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4th gear jumping out

Technical help for Series one, two and three Lambrettas. Models include the Li, Li Special, TV, SX, GP, Serveta and API/SIL models

4th gear jumping out

Postby Topgearskin » Tue May 03, 2022 10:45 am

Well, this has got me stumped.
Std GP200 engine on a Spanish case. All gear select with no issues, but 4th jumps out and won't stay selected.
Cables all seem okay- not too tight, not too slack
Selector arm at 90 degrees in 2nd and has about 3mm gap between the tip and the shock support in 4th.
Selector swivel arm isn't fouling on the nuts
Headset end is fine, no issues,

Pulled the gearbox out (end plate float checked and that's ok- all nuts torqued correctly)
No shavings or metal dust in the oil
No marks on the casings to point to wishbone rubbing
Wishbone held in with a dome cap nut, no wear on that
4th gear meshes with the Xmas tree perfectly, and the gear itself looks great, no wear or missing teeth
Swapped the sliding dog (it was a new SIL item). Replaced it with an Italian one. Problem seemed to go away, then 40 miles later its back and worse.
Pulled the gearbox out again and double checked all of the above. No signs of an issue.

So before I pull it apart for the 3rd time.....

Any ideas?
Topgearskin
 
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Re: 4th gear jumping out

Postby Warkton Tornado No.1 » Tue May 03, 2022 11:46 am

Presuming that all of the many components in the whole process of gear selection usually susceptible to wear have been checked, then it could be the gear drive faces, the cursor drive faces (dogs) - despite it being changed - worn bushes in the case (or the selector shaft that fits within carrying the wishbone). The screws that hold on the components to the top of the case & cables can give issues, such as 'springy' outers. A bent shaft @ the headset end can also be overlooked as can any play @ that end.

Personally, although they are not popular due to Webbo's comments, I prefer the two piece selector shaft as it's easier to check straightness & 're-engineer' to eliminate slop where the tie rod pushes/pulls it. I've commented previously about cursors & have taken to grinding back the faces of OEM Innocenti items decades old. I have never found any Indian/new 'Italian' cursors to be anything like fit for purpose.

The endplate & it's press in bush (to take the bearing) can give problems so substitution is the easiest check.

The wishbone is best fitted with a SHBS (Socket Head Button Screw) & Loctite.

There can be a tendency to fit cursor springs too strong, but perhaps your's is too weak?

Lastly, I always painstakingly get 0.003" axial clearance. I have shims that are all etched with their sizes, many of them created from old ones refaced on a surface grinder.

Good Luck with it!
Warkton Tornado No.1
 
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Re: 4th gear jumping out

Postby hullygully » Wed May 04, 2022 6:40 pm

also have a butchers @ the 'Cyclone 5' & AF's 5 x speed installation info bud ;)
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