Modern Vespa

Ok, so just a quickie here. Had a guy come to me yesterday with a problem he has been experiencing over the last week or so. He had replaced his belt and rollers, ramp plate guides too. Yet his clutch nut on the gearbox input shaft keeps coming loose. He's been lucky as he realised what the issue was when he began to hear and feel something was wrong. His variator nut was fine, but the clutch retaining nut on it's shaft was loosening.

First question I asked was: ok so what torque are you using? His reply surprised me. He said about 45nm. That's the correct torque he said. I said "no it isn't". He said "yes it is, it's in the book!"

Ok so we both checked and I proved his figure was wrong. As many of you know it's actually 54-60nm. That's why his nut keeps coming loose!

So how did he make this mistake. Well, it's very easy to get it wrong if you are not fully aware of how the bike goes together and how the parts are labelled. In the workshop manual they describe a "clutch nut" and the "Driven Pulley" nut. The clutch nut is the large nut holding the whole clutch assembly together (45-50nm), and the Driven Pulley nut is the one on the end of the clutch gearbox input shaft (54-60nm).

He simply misread and or didn't fully understand the components he was reading about. He also failed to use new Belfield washer and nut on the variator and a new nut on the clutch shaft. That won't help either. If you always use new nuts (cost is peanuts) and a new Belfied washer on the variator there is no need for any threadlock (Piaggio don't recommend it) and they won't come undone. That is unless someone has overtorqued them repeatedly in the past and stretched the threads. This can happen when someone uses thread lock of some kind. Non engineering types often don't realise you must normally (but not always dependant upon application and thread lock compound being used) reduce the amount of torque applied to a bolt or nut when using a thread lock compound to avoid overstressing the nut or bolt threads. There are usually specific instructions from manufacturers on what to do if you use a thread lock compound. Stick to their instructions religiously. I repeat though, Piaggio don't recommend using a thread lock compound on these components.

This is not the first time I've come across someone confused about those actual torque figures either. It depends on where you read the torque values from as to how confusing it is. Folks on the whole tend to look for the "Clutch Nut Torque Value". Well, there it is 45-50nm!!! Except it's often not the one they want and they go on to experience the delights of a loose clutch shaft nut. As we've seen on here over the years, it's not a unique experience because of this misreading of values!

I can see how confusion can arise, so I've added this image. Is this correct Ian?

Hi Andrew,

Yes that's perfect! Excellent photo editing skills I see....

Since I have 3 scooters still and always lend out a service manual and never have it when I need it, I found a simple solution. After cleaning all the parts I wrote the torque N-m on the part with a Sharpie. Or will scribe it on the part. I can now pull any transmission apart without the service manual because the torques are already noted. And yes, I know how that person mixed up the torques. The Piaggio manuals are rather confusing. Best labeled manuals are Honda, worse so far are Suzuki.

Yes sc00ter, I agree! Good idea about scribing the values to the nuts or whatever.

Thanks for the clarification, Stromrider. I would probably have used the wrong value!
Cheers, Jim.

Nah Jim...you're too smart!

when i started down the long road to becoming a mechanic an old timer at the shop gave me a word of advice (well, several did but most are not to be repeated in uhhh.... mixed company...)

anyway, he told me to never memorize torque values. it was too easy to get them mixed up or forget which was which or just flat ass get it wrong because you "thought" you had remembered it.

so i always turn to my volumes of repair manuals. granted, they've been heavily annotated over the years with my chicken scratch on the margins and highlighter here and there, but they've yet to fail me in any way.

there's only two that i remember always though. vespa crank nut and vespa clutch nut. with how many i've done it's just imprinted into my brain.

everything else, to the books!

-g

I changed the belt on one of my GTs Sunday morning.

Just to be certain before tightening down the driving (variator) and driven (clutch) Nuts, I went to the Wiki here on MV and found the service manual in Wotmeworry"

It always feels better to double check on the important ones.

Bill

greasy, WLeuthold...very good advice. And of course, the other point is that sometimes manufacturers may change a torque value on something, so keeping up to date with stuff is always a good idea. Although I'm not aware of Piaggio doing this on any of our Vespas recently.

Like greasy I have far too many manuals, far too much computer software (the modern way of doing things...lol) listing all this stuff to follow. Like you guys though, it's really important to check values each time before doing the job.