Modern Vespa

It's probably apparent already that I don't find working on Vespa engines easy
And I'm sure there's a simple explanation BUT this is really bugging me. When the gear selector rod is tight in the cruciform, the cruciform does not go to the top of the layshaft(FIRST PIC) & when it is slightly loose it goes to the top(second pic) Is this Correct?
The layshaft in the pics is not the one I'm using in my build as the thread is knackered and the cruciform is stuck in the rod but the new one I bought does the same thing.
So to sum up... should the cruciform stop before the top or not?

Should go all the way to the top…

The only thing stopping it are the spacer and circlip (when the gears are all placed on the shaft).

Sounds like your output shaft isn't straight no more or there's something obstructing it on the inside (metal nick or a warp?)…

While it should be free all the way up and down, picture 1 looks like it would work. It's less than ideal. You can see wear marks on the axle where first gear spins. Looks like the cross gets to those wear points.

Since it is binding, I'd replace the spindle and make sure it will move all the way! If I was desperate and only had Picture 1 as an option, I'd do it knowing I'd have to re-do it asap.

Thanks for that. The thing is it does it on the old one & new one I bought today. With the rod tight in the cruciform it will only go 3/4 or so all the way up but loosen it off slightly and it will slide freely to the top. I can't get my head round it at all

If both crosses get the same result, I'd say your spindle is off. New replacements arent that much.

This is the new layshaft(just took it out again) It has a new Rod & cruciform in it. Fully tightened & this is as far up as it goes before jamming

Ok not good. You need to exchange those for something that moves easier. Where did you buy from? Hopefully a shop nearby.

I'm guessing this area in the photo is the problem, if it's not straight you'll bind as the rod moves out…

I think the cruciform moves to the top when it's loose, because theres enough play for it to move…

Sounds like you might have to destroy the old rod and cruciform to double check, unless you can get your hands on another shaft to check too.

Luckily (or sometimes unluckily) I live near Beedspeed so that's not a problem. I just can't understand why it only happens when the cruciform & Rod are screwed together. Separately they slide up & down just fine. It's as if joining them throughs them out of true. But doesn't explain it happening with different rods & cruciforms. Or that when in certain places on the thread they slide fine

Thanks, yes I'll try and get the rod & cruciform out of original layshaft... that will be fun lol.

Can't really see from the pics. Is the washer in there?? Does the indent face the selector rod??

Hi Safis, yes washer is on the rod and right way round

I've made a video which hopefully will show the problem a bit better.

https://youtube.com/shorts/g6s5rdu_INs?feature=share

The play in the threads will go away when it's tightened.

Hi there, It's not the play in the threads. When it's as tight as it should be it won't slide up the layshaft as far as it should so gear change will be problematic

Maybe the threads in the cruciform were not machined completely straight or centered.

Yeah that did cross my mind but I've tried it with the old cruciform and it's the same. Thing is It does the same on the old driveshaft too which is really confusing.