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Polaris Repowered With Yamaha Motorcycle Engine
When Ed Pacha bought a used Polaris Magnum 425 ATV with a bad engine, he planned to repower it with a V-twin 750. However, when he tore into the Polaris, he realized he couldn't make the Polaris belt drive work with the 750's shaft drive.
"I found a 1981 Yamaha Virago 920 cc motorcycle engine that had a chain dri
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Polaris Repowered With Yamaha Motorcycle Engine ENGINES Engines 34-5-38 When Ed Pacha bought a used Polaris Magnum 425 ATV with a bad engine, he planned to repower it with a V-twin 750. However, when he tore into the Polaris, he realized he couldn't make the Polaris belt drive work with the 750's shaft drive.
"I found a 1981 Yamaha Virago 920 cc motorcycle engine that had a chain drive," says Pacha. "To use it, I figured I just had to substitute sprockets for the variable speed belt drive ahead of the Polaris gearbox."
Pacha kept both the high/low gearbox and the transmission and clutch from the 920. That gave him 10 speeds forward and retained a reverse gear. Drive chains to the front and rear axles from the back of the gearbox didn't have to be changed. In fact, the only major change was to split the Polaris frame ahead of the gearbox and add 7 1/2 in.
"Spreading the frame made room for the engine and, once I made mounts, I just dropped it in," says Pacha.
Other minor changes included eliminating the foot brake from the Polaris, replacing it with a master brake cylinder from the motorcycle, and adapting the brake lines. He also mounted the Virago brake lever on the right handle bar. Pacha mounted the Virago clutch lever on the left handlebar. The high/low control also had to be remounted.
Pacha says his repower is a work in progress. He has a temporary fuel tank mounted to the front rack and has yet to make a cowling to cover the engine. His biggest challenge will be reworking the gearbox. While everything works great and he has tremendous torque, top speed is only 12 mph.
"The variable speed belt drive is what gave the Polaris its higher road speeds," says Pacha. "I may try to put a planetary gear on the drive end of the gearbox or simply rebuild the gearbox altogether. I've reworked the sprocket ratios all I can."
Pacha asks FARM SHOW readers with ideas to give him a call.
Contact: FARM SHOW Followup, Ed Pacha, 3263 Highway 78, Brighton, Iowa 52540 (ph 319 694-4108; govenorbrn@yahoo.com).
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