happen with a warm clutch.

My clutch liners are definitely still good, with several mm between them and metal, so in my case it can't be a worn clutch. It could be glazed-over, I'll check that next time when I'm in there to replace the variator.

I've had that occurrence for at least the last 6 to 8K miles, on and off (and mostly off). I'm not worried anymore, just annoyed, when it happens.

I thought my clutch friction material had plenty of meat as well. That is until I looked more closely. The material doesn't wear evenly, the edge nearest the pivot point will hit the bell first as the clutch engages, so will wear more rapidly than the trailing edge. There is also a little bit of raised metal where the leading edge attaches to the pivot point, which can hit the clutch bell.

Glazing and dust build up are more likely to be the problem.

The graunching noise or strangled sea-lion noise is a well known design issue for the 250 engine. It frequently happens as the clutch bites when the clutch is hot. It shouldn't affect the working of the clutch and is not dangerous. It is said to be caused by a build up of dust or the clutch plates getting shiny. I had it on my 250 MP3 and it is very annoying, because it is so loud. Some people say it will go away when the mileage rises and cleaning the dust out may help. I never solved it but moved onto a Vespa 125 LX for other reasons.

+1 I had that same issue after a belt change and it went away, but I also sprayed break cleaner in the clutch area and they helped a little.