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1986 onwards Honda CR250 CylinderThe CR250 went water cooled in 1981 and early models have a steel bore surface and no exhaust valve system. The 1984 & 85 models have the ATAC exhaust system, and 1986 models onwards have different versions of an HHP exhaust powervalve system and a Nikasil plated bore. The HPP System: The Honda Power Port system works by using a complex system of linkages to change the height of the exhaust port openings within the barrel. At low RPM the two sliding valves on the top edge of the exhaust port are closed. At higher RPM they begin to open which effectively raises the height of the port, until they are fully open at high RPM. This changes the exhaust valve timing depending on the RPM range which allows the best exhaust timing at any RPM. The physical characteristics of the barrel are different from the other Japanese manufacturers. The exhaust valve enclosure is big. It is easily the widest part of the barrel. If this was to be added to a scooter with a non standard 60mm crank you would need to remove some metal to change the height of the barrel and it appears that this could be done without affecting the exhaust valve system. |
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Intake View
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Exhaust View
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Intake View
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Right Hand Side View
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Exhaust Valve View
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Right Hand Side View
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