Rebuilding a vintage Vespa engine is not hard to do, but you will need specialised tools to get the job done right.
Remove the muffler, drain the engine transmission oil, and disconnect all electrical wiring, petrol lines and control cables.
Remove the rear wheel and disconnect the rear shock absorber and swingarm bolt. Relocate the engine to a well-lit work area. Loosen and remove the rear wheel hub and nut.
Use the flywheel fan locking tool to secure the flywheel and remove the securing nut. Use the Vespa flywheel fan removal tool to remove the fan. Next, remove the clutch engine case cover. Secure the clutch with the clutch locking tool and loosen the assembly with the clutch nut tool. Pull the clutch out.
Remove the cylinder by loosening the cylinder cap. Next, remove the flywheel stator and carefully remove the wiring. Loosen the gear box cover below the flywheel area and remove it.
Unscrew and remove all engine case bolts. Gently tap the flywheel side of the case with a rubber mallet to loosen it. Tap more if it is stuck.
Remove the flywheel engine side. Tap the crankshaft assembly out of the clutch side bearing with a metal punch and hammer. Remove the crankshaft when loose, remove the transmission cluster and tap out the rear wheel axle and gears.
Clean the engine case, remove the old oil seals, remove the bearing circlips if present, remove any bearing securing tabs (clutch side) and tap out the old bearings (they should not be reused once the case is opened).
Use freezer-cold bearings and a propane burner for bearing installation. Make sure only to heat the case. When hot, take the cold bearing and install it quickly using a bearing punch or a socket the size of the outer rim of the bearing. Grease it, and install the securing circlip. Install the new oil seals and securing tabs again.
Tap the crankshaft with a punch and hammer from the flywheel side so that it seats into the clutch bearing centre.
Reinstall the transmission cluster. Secure it with the transmission spacer, tab washer and nut.
Disassemble the clutch using the clutch compressor tool. Replace the cork pads, and grease the clutch plates and cork plates with fresh gear oil. Reassemble the clutch. Put the new clutch woodruff key on the crankshaft and reinstall the clutch assembly. Place the clutch tab washer on next and finish with the securing nut. Use the clutch locking tool and clutch nut tool to tighten down the clutch with a torque key.
Take the rear wheel axle and gear set and tap them through the new rear wheel bearing. Make sure the gears mesh and line up with the transmission cluster.
Install a new engine case gasket. Make sure the kickstart spring is embedded with a thick glob of grease and reinstall the flywheel case side. Make sure the engine sides match up, activating the kickstart lever slowly to fit the gears. Install all engine case bolts and nuts.
Place a new cylinder gasket on the engine and reinstall the cylinder. Secure the cylinder cap and tighten it down with a torque key using a diagonal cross pattern.
Reinstall the stator plate on the flywheel side, install a fan woodruff key on the crankshaft and tighten down the flywheel fan. Reinstall the clutch cover. Use a new gearbox gasket and reinstall the gearbox. Reinstall all covers necessary and the carburettor assembly.
Reinsert the engine back into the scooter, reconnecting the swing arm bolt and rear suspension. Reconnect the electrical to the engine and the fuel/oil lines back to the carburettor. Reinstall the muffler with the securing bolt. Reconnect the clutch, gear shift and rear brake cables for control.
Use a torque key for tightening. Failure to do so can result in parts coming loose or over-tightening, which can damage the engine case itself.
Never reuse old bearings, gaskets or oil seals. Reusing bad parts can result in engine failure when riding.