Thread: LT95 rebuild for beginners

The layshaft is probably the most simple part of the box - a solid shaft with gears machined on it, and a bearing at each end.

Here it is bare with the bearings removed:



Other than gear tooth damage and bearing failure I can't see anything that might go wrong with it.

It does need the bearing pre-load set up if you are replacing the bearings, and since the gasket between the main case and the front plate forms part of the fit up, its probably a good idea to check the preload any time you fit a new gasket (even if reusing the same bearings).

The manual covers it in detail, but the basic procedure is to fit the shaft into the case (you have to have the mainshaft removed to do it), fit the gasket, bolt on the front bearing plate, and fit the adjusting shim and front cover plate. Once that's done you wrap some string around the layshaft, and check the rolling resistance of the shaft using a spring balance.
Should be 2.75-3.8kg.

Pretty straightforward stuff.

The tricky bit comes when you need to work out what size shim to put in to get the correct preload.
In my case I have new bearings, but have refitted using the original shim. When testing the preload using the method above the shaft starts moving at about 1kg, and settles at about 0.5kg to keep it moving, so I obviously need a thicker shim.

Is there a rule of thumb for shim thickness increase vs rolling resistance increase?

Steve

Originally Posted by 85 county

yes, did it work??

Pretty close. Here's what I did...

Problem for me (and will be the same for most other LT95 beginners) is that I don't have a box of shims to do the trial and error thing with.

What I DO have is the original shim as a starting point, and the gaskets that will be used for final fitment.
With those fitted I don't have enough preload (~0.5kg), so I need a thicker shim (or theoretically a thinner gasket).

Going by 85 County's approximation, I should need a shim about 0.19mm thicker than what I started with (extra 3kg x 0.625mm/kg )
The gasket between the front bearing plate and the front cover (foot in Blknight's terminology) is 0.41mm in my case, so if I removed that then by the same approximation I should end up with about 7kg preload.
When I did it the actual resistance was about 8kg.

Note: if you end up with too much preload when testing shim thicknesses you'll need to remove the bearing plate again and press the cup out slightly as it wont release the preload by itself even once you remove the foot completely.

I made a rough gasket out of heavy glossy paper that was 0.15mm thick, bolted it up and that gave me a preload of about 3.7kg (OK since the acceptable preload range is 2.75-3.8kg)

That means I need a shim that is 0.26mm thicker than the one I have (difference between the 0.41mm actual gasket and the 0.15mm glossy paper used for testing).

My conclusion from all of that, is that 85 County's approximation gives a reasonably good starting point, albeit on the thinner end (which is probably preferable anyway given my comment above on too much preload during setup).

Unfortunately the available shim range goes from 1.55-2.50mm, and I need 2.70 (which you cant make from that range).

Steve