Figuring out what motor to retrofit? Hmm..

Discussion in 'General Questions' started by MrCrowley, Oct 12, 2007.

  1. MrCrowley

    MrCrowley Guest

    Ok, for my lawnmower engine idea, I pulled the trusty, rusty lawnmower out of the shed yesterday to look at it from the viewpoint of propulsion and not mowing grass. The biggest problem I have is that all my motors 26hp, 16hp, and 6.5 hp are all bottom shafted. However, thats great if I decide to use a riding mower transaxle. With taller bicycle wheels, is should gear up to bicycle speeds. Pulleys would gear it higher if need be. This would then be mounted in the trailer/ or side car "frame". This way, the fan belt from pulley to pulley can always act as a "clutch" using the transaxle route. This is great if using riding mower systems.

    However, this little 6.5 intrigues me because it has a side shaft PTO gear for self propulsion- and gear reduced already. I think it is a small gearbox bolted to the bottom of the 6.5. I turned the blade by hand, and it is either 8:1, or 9:1 reduction (was getting dark). It is from a circa 2000 Scotts pushmower. Is this an ideal reduction speed? Im thinking it would be enough, and any more gearing changes could be accomplished via the jackshaft/ fan belt pulleys.The cool part is, I could use a fan belt with a cabled tensioner as a clutch like a riding mower, and go straight bicycle the rest of the way. fan belt jackshafted to MTB triple rings, via chain to a MTB rear wheel with maybe dura ace cassette? Hmm. A 30 speed! This should negate any slightly of gearing problems. More than enough to pull a load straight up a hill, and more than enough to still apply engine power on the downhill white knuckle rides:eek: Also, if I could use a MTB suspension fork to mount the wheel, having a true bicycle setup on this separate frame, the rear derailleur could tension the chain as the suspension flexed. Wohoo!

    If I decide not to do any of these, I may have to go and buy a true side shaft motor. I do still have a weedeater engine I could yank, but I dont think its enough power for a trailer/sidecar plus stuff. To me this really seems do-able, or am I just crazy? I think I should really spend a couple of weeks with the gearing calculator for every gear before fabrication begins.
    Last edited by a moderator: Oct 12, 2007

  2. Alaskavan

    Alaskavan Guest

    Staton uses 18.75:1 reduction and an 11-14 tooth drive gear going to a 16 tooth final (I think). That's with engines providing 1.5 to 2.5 hp. Your torque and hp ranges will probably be very different from the small engines, but that might give you some idea where you're starting from.
  3. MrCrowley

    MrCrowley Guest

    I guess if all else fails, after its assembled, the jackshaft pulley/ring could be continually modified in diameter to fine tune everything. If I end up to tall or too short, I could just remove the too high/too low gear from the MTB front and go to say 20 or 10 gears. Still doesnt sound bad at all to me! Ill probably have to carry spare chain links if I yank too hard on the throttle. Lol
  4. 5-7HEAVEN

    5-7HEAVEN Guest

    :cool: You and i have the same idea about simply swapping one sprocket at the jackshaft to make drastic gear ratio adjustments. what you need to research is at what rpm your engine is most happy with at cruising speed, and at what rpm it's making full power without self-destructing.

    that's what Dave Staton does, with his 18.75:1 gearing. at this starting point, one could possibly find optimum gearing with maybe 2 sprocket changes.