Vespa smallframe engine strip down and rebuild.
2. Removing the cylinder.
you go any further here it's a really good idea to clean the engine
before you start unbolting things, to minimise the risk of debris
entering the crankcase or gearbox and damaging anything. The typical
well used Vespa engine will be in the filthiest state imaginable
with a greasy oily mixture of dirt, dust, oil, petrol, dead postmen,
bird's nests etc. get a stiff wire brush and attack it all to remove
all loose dirt. The cases then can be cleaned off with petrol, white
spirit, or some proprietary cleaner. Oven cleaner will shift anything
but most if not all brands will attack and discolour the aluminium
you are ready you can start dismantling the engine. Remove the cylinder
shroud. There is a hex head bolt at the rear, a Philips head screw
into the flywheel cover, a slot head bolt into the engine near it.
There is also a bolt on the clutch side which has often been lost
might as well remove the flywheel cover at this point too. Before
you remove the cylinder you should unbolt the exhaust manifold from
the rear of the cylinder. The inlet manifold goes into the cases
so you can remove the cylinder with it on, but you might as well
remove it now, and give it a good clean. The inlet manifold has,
under the rubber air bellows, a metal sleeve designed to give it
a bit of flexibility. It is held on with a circlip, which you should
prise apart enough to slip the whole sleeve off. Underneath you
will find a felt ring. This seals the join and should be cleaned
and soaked in a little bit of two-stroke oil before refitting.
cylinder on a 125cc engine is held on by long
bolts that go right through the cylinder and into the head. Undo
them and the cylinder
head will come off.
You can then carefully slide the cylinder up the studs to remove
it. On a 50,90 or 100cc engine the head is held on by separate
to the cylinder, and the cylinder studs are undone at the base
of the cylinder with a regular oen-ended spanner. Be careful
the piston receiving any damage when you remove the cylinder.
remove the piston you will need some internal circlip pliers to
remove the circlip that holds the wristpin in the piston. Actually
you can just about do it with nail scissors but they will be ruined
and you run the risk of damaging something (like your eyes) when
the circlip pings off. I still havent found out where my old one
landed! It's also a damn sight easier to use the proper tools and
they are cheap from shops like Machine Mart. You should really replace
these circlips with brand new ones. If you are kitting your engine
it will come with far superior wire rings to hold the wristpin in
place. Do not re-use the original circlips on a kitted engine.
only need to remove the circlip on one side, and you can use a flat
screwdriver to gently push the wristpin out of the piston by pushing
from the other side in the gap between the two ends of the remaining
circlip. You might need to tap on the screwdriver with something,
but either way the force needed should be very slight. The wristpin
runs in a caged needle bearing assembly which will either stay in
the crank small end, stay on the wristpin, or fall into the crankcase
- be ready to catch it to make sure it doesn't do the latter. The
bearings should remain in the assembly. If it doesn't look perfect
then replace it with a new one when you reassemble the engine.