Vespa Pre 1979 Large Frame Engine Work
The transmission on a Vespa comprises of two main parts (other than the clutch). 1) The input shaft sometimes referred to as the christmas tree (because it looks like one) and 2) the output shaft. The input shaft is a sold piece where all the gears rotate as one on a shaft. It has individual needle rollers on the flywheel side, and a central bearing inside the gear housing on the clutch side.
The output shaft has the gear selector cruciform in the center and turns on a ball bearing on the wheel side and a caged needle roller bearing on the flywheel side.
The following images assume you have
already dropped the engine
removed the rear wheel, and split
the cases. The pictures below show the clutch out of the bike too,
but it isn't necessary to remove the transmission.
The first step is to remove the entire
output shaft with all the free gears still on it. Take a rubber faced
mallet and use either a block of wood or reverse the axle nut on the
axle to protect the threads, and start hammering. The axle is a tight
fit in the axle bearing but it should start to move out.
Support the output shaft and the free
gears as they come out of the casing. Put these to one side to
concentrate on the input shaft which is still in the casing.
Have a look at the side of the clutch
cover and you'll see a small nut coming through the casing. Clean it if
it is really dirty, and then use a screwdriver to bend down the tabs of
the washer that stop the nut from rotating.
Using a ratchet or a wrench, remove the
single nut on the end of the shaft.
...followed by the washer....
...and then the tab washer. The tab
washer will also have another tab that slots into a keyed groove in the
end of the output shaft..
The input shaft doesn't turn. The
christmas tree turns on the shaft and has bearing at either end. Before
very lightly tapping the shaft on the end, make sure you have another
hand over the end of the output shaft (see the next picture).
Carefully tap the shaft into the casing,
but not all the way through. As the end comes clear of the christmas
tree, the needle rollers will fall out of the end. Keep these in a safe
place as they can be reused. Once you have all the rollers out, pull
the shaft until the christmas tree drops out of the casing.
The christmas tree can now be removed