1976 Vespa Sprint Veloce

Full Mechanical Restoration Project

  • Gearbox Restoration

    Original State: Fully jammed gears, layered sediment, worn cruciform

    Restored State: Full gear mobility, zero rubbing or sticking gears, improved gear selection via gear cam

    • Correct shimming of gear cluster to spec (0.4 mm)

    • Removed and upgraded cruciform

    • Full clean, re-oiling, and reassembly of gear stack and shaft

    • Ball bearings replaced, pin-cluster bearing reassembled

    • Gear cam refurbished with new gaskets

     

    Challenge: original vespa shims left a clearance of 0.1 mm, this was causing restricted motion of the top gears. However, removing one of the two shims left a clearance of 0.7 mm, causing gear vibration.

    Resolution: a single, much wider shim was sourced to ensure the clearance was 0.4 mm (+/- 0.1 mm). This was measured using vernier callipers.   

  • Carburettor Rebuild and Tuning (Dell’Orto 20/20)

    Original State: Very dirty, old jets, degraded filters

    Restored State: Fresh filters, full rebuild, new jetting, new gaskets, racing air filter and venturi induction kit installed

    • Full teardown, clean, and rebuild

    • Fresh gaskets and filters fitted correctly

    • Pollini Racing air filter and venturi kit installed

    Jetting:

    • Main Jet: 125

      • Unmodified suggestion: 98

      • Installed Pinasco 177cc cylinder: 108-114

      • Installed Pollini venturi kit: +10-15 -> 125

    • Air Corrector: 160

    • Idle: 48/160

    • Atomiser: BE3

    Next steps: Running a rich fuel mix on a 125 main jet. This is then expected to be lowered to a 120 or 122 after the engine has been run for a few hours.

  • Clutch Replacement

    Original state: broken 20-tooth clutch, not seating correctly

    Restored state: new 22-tooth clutch seated correctly, rotates with zero interference

    Clutch upgrade decision: considering the increase from 150cc to 177cc, and upgraded air intake, I made the decision to move to a 22-tooth clutch. I considered that the additional power supplied by the new parts (expected + 6-9 hp) would retain lower-range acceleration and overcome the increased resistance, while the higher tooth count would create smoother power delivery overall and a more stable top-end.

    Challenge: clutch would not seat all the way onto the crankshaft

    Resolution: I used a circular dremmel bit to gradually remove material off the inside of the clutch. This was done one pass at a time with constant seating checks on the crankshaft. Once it was comfortably sliding on 75% of the way I torqued the retaining nut lightly to pull the clutch the remaining few mm onto its housing. The final torque setting was 35 Nm.

  • Piston Cylinder Upgrade (Pinasco 177cc)

    Original state: missing cylinder, considerable piston damage, heavy carbon deposits, jammed crankshaft bearings

    Restored state: unhindered crankshaft rotation, brand new piston, cylinder, gaskets, and bearings

    • Piston head squish adjusted to spec (1.5 mm)

    • Crankshaft polished and rebuilt

    • Upgraded crankshaft and gudgeon bearings

    • Fuel inlet slightly increased for higher power

    • Crankshaft correctly floated on case assembly

    Challenge: both crankshaft bearings were jammed in the crankcase along with their oil seals due to age-related deposits.

    Resolution: careful removal of old seals with sharp pliers, heating the crankcase to free the stuck bearings, and using WD-40 to break down sediment. New bearings were placed onto the crankshaft before being inserted into the crankcase to avoid incorrect seating.

Gallery