Vespa Pre 1979 Large Frame Engine Work
Bearings - Crank Bearings
Main (Crank) Bearings
Older large frame Vespas use the same
bearings on either side of the crankshaft. Once the cases are split and
the crank and oil seal have been removed you can replace these
bearings. The bearings are part number 900100 and their size is
Above is a shot of the main crank
bearing left in the dutch side of the casing. It definitely needs to be
replaced, the casings need to be cleaned, and then a new bearing needs
to be installed. Typically the flywheel side bearing will remain on the
crank and the clutch side bearing will remain in the casing.
Once the oil seal has been removed, use a
socket or something similar to drive the bearing from the clutch side
by hitting it with a hammer.
The above is a shot shows the bearing
being driven through the casing and getting close to coming out.
Clean the casings once all the bearings are removed if yours
looks anything like what I started with. You can also install the oil
seal from this side (see oil seal
installation page) or just do it from the other side after the
bearing is in place. Heat the casings beforehand to make the aluminum
expand a little. There is no front or back side difference to the
bearing so it can go in either way.
A useful tip is to use the original bearing that was removed
as a drift to install the new one. Carefully tap down the new bearing
so that it seats squarely in the hole.
The other main bearing is typically left on the crank after
the casings are split. To remove this you either need to buy a special
tool, or just take it to your local scooter shop to have them pop it
off for you.
You can also use a basic bearing puller
to do the job if you don't want to spend the $60+ for the special
Piaggio type tool.
With the bearing off you can see the
area where the new bearing will sit (red arrow), and also the shoulder
(blue arrow) which stops the bearing from going all the way to the
crank web. This shoulder makes sure there is a gap between the bearing
and the crank for future bearing removal. To install the new bearing
you can freeze the crank and warm the bearing to make things easier.
When installing the new bearing make sure you support the flywheel side
crank web only. An easy way to do this is to slide a thick piece of
steel between the two webs and support it on either side. This is
imperative as you can bend the crank if the web is not fully supported
and you start banging away.
Use a large deep socket or a section of metal pipe to bang the bearing down on the shaft. The socket or metal pipe should only rest on the interior race of the bearing so it doesn't cause damage to the bearing.