Adapter plate set BGM PRO 210cc Ø68.5mm 2% J&G crankshaft for Vespa PX80, PX125, PX150, Co

Adapter plate set for big bore cylinders incl. BGM crankshaft suitable for any engine with three overcurrent channels and the PX crankshaft type (recognizable by a pole nut with M12 thread). This kit is required for mounting a Polini / Malossi 210cc cylinder (Ø68.5mm) on Vespa PX80, PX125, PX150, Cosa125, Cosa150, Sprint Veloce150 (VLB1T 294260-) engine cases.
The adapter set includes:

• 1x crankshaft BGM031125G 60mm stroke, connecting rod=125mm
• 1x adapter plate steel 14mm
• 1x aluminum spacer 1.5mm
• 4x stud bolts M8x165mm
• 4x screws M7x25mm

In order to convert this engine to 221cc, you will need the adapter set as well:

• Malossi 210cc cylinder incl. cylinder head (M3118591)
• PX200 exhaust
• Longer gear reduction
• Reinforced clutch

ADAPTER SET
The conversion is based on a crankshaft with a 20mm longer connecting rod (125mm instead of 105mm). The solid CNC-milled steel adapter plate is screwed onto the engine housing and accommodates the stud bolts for the PX200 cylinder. A 1.5mm thick aluminum gasket between the adapter plate and cylinder base seals the bolt holes and ensures the correct installation height.
MALOSSI SPORT
The SC80210 adapter set is designed for use with a Malossi Sport 210 cylinder. However, it is essential that the engine housing is spindled out as the Malossi cylinder base cannot be shortened without losing stability. In conjunction with an adapted engine housing (intake, transfer ports), the use of an SI24 carburetor and a good box (Polini, BBT V2 etc.), the engine delivers over 20 hp/22 Nm with a very nice speed range and high torque at an early stage.
CRANKSHAFT/INLET
The BGM crankshaft fits into the engine housing of the PX80-150cc models without modifications. It has adapted timing angles and harmonizes perfectly with the intake of the PX80-150cc models. Due to the lower pre-compression, the converted engines work more harmoniously with shorter intake angles. This means that the intake control angles of 120° f.o.t. to 70° n.o.t., which are otherwise obligatory for sports engines, are not absolutely necessary for good performance. Tests on our engines have already produced very good results with 115°/60°.
CARBURETOR
The standard carburetor (SI20/20D) can be retained as long as it is adapted by the jetting (use the basic tuning of the PX200). However, the carburetor of the PX200 models (SI24/24E) provides more power and torque. This also has the appropriate jetting. To fit the SI24 carburetor, the carburetor bowl should be adapted in the passage (this can be done quickly with a file or a Dremel/Proxxon tool).
TRANSMISSION
To make good use of the significantly higher and early torque, the reduction ratio should be extended:
80cc
The PX80 has its own secondary gearbox which is very short (originally the third gear of the PX200 already has a longer reduction ratio than the fourth gear of the PX80). If the PX80 gearbox is to be retained, it can be used with an extra long reduction primary from e.g. BGM (25/62). This is used in conjunction with a stable clutch of type COSA2, e.g. a BGM Superstrong clutch. Alternatively, a gearbox from the PX125/150 models can also be used in the PX80 engine housings with minor conversion work. To do this, either the diameter of the auxiliary shaft axle on the alternator side is turned down or the engine housing is enlarged at the mount for the auxiliary shaft (remove the existing bushing).
125/150cc
For the 125/150cc engines, it is sufficient to change to the components of the 200cc engines on the primary side (primary wheel 64 (BGM) or 65, clutch pinion 23 or 24 (BGM) teeth).
CLUTCH
The 80-150cc models up to model year 1998 still use small clutches with 6 springs (108mm basket diameter). These are permanently unable to cope with the high torque of 200cc engines. They should therefore be replaced with a corresponding clutch for 200cc models. A good option is to change directly to the most modern clutch type of the COSA2 models. The BGM Pro Superstrong is a very high-quality and stable clutch that is also easy to operate.
IGNITION/POLYWHEEL
These can easily be taken over from the donor engine. The ignition setting is made according to the cylinder (18°-23° from top speed). Of course, other ignitions/pole wheels can also be used for further tuning purposes. Our test engine ran with the pole wheel BGM Touring with 2300 grams, which harmonizes very well with the performance characteristics of the 200cc engines.
CYLINDER HOOD
Due to the 15mm increase in cylinder height, the cooling hood must also be extended accordingly. We simply used two hoods and cut off the lower third of one of them. We then connected this to the complete other hood using conventional self-tapping screws. Of course, this can also be done more easily, but for us this method has also proven itself in everyday use. Alternatively, the hoods can also be welded with a soldering iron. Special plastic welding rods are also available for this, but as a rule you can also use the remains of the sacrificed hood as filler material.
EXHAUST
Due to the higher cylinder, the exhaust may have to be adapted. Our experience has shown that the Polini box systems have to be modified (twist the mounting brackets). The BGM Touring V2 systems (BGM1011TR2), on the other hand, worked on our setup without any adjustments.
CYLINDER DISASSEMBLY
Due to the raised cylinder, it is not possible to remove the cylinder head/cylinder as long as the engine is installed in the chassis. Alternatively, the stud bolts can be locked with our BGM72M7 tool and unscrewed from the adapter plate when the cylinder is fitted. In this way, both the head and the cylinder can be removed with the engine suspended in the frame. This is not normally a recommended procedure as the threads in the soft aluminum of the engine housing are not designed for frequent disassembly/assembly. The original stud bolts from Piaggio have a thickening on the thread on the side where they are screwed into the engine housing, which causes them to jam in the housing. However, due to the other stud bolts we use and the steel adapter plate material, this is completely uncritical.