the bgm Smallframe gear wheels

The bgm Smallframe gears, main and auxiliary shafts are manufactured in Europe to the highest quality standards. In addition to the high-quality material used, the tempering of the components also plays a major role. For this reason, all transmission parts such as gears, auxiliary shafts, main shafts and the shift claw are individually tempered at thyssenkrupp. The high-quality material, the dimensional accuracy due to the precise production and the "know how" in the tempering process result in an extremely resilient transmission part.

Load test

To ensure that the gears can withstand a high load over the long term, the components were subjected to a load test in a German test laboratory for gear drives.

In this so-called pulsator test, the gears are clamped across several pairs of teeth and hydraulically loaded with a pulsating force on the tooth flanks.
This test is deliberately carried out until the material fails so that the durability can be determined and compared.

To explain this roughly using an example:

The bgm gear III was subjected to a pulsating load of 8kN with 64,000 load cycles until the provoked failure. With a lower test load, i.e. less than 8kN, no failure could be generated during the test. By way of comparison, a third gear from a Piaggio gearbox failed after 33,000 load changes in this test. This means that the fatigue strength of the third gear in the bgm is approx. 90% higher than the original Piaggio component.

If you translate this laboratory test into road performance, this test load corresponds to an engine with over 50 Nm of torque at the crankshaft, which is driven at full throttle for just over 1000 km at a time.

The bgm Smallframe gears are available in the familiar gradation of 58, 54, 50, 46 and 48 teeth. The tooth profiles of the bgm gears are based on the Piaggio gears of the gearbox type with the "42" marking and therefore the bgm gears also have the same range of use as the Piaggio original gearbox. The fourth gear with 48 teeth is an exception here. This gear may only be combined with auxiliary shafts with 22 teeth on the fourth gear.

The bgm Pro auxiliary shafts are all supplied with a high-strength nut for fastening the clutch. To ensure the highest possible strength of this screw connection, the auxiliary shafts are manufactured with a fine thread M10x1.

We offer matching auxiliary shafts with three different gradations for the gear wheels:

bgm01822: 10-14-18-22

the original gradation,

On this auxiliary shaft, all bgmas well as gear wheels that correspond to gearbox type 42. So also gear wheels e.g. from Benelli, Fabbri, OEM which are suitable for the original Piaggio gearbox.

bgm01821; 10-14-18-21

The "short fourth gear"

Here the jump between third and fourth gear is one tooth shorter in fourth gear. The difference in speed when shifting from third to fourth gear is reduced by approx. 400 rpm and helps to achieve a better gear connection. If the same top speed is to be achieved in fourth gear at the same engine speed, a primary 27/69 (2:56) with a primary gear z28 can be used. The top speed remains the same, but with the advantage of a better connection when shifting from gear three to gear four. This secondary shaft can only be used with the fourth gear with 46 teeth on the main shaft. Due to the reduction of one tooth on the fourth gear, this auxiliary shaft is the most sensible way to shorten the gear jump. Due to the distribution of only 21 teeth on the same diameter of the auxiliary shaft, the tooth bases are significantly wider and therefore more stable. The combination with this auxiliary shaft in fourth gear (46:21 = 2.19) corresponds approximately to the use of the short fourth gear with 48 teeth on the main shaft with an original auxiliary shaft
(48:22 = 2.18), but is significantly more durable.

bgm01720: 10-14-18-20

The gradation short third gear, short fourth gear

The jump from gear two to gear three and from gear three to gear four is significantly reduced. Also only suitable for gear wheels of gearbox type 42. Compared to the original gradation, third gear is one tooth shorter and fourth gear is two teeth shorter. As with the auxiliary shaft with the short fourth gear, this makes the teeth on the third and fourth gears more stable thanks to wider tooth bases. "THE" countershaft for fast and high-torque engines that are equipped with a long primary reduction ratio or are clearly speed-oriented with a short primary reduction ratio.

The bgm Pro auxiliary shafts

The bgm Pro auxiliary shafts are just like the bgm Pro gear wheels are manufactured and tested to the highest standards. For example, in direct comparison with a Piaggio auxiliary shaft, the third gear of the bgm Pro auxiliary shaft was tested for durability at 150,000 load cycles and the Piaggio auxiliary shaft at 58,000 load cycles in the pulsator test.

In comparison, the third gear of the bgm auxiliary shaft is over 150% longer than the durability of an original Piaggio auxiliary shaft. A clear plus in safety for engines with a power increase.

Here is the usability of the various auxiliary shafts on the respective gear wheels

In future, the gearboxes will also be fully assembled with shoulder rings, reinforced shift springs, our new bgm Pro Sport shift claw. The play of the gears is minimized by the matching bgm Pro shoulder rings and the main shaft can be fitted directly.

Gearbox (gears incl. main shaft)

With the bgm Pro gearbox for the Vespa Smallframe, we provide you with an extremely resilient solution for your gearbox. Thanks to the available variants, the bgm Pro transmission can be individually adapted to almost all engine concepts and personal preferences in terms of riding characteristics.

bgm shift claw

bgm PRO SPORT- 4 speed, H=50mm,

VESPA PK50, PK80, PK125, V50 (V5A1T from 69444), Special (V5B3T from 94315), Elestart (V5B4T from 1514), PV125 (VMA2T from 150203), ET3 (VMB1T from 8161)

BGM PRO has given the successful BGM6550 shifting claw an update. The successor BGM6555 has a completely redesigned detent profile. This makes the gears even more precise and completely eliminates the dreaded gear jumping.

The BGM Pro shift claw is made from high-quality 15CrMo5 (SCM415) chrome molybdenum steel and is therefore extremely durable. The flanks have a very narrow tolerance compared to other gearshift claws available on the market. This ensures that the claw is guided precisely in the main shaft and effectively prevents shifting/tilting.