Vespa Pre 1979 Large Frame Engine Work
Oil Seals: Flywheel Side
There are three main oil seals in a older Vespa engine:
There are also some more minor seals around the kickstart quadrant, the clutch cover, and the rear wheel back plate.
The main seals should be replaced every time the engine is taken apart as they are cheap to buy but they are buried pretty deep in the engine. If you have the engine apart you might as well drop them in.
Flywheel side seal: The flywheel oil
seal on an older model large frame bike
is different to the P series equivalent. The main difference is that
the engine uses the same large bearings on both sides of the crank and
both main bearings are lubricated by the gasoline/oil mix. On P series
bikes the clutch side main bearing is actually lubricated by the
transmission oil because the oil seal is located between the crank and
Once the casings are split you can flip
over the flywheel side casing and use a large socket to remove the seal
by tapping it through the casing. It doesn't matter if it gets damaged
as it is going in the trash.
In high mileage motors they can look
pretty nasty. Clean the area all around where the main bearing and seal
go. Be sure to have a look where the arrow is shown above to make sure
that the bearing lubrication hole is clean. Blow through it with air if
necessary. If this hole is blocked your bearings may not get proper
With everything clean, fit the new oil
seal as shown. Make sure the cut out in the metal portion aligns with
the oil lubrication hole in the crankcase. It is important that these
align and the oil hole is clean. The oil seal itself should be
installed so that the small circular spring is facing the crank (as
If you are replacing your main bearings,
a little trick I learned to install the seal and seat it squarely is to
take the one of the original bearings and carefully grind the sides
down so it fits in the main bearing hole without any resistance. You
can then keep it in your tool box for future rebuilds. With the
diameter reduced just slightly it is the perfect tool to use as a drift
to seat both the flywheel and clutch side bearings.
Above is a shot from the stator side of
the flywheel casing with the seal pushed fully home.