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spacer cylinder base BGM original 172cc Piaggio 125-180cc 2-stroke 1.5mm (without cutouts for overflow channels) 49921
If a crankshaft with more stroke is used, this additional stroke must also be compensated for two reasons. On the one hand, due to the mechanical conditions to prevent the piston from hitting or the engine runs too highly compressed, on the other hand, to keep the control angles of the cylinder, which determine the performance, within reasonable limits.
. If the stroke is lengthened, the control angles are also lengthened. I.e. the scavenging channels in the cylinder (overflow and exhaust channel) are open longer. On the one hand, this is very good to generate more power, but on the other hand, this can also backfire if the control angles are no longer within a reasonable range or if the remaining existing components no longer support the achievable speed. The most significant change in the control angles occurs when the additional stroke is compensated for at the cylinder base. With a stroke increase from 52mm to 55mm, i.e. 3mm, 1.5mm would have to be underlaid at the base OR head. So no 3mm compensating seal is used but only 1.5mm because the piston moves 1.5mm up AND down.
. If now 1.5mm is underlaid at the foot increases, due to the angular function of the crank mechanism, the overcurrent time disproportionately to the outlet angle. Both angles, overcurrent and outlet angle, should always be in proportion to each other for a well-functioning flushing. The outlet channel should always open for a certain time before the overflow channels in order to give the old gases sufficient time to escape and make room for the incoming fresh gas. If the function of this process, called pre-discharge angle, is disturbed by an overflow angle that is too high (or an exhaust angle that is too short in relation to the overflow angle), the power delivery in the upper speed range will be massively disturbed. Then the best exhaust system simply no longer works because it lacks the surface to breathe. If the exhaust is then also a real racing exhaust that only makes music in the upper speed range, this is usually accompanied by a pronounced weakness in the lower speed range. Thus, the engine would then be slower than an original engine, despite multi-stroke and expensive exhaust, because the exhaust steals the torque out below and can not deliver the cylinder out above.
. Thus, a value between approx. 23°-32° must always be aimed for the advance exhaust angle. The smaller the angle, the less scavenging losses the cylinder has, but also correspondingly little power in the upper speed range. On the other hand, a large pre-discharge angle is perfect to support powerful exhaust systems, but carries the risk of losing a lot of power in the lower speed range.
. For starters, it is therefore usually more advisable to compensate for the overstroke at the cylinder head to avoid too high control angle change.
If a compensation at the cylinder base is sought, which is usually easier to realize with water-cooled engines, the exhaust angle must often be adjusted mechanically, i.e. the exhaust must be milled to achieve the desired advance angle.
This requires, however, depending on the cylinder type skill, tool as well as know-how.
A measurement of the control angle is just as inevitable as the subsequent adjustment of the ignition angle and the carburetor jetting.
Indispensable for all those who give their big Piaggio engine a long-stroke shaft and have to compensate for the longer stroke.
ATTENTION! the original foot seal must always be mounted additionally!
. If the stroke is lengthened, the control angles are also lengthened. I.e. the scavenging channels in the cylinder (overflow and exhaust channel) are open longer. On the one hand, this is very good to generate more power, but on the other hand, this can also backfire if the control angles are no longer within a reasonable range or if the remaining existing components no longer support the achievable speed. The most significant change in the control angles occurs when the additional stroke is compensated for at the cylinder base. With a stroke increase from 52mm to 55mm, i.e. 3mm, 1.5mm would have to be underlaid at the base OR head. So no 3mm compensating seal is used but only 1.5mm because the piston moves 1.5mm up AND down.
. If now 1.5mm is underlaid at the foot increases, due to the angular function of the crank mechanism, the overcurrent time disproportionately to the outlet angle. Both angles, overcurrent and outlet angle, should always be in proportion to each other for a well-functioning flushing. The outlet channel should always open for a certain time before the overflow channels in order to give the old gases sufficient time to escape and make room for the incoming fresh gas. If the function of this process, called pre-discharge angle, is disturbed by an overflow angle that is too high (or an exhaust angle that is too short in relation to the overflow angle), the power delivery in the upper speed range will be massively disturbed. Then the best exhaust system simply no longer works because it lacks the surface to breathe. If the exhaust is then also a real racing exhaust that only makes music in the upper speed range, this is usually accompanied by a pronounced weakness in the lower speed range. Thus, the engine would then be slower than an original engine, despite multi-stroke and expensive exhaust, because the exhaust steals the torque out below and can not deliver the cylinder out above.
. Thus, a value between approx. 23°-32° must always be aimed for the advance exhaust angle. The smaller the angle, the less scavenging losses the cylinder has, but also correspondingly little power in the upper speed range. On the other hand, a large pre-discharge angle is perfect to support powerful exhaust systems, but carries the risk of losing a lot of power in the lower speed range.
. For starters, it is therefore usually more advisable to compensate for the overstroke at the cylinder head to avoid too high control angle change.
If a compensation at the cylinder base is sought, which is usually easier to realize with water-cooled engines, the exhaust angle must often be adjusted mechanically, i.e. the exhaust must be milled to achieve the desired advance angle.
This requires, however, depending on the cylinder type skill, tool as well as know-how.
A measurement of the control angle is just as inevitable as the subsequent adjustment of the ignition angle and the carburetor jetting.
Indispensable for all those who give their big Piaggio engine a long-stroke shaft and have to compensate for the longer stroke.
ATTENTION! the original foot seal must always be mounted additionally!
Manufacturer Nr.: BGM ORIGINAL
EAN: 4251389144038
EU Responsible Person : BTS GmbH, Plochingerstrasse 41, Otsfildern, 73760, info@biketeile-service.de
Please note, that vehicle spare parts should only be installed by a qualified specialist workshop to ensure their proper function and the road safety of the vehicle.:
