Modern Vespa

As some of you may know I have been planning to change the belt and rollers on my Vespa ET4 50 for some time now. Today I finally got round to it though it took a bit of work I got it done all seemed fine until it came to testing it the starter motor just locked up each time I tried it . The engine will turn over with the kick start but it is a bit stiff compared to normal. Any ideas? I'll open it up again tomorrow to see if anything is out of place.

Also the rollers I took out used to be orange the ones I fitted are black any difference (apart from colour)?

You may have pinched the belt between the variator halves, which would prevent you from completely tightening them together, subsequently causing the outer half to rub against the transition housing when re-installed.

It is tightened up as much as it was before but I may have trapped the belt somewhere. Would this prevent it starting?

Yes.

You have to 'untwist' the clutch to make sure the belt is well stuffed down inside the driven pulley halves. Then you can do the variator up just fine.

Ok I'll give that a go and let you know how it goes. Thanks

check out this wiki article: https://modernvespa.com/forum/wiki-gts-300-jcosta-installation

the instructions are for a GTS, but if you scroll down you'll see two pictures showing how to get the belt properly down inside the halves of the driven pulley, and what it looks like when it's correctly seated. the principle is identical for your scooter. make sure you orient the belt in the right direction too

Nice one! Thanks genie I'll have a look in a bit hopefully that'll sort it.

NOOO!! just opened up the side casing to find the belt fitted backwards I completely forgot about that yesterday. Apart from that though everything seems fine however the belt is alot harder to turn, I'm thinking maybe I overtightend the nut on the variator would it be OK just to back it off a bit? Here are some pics let me kow what you think? Thanks.

No, do not just loosen the nut. You need to get the belt further down in the clutch pulley groove and further out of the drive pulley so it's loose when you tighten the nut. Once the nut is tight you should still be about to move the belt around in the front pulley. Does that make sense?

Wayne B

NO!!! NO!!! NO!!! NO!!!

If you loosen the variator nut you will absolutely, without a doubt ruin your bike--the crankshaft will be damaged and you will require a complete engine rebuild.

As others have noted, you have pinched the belt in the variator on assembly. You must remove the nut, remove the outer variator half, and remove the driven pulley.

You must make sure the belt is deep inside the driven pulleys in order to have enough slack to install the outer variator half. This would be a good time to make sure the belt is oriented correctly (arrows point in direction of travel).

Put the driven pulley, clutch side down. Push hard on the lower pulley and shove the belt as deeply into the gap as possible. This is easier with two people--one separates the pulleys while the other shoves the belt in deep.

Make sure the belt doesn't slip out as you reinstall the driven pulley.

Now you have plenty of slack for the outer variator half to go on properly. On the GT and GTS there is a washer that goes on the shaft before the outer variator--I'm not sure about the LX, but I'm guessing yes.

Install the outer variator half. Install the two outer washers (big first, then small) and tighten the nut to the correct torque. This is important, so use a torque wrench.

Now everything should move nice and easy (accounting for engine compression, of course).

It is a good idea to mark the position of the variator nut relative to the shaft with paint or a Sharpie®, so you can be sure it doesn't move after you've run the bike a while.

Good luck,

P.

If I may add that the nut should be replaced because it is a "one time stretch" fastener. Especially since the OP admitted to over tightening the nut and that is evidenced by the distorted hex in the pictures.

I have removed the nut completely to switch the belt round but I'll get a new one before re-fitting. Is the driven pulley on the left? I'm not sure I overtightened the nut that was just a suggestion as to why it wouldn't start. What is the correct torque for the crank nut? The sharpie is a great idea which I will definatly use when I next reassemble it. How can I seat the belt deep in the pulleys but not pinch it? There wasn't a washer between the variator halves when I opened it.

Also is it completly necessary to remove the clutch bell aswell as we managed to fit the belt in quite well with it fitted before surely we can just ease the belt up or down as necessary? Sorry I know I have asked alot of question I just want to get this sorted so I can enjoy the good weather this turns out to be far more difficult than I expected. Thanks for all your help so far.

the drive pulley is the one on the left, the driven pulley is the one on the right. the clutch and driven pulley is a single assembly that lies beneath the clutch bell. you'll notice the clutch/pulley assembly has two round plates which can be pulled apart with a bit of effort - you may have to twist them a bit. you want to seat the belt as deep as you can between these two halves by pulling them apart and making sure the belt is down as far as it will go - not just looped around the two plates. this is easier if you've got somebody to pull the clutch plates apart for you while you seat the belt

you also need to make sure that you've pushed the drive pulley assembly as far back against the crankshaft spline as you can when you put it back on. this is a bit fiddly and may require bit of wiggling around (of the assembly, not you). check out this thread for what can happen if you don't: FUBAR Final. Pictures of How not to work on your CVT.

Right thanks again genie I think I've got it now. So i have to pull the two plates of the clutch (which are on the right held together with the spring) apart so I can then push the belt in as far as possible. This will then give me enough slack on the left at the drive pulley to move the belt away from the center of the two variator halves so I can seat them tightly together and well onto the crank shaft then using a new crank nut tighten it all on using a torque wrench (Still unsure how tight it should be) I will post up some more pics before i close it all up to make sure I've got it right third time lucky hopefully . This time I will photograph every stage very clearly and post them up so nobody else encounters similar problems.

P.S I will mark where the nut is on the crankshaft with a sharpie then check up on it in a few days or after a few miles to make sure the nut hasn't backed off. Great idea Paul G.

yup that's about right though i think it is the clutch nut that needs replacing each time.

for the correct torque you'll need to go to the manual - which i believe you will find here, thanks to jimc http://www.wotmeworry.org.uk/manuals/ET4/

Both of those nuts in the pictures are the "one-time use only" type, Genie. I'd worry more about the variator nut, though. I've never heard about a clutch nut backing off.

ah, cheers. how does one identify a 'single use only' nut? is there anything specific about the nut itself or is it just a matter of where it's located?

i've been using loctite

The single-use nuts have a cupped washer attached to their underside that flattens as the nut is tightened to the proper torque, theoretically locking it on. Once the washer has deformed the first time, it won't provide the same locking force on subsequent uses. In actuality, blue Loctite would probably serve as well.

The service manual should identify which nuts are one time stretch.