Airleak /Oilleak LUI75

I have changed both oilseals (maghousing and driveside) on my LUI 75 in the winter as it burnt oil.
On the first rideout with the new oilseals I had a heat seizure after a short distance. Engine ran alright when cold but seemed to burn oil again when reved up (smoke from exhaust).
Is it possible that air is sucked from the gearbox. On series 3 engines I experienced that only oil is burnt when the driveside oilseal is blown. the crankcase is quite oily.

When I dismantled the mag housing I found out that the shim between the needlebearing and the crankshaft on the magside is missing. What`s the function of this shim ? Maybe air gets sucked from magside without the shim?
Does anyone knows a source for this shim or the correct dimensions.

Found the shim between mag bearing inner race on crankshaft.

So hopefully just the oilseal damaged when fitting the crankshaft. will see

Did rebuilt the front end this time with new viton sealring and used silicon sealant on gasket / sealring holding plate. Crankshaft looks perfect. Also checked the crankcase for cracks - nothing visible

But the f** lui is still burning oil when reved up.

Has someone had the same trouble or an idea to get problem fixed, as this is the third time I did rebuilt the frontend !!

No one got an idea what`s wrong !! Advice welcome.

I don`t have a glue what could be the problem Next step would be to buy new crankshaft / casa cylinder / new bearings / seealrings and plate and have a complete rebuilt of the topend. But there must be a reason for the oil beeing sucked plus seizure (no seizure marks on the barrel ? maybe bigend seizure ?

Thanks for help !!!

Good Evening
Could be the hallite washer not sitting flush and making the seal plate sit proud or seal plate screws bottoming ?

as shand says, i have found in the past that the halite washer is ever so slightly too big and can cause the seal plate not to sit flush, theres not much required to be removed from the washer/gasget but it needs to seat correct, were there any marks on the seal plate where possibly the crank has rubbed?
it seams that as its getting hot something is expanding and letting oil / air through, the engine should stall if its running and you block up the holes on the exhaust if not its drawing air.
hope that this helps a little.

when doing my multiple top-end rebuilds on my lui I found out that the halite gasket from the scootopia gasket kit is too thick. The gasket from the casa kit fits.

When fitting the scootopia halite gasket the alloy plate with the oil seal bend. Maybe the plate is warped now, but on my last rebuild I used an an glasplate to plan the oilseal plate.

Not startet with dissambling of the engine till yet. I collected a seal plate from an J125 which is made of steel rather than alloy and also got an double liped sealring.

Not sure if I buy a new crankshaft and do a full topend rebuild using a Casa 75 kit I already have.
Maybe I get the whole engine out this time to have a closer look if there are any hairline cracks in the casing ?

This might sound daft but could it be you have cured the oil leak and now your burning off the gathered oil deposits in the exhaust?

In the CASA Lambretta catalogue are different driveside oilseals for
LUI 75 and J125 (4gears) listed.

LUI75: 40 * 25,8 * 6
J125: 40 * 26 * 6

What driveside oilseals are you using ? Could a wrong sealring the reason for my troubles ?