Revision - dismantling the engine of the Vespa V50 / PK 50 S-XL2

This guide explains how to disassemble a Vespa Smallframe engine step by step as part of a revision.
Although the video shows disassembling a Vespa PK 50 XL2 engine, the instructions also apply to Smallframe engines of the PK 50-125 S/XL and the Vespa 50. The Smallframe engines are virtually identical except for some details. A revision becomes necessary at the latest when problems with false air that cannot be fixed from the outside occur, or when a change of ball bearings is necessary, if something is blocking inside the engine, or if it is leaking and losing gearbox oil.

All steps at a glance

To loosen the four nuts at the cylinder base, the flywheel is first removed because the Elestart ring gear obstructs access to the front two nuts. Removal of the flywheel is accomplished using a flywheel puller. With the flywheel removed, the ignition, which is secured to the engine housing with three slotted screws, can be removed from the engine housing.

Removing Vespa flywheel Vespa ignition

Now all four nuts at the cylinder base can be unscrewed. Then pull off the cylinder upwards and remove the piston from the crankshaft. The piston pin is secured on each side by a circlip. Remove these two circlips using suitable circlip pliers.

Vespa engine revision and disassembly of the cylinder Piston removed with circlip pliers

The brake drum is removed to access the brake backing plate underneath. Then loosen the three screws of the brake backing plate and remove the entire brake backing plate from the engine housing.

Vespa PK 50 brake drum Vespa brake backing plate

Then remove the clutch cover, remove the pressure plate, and remove the clutch using a clutch puller.

Vespa PK 50 XL2 clutch cover Pressure plate for XL2 clutch XL2 clutch with inserted clutch puller special tool for engine revision Nut loosened for disassembling XL2 clutch

After removing the clutch, the primary pinion is dismantled, which is bolted to the crankshaft.

Locking plate from primary pinion to be renewed during engine revision Primary pinion on the Vespa crankshaft

After the centering bolt and nuts of all engine bolts have been loosened, the engine halves can be split and disassembly continued inside. The splitting process can be facilitated by operating the kickstarter. The housing should never be levered.

Vespa engine housing with engine bolts Vespa engine halves in slightly split condition Vespa PK 50 engine halves in disassembled condition

How much does an engine revision cost?

The complete overhaul of a Vespa engine depends on the hourly rate of the workshop and the work to be carried out. For disassembling the engine, replacing the oil seals, ball bearings, and rubber parts, and assembling the engine, you should plan for about five hours. This would result in around €300 plus VAT at an hourly rate of €59 net (that's what my plumber charges) for 5 hours, with the cost of spare parts to be added. The time and cost increase if the shift fork needs to be overhauled and if repairs need to be made due to rounded nuts, seized engine bolts, damage to the engine housing, etc. Not to mention tuning measures.

DIY

The configurable engine revision kit allows the guided compilation of the parts necessary for an engine revision.

To the engine revision kit.

Further Notes

If the engine has already been disassembled once, all wear parts should be replaced
Before disassembly, the gear oil should be drained.
Cleaning the engine before disassembly can help reach some screws and nuts hidden under dirt.
All required Vespa spare parts are available in the shop.