Gearbox Shimming trouble

[inch71]

I'm doing a full engine rebuild over the winter, with new bearings & seals etc. I'm having real difficulty in shimming the gearbox. I'm using a Casa rear hub bearing with an LI 150 gearbox. I can get the shim (2.4) to fall within the tolerances, (0.15 fits, 0.20 is too tight) but as soon as I torque down the endplate, everything becomes really tight. I can turn it using the hub, but it's far too stiff. If I slacken the bolts off, then it obviously turns easier. I dropped down a shim size to see if this made any difference. The gap was too large on the tolerance, but again when torqued up it was stiff to turn.
Any ideas, as I'm stuck what to do next.

[berniek]

Of course it may be that you need a thinner shim, but first put on your crown wheel and spider and tighten up the clutch nut, will pull the cluster into place, check again then. Good luck

[Captain Pugwash]

Have you tried fitting the clutch sprocket and 22mm nut to pull the mainshaft up through the endplate bearing then try to spin the gears ?

[Wack]

You need to make sure the layshaft is fully pulled thru the hub bearing by fitting the hub or a spacer then tightening the nut. Then fit the gears and check they are higher than the layshaft, if not they will lock up when the endplate is tightened. As said before either fit the spider and nut to pull thru the bearing or hit the cluster with a nylon hammer as this often settles things and lets the box turn freely. Also check the endplate bush is fully seated. Some hub bearings are slightly wider which then places the layshaft nearer the endplate.

[inch71]

I've fitted the hub & torqued it up to 120ft/lbs, so the layshaft is pulled fully through. I'll try the clutch spider another day & see if that helps.
How far below the gears should the layshaft be? As with the naked eye, it looks like they're are sitting about level

[Wack]

I don't know of the ideal step but as long as the gears are taller the you should be ok as if they are level then the shim will lock the layshaft and gears together. If this is the problem and you have no other replacement parts to try then you may need to have the layshaft skimmed a little so the gears are higher, also look at the thrust faces on each gear and the layshaft stop for wear.

[al pushpak]

Hi if you have a copy of Stickys lambretta manual to hand then you may want to check out page 58 there's a section right at the top that refers to this type of problem, hope you get it sorted. cheers. al

[pip]

A scooter mechanic I know was having problems with a Casa bearing and found the gearbox was to tight when all fastened up and on checking found the bearing to have been manufactured to the wrong size.

[inch71]

Since getting the Casa bearing, I've heard a couple of things about them, where people refuse to use them again, as they had nothing but problems with them. I thought I'd go for that as Casa is usually a name you can trust, & I thought it would be better than an Indian one

[trotsky]

Hi all, please remember as good as an Li150 box is, the problem with them was/is them is the wear (also rear hub bearing height). Please check that 1st gear cog clears the layshaft, otherwise shimming the gearbox is impossible. The 1st gear cog needs to clear the layshaft end, otherwise when you torque down the endplate the shim will tighten on the layshaft instead of 1st gear & lock the gearbox. Unfortunately it is a common fault on LI150 boxes. Wack's explanation is spot on...
Hope this helps Steve

[inch71]

It was running fine before. I stripped it to replace all the bearings & seals before I put s new Mugello top end kit on. I didn't check what the clearances were before I stripped it. In hindsight I wish I had, so I'd have had an idea what it was running at. It's onlt since replacing the bearing for a Casa one that I've had the trouble. Hence the question

[Wack]

If it is actually the hub bearing that is a fraction too wide I wonder if it possible to fit a spacer under its step into the casing by the required amount to save having to buy a new bearing? I couldn't see a problem here as the bearing doesn't sit flush anyway.