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  1. #1

    driveshaft length and strength and welding?

    building a yamaha powered bass boat. Putting the engine ahead of the driver. How long can a driveshaft be and what might the strength be? I am using a fx140 motor, midwall bearing support. was considering taking 2 stock driveshafts, machining a morse taper onto the shafts pressing them together then tig welding them. then final turning down the weld. so from the pto of the engine will go to a pto coupler with the mid bearing support. driveshaft will have factory splines into the mid bearing. driveshaft will extend back to the pump and have another pto on the end. mating with a second mid wall bearing support and coupler.
    anyone see any problems with this?

  2. #2
    Hydrotoys's Avatar
    Join Date
    Jul 2005
    Mesa, AZ
    Without support, such as mid-shaft bearings, I see them whipping so hard they break in half, or launching through the bottom of the boat.

    Consider doing your shaft-into-shaft design but do NOT weld. Instead use some type of dedicated driveshaft supports at the midpoint, on one of the shafts. This could cut down on cost, and make it possible to replace without ripping the whole thing apart.

    Alignment will be crucial. Any misalignment will eat your system over a relatively short period. Consider some type of alignment jig before final assembly.

    Avoid those flimsy crappy rubber finger setups you see on the Yamaha/Kawi's. They will break, and are prone to push laterally on the shafts as well, as the rubber deflects.

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