Scooterotica

So, you've shimmed it with just the gears(and shim under endplate needle bearing) on the layshaft, no main shaft and all was well.
When you put the mainshaft in, put the endplate on, there is a tight spot, but only when you install the crown wheel and spider.
A. Make sure the crown wheel and spider are compatable, ie they don't bind up when mated together, but not installed. Could be bad crownwheel/spider brearings.
B. Check to make absolutely sure that there is no dirt between any of the teeth on the gears on the layshaft and mainshaft.
C. Or as Mark said, try another endplate.
As the problem only occurs when crownwheel/spider are mated, that's the best place- to start looking.
Apparently, cases and endplates are a matched pair, I seem to have read somewhere. Can't remember where I heard it . Also apparently, there are some people who seperate cases and endplates and stack them on the shelf seperately

Try tapping all around the end plate with a mallet before you tighten up the nuts. Make sure its turns before you tighten.
If this dosnt work you have the wrong endplate.

take of crownwheel and spider ,put the spider and bush into the crownwheel ,turn over and check that the center of the spider is higher than the back edge of the crown wheel ,if not it will lock up when tightened

Caballeros.... (Gents...) I much apreciate your help!! Problem is solved!!(finally!!!) It so happened that stupid me, didn't put attention that the seeger ring on the endplatewas rubbing with the spacer... some careless spaniard that wasn't me, hit the lip with a hammer or sort of a hammer and damaged the lip a bit. So it does not close up all the way, it sticks a little on one end, hence rubbing with the spacer, hence not turning after half a turn... So... .BODGE BODGE BODGE! Kinda like Sabina's song from the 80's.. I took the grinder off and ground off a thou of the diameter of the spacer.. PROBLEM SORTED!!!!!!! turns fantastically well

i think you meant Sabrina...and not maybe sabina...
http://www.youtube.com/watch?v=eiuHdUkuRi0

You got it Sean!!.... well sing along... BODGE BODGE BODGE!! I'm fixing my lambretta! Bodge bodge bodge! The freggin' stud has broken! Bodge bodge bodge!!

.....

I know Lopez... I sing awfully...