Gearbox from BGM Pro for Vespa largeframe engines. Available with or without main shaft. The gears are made from high-alloy NiCrMo case-hardening steel (20NiCrMo2-2/ AISI8620) to withstand the highest loads. This extremely good base material can withstand even the highest motor power. The precisely defined surface hardening to 58-60HRC makes the pinions permanently resistant to wear. This makes BGM transmission parts an uncompromising material for any serious engine builder.
APPLICATION
The highly developed gearboxes can be used for all types of load, whether standard engine, tourer or racer. We offer the gearboxes in the PX125 (short fourth) or PX200 (original gear ratio). Both versions are compatible with the auxiliary shaft of the 125-200cc models. Sporty engines/riders use the option with a short fourth gear. The gear jump is then less pronounced and the engine is immediately reconnected to the power band.
FIT
The gearboxes of the Vespa Largeframe are roughly divided into old and new types:
PXold (-1983)
The old type was used until approx. 1983. It uses a main shaft in which the gears are only held on one side (Lima) by a circlip. It also has a cranked gearshift cross.
PX Lusso (1984-) also PX Disc, My, 2011, T5, Cosa
The new type has been used since around 1984, not only in the Vespa PX, but also in the T5, Cosa and their derivatives such as the LML Star 2-stroke and Stella 2-stroke. The so-called Lusso gearbox has two circlips on the main shaft and the gearshift cross is flat. This type is considered to be more stable than the old one, as the contact surface in the middle segment is wider and the main shaft is segmented, thus fixing the gearshift cross under load. The Lusso gearbox is recommended for engines from 25 hp.
Any PX engine with an old gearbox type can also be fitted with the gearbox parts of the later Lusso. In this case, it is only important to ensure that the main shaft, gears, gearshift cross, gearshift bolt and gearshift detent are replaced together.
SPECIAL CASES
PX80, VNA, VNB, VBA, VBB, Super, GL, Sprint, GT, GTR, TS, Rally
The PX80 engines and their predecessors (mostly still original with contact ignition) use their own gearwheels. However, these can easily be replaced with the ones offered here. In this case, it is also necessary to replace the countershaft/offshaft at the same time. Otherwise the gearing of the transmission parts will not match. The motor housing may have to be adapted to the larger seat diameter of the auxiliary shaft. It is often sufficient to remove the bushes in the motor housing on the auxiliary shaft mount (PX80) or to use a suitable auxiliary shaft.
To identify loose transmission gears, simply measure the center section:
The center segment on which the gearshift cross rests is
- PX old (up to 1984, cranked gearshift cross): 5 mm
- Lusso (from 1984, flat shift cross): 6.5 mm
The center segments of the BGM gear wheels are larger (approx. 1/10 mm) and thus offer even more contact surface for the gear cross. The gears have a marking (TOP) for installation direction. When installed, this should point towards the gear shift. The installation clearance between the gears and the shoulder ring should be determined using a feeler gauge and adjusted to approx. 0.15-0.35 mm.
TIP: The shift bolt has a left-hand thread. Therefore, loosen it by turning it clockwise.
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