jumping out of first gear

[dickie]

I've just got my engine running and everything seems well except first gear.

Background is:

Fully rebuilt engine/gearbox following sticky's rebuild procedure as best as I could (first time for me)
New components in gear box are: layshaft, selector, seector pawls, spring and balls, first gear, bearings, shims, clutch.

I can get it into first gear and pull away, but unless I hold the shifter back it jumps out of gear into neutral. Also, the "clunk" into first gear is less clunky than all other gears; it feels like it sort of "flops" into first rather.

The cables aren't tight, so it's not that.

Unfortunately, I think there are two options here:

1. Leave it alone and hope that the new components will bed in nicely
2. Strip gearbox and have a look for something.

My feeling is that option 2 is the correct one, but I really want to be wrong. Also if I do strip it, is there something in particular to look for?

thanks

[Storkfoot]

#2_ check endplate is fitted down right (ie tight enough) and that shim tolerance ok. Check sliding dog ( is it original, italian remade or SIL ?) and that correct spring is fitted between the ball bearings

[dickie]

#2 check endplate is fitted down right (ie right enough) and that shim tolerance ok. Check sliding dog ( is it original, italian remade or SIL ?)

Obviously shim plate WAS tight enough but might not be now?

Shim tolerance was on the tight end of the recommended scale.

I can't remember where I got the sliding dog from but I'll find the receipt and report back; are there known issues with some of them?

How do I know if it's the correct spring or not? I bought it from sr.

[Storkfoot]

If you bought the selecter spring from SR it should be ok. I use there's too. In my experience, Indian sliding dogs can be of variable quality although problems with the sliding dogs, again in my experience, appear to manifest themselves in difficult gear changes.

If your cables are fitted correctly, not too loose or too tight and correctly placed ie neutral engages at the correct place on your handlebars, then a loose endplate would result in jumping it of gear. I had the same occur to me.

[dickie]

Yes, the sliding dog needed quite a bit of fettling to allow it to slide nicely through the layshaf.

My cables are very slack as I thought by making them slack I could eliminate them from the issue.

I'd be surprised if my plate is loose as I've only ridden about 500 metres up and down the street (with no helmet, so I got a ticking-off from the copper who lives opposite me :$ ).

[Wack]

Firstly check the casing swivel can move forward enough to select first without touching anything and the post is the correct way around. I've seen gearbox selectors where the internal notches are machined in the wrong positions, ID'd by a nice machined finish all over. I always use SIL selectors and never had a problem with them. Your best bet would be to strip endplate off then manually select each gear, noting where the selector dogs engage in each gear and that there is clearance between the gears when in neutral . Usually when the selector is in first the dogs protrude just past the layshaft, also check the first gear internal faces are not rounded.

[dickie]

Gents, thanks for your help. But no one managed to guess how simple the fix was.

I had tucked the free ends of the gear cables back into the gaps between the trunnions and the swivel. it looked like a lovely neat and tidy job.

However, it makes your lambretta jump out of first gear.

I feel rather foolish but pleased it was such a simple job. I've never had a lambretta that worked before so I can only compare it to the vespas I owned in my youth and I can safely say that the gearshift is much slicker on this.

Well chuffed.

[Digger]