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Getting more ground speed from walk-behind

Discussion in 'Lawn Mowing' started by Wayne Offiler, Oct 28, 2001.

  1. Wayne Offiler

    Wayne Offiler LawnSite Member
    Messages: 113

    A couple of weeks ago, I mentioned that my Bunton 52' hydro wb topped out at about 5 mph, even after putting on larger drive tires. (I use a Proslide). Someone suggested that I put smaller pulleys on the hydro pumps (I think it was Mr. Stone).
    I could also put a larger pulley on the engine end. Either would spin the pumps faster, pushing out more fluid.
    Has anyone done this? Did it give you more speed?
    My main concern is that I might be putting more stress on the pumps than they were designed for.
  2. lawnMaster5000

    lawnMaster5000 LawnSite Senior Member
    Messages: 591

    thought about it but then decided exactly what you are concrearned about. so i never did, but i am sure that they can be spun a little faster. but also, make sure that theya re adjusted to use full capabilities, some mowers dont use the hydro pumps/motors to their full potential.
  3. MOW ED

    MOW ED LawnSite Fanatic
    Messages: 5,028

    Ask Engineer Mower Guy (aka Berry from Gravely). I demo'ed a prototype Gravely Hydro this summer that I'd swear did at least 10MPH wide open. I think they tamed it down a little on the production model.
    When your in the market, make sure you try one of these out , lots of great ideas incorporated in the new Gravely WB's.
    Good Luck
  4. Eng Mwr Guy

    Eng Mwr Guy Gravely Manufacturer
    Messages: 249

    Either increasing the size of the engine pulley or decreasing the sheave size of the input to the hydro pump would speed it up.

    Usually, the max input into the pump is 3600rpm but not always. You would need to get the specifications of the pump to find out what the maximum input speed should be. You can then play with pulleys and such. If you do not increase the pump speed past the design limit you shouldn't have any problem with more than normal pump failures.

    LM5000 is correct. It may be you are not getting full sweep of the hydro pump arm into the pump. If a linkage is hosed up or some kind of interference this could be the culprit also.

    Another, less often used way is to decrease the size of the wheel motors. This would decrease "power" while increasing speed. This would potentially cause hoses and such to be reexamized for pressure and the entire system should be looked at.

    The new Gravely Hydro, in the high linkage position does only 8.5mph. "Normal" from the factory speed will be 6.3mph.

    I did let Ed use the fire breathing dragon WB prototype #2 that was just a hair under 10mph. He even lived to tell about it.

    Gravely Guy
  5. scott's turf

    scott's turf LawnSite Senior Member
    from NH
    Messages: 949

    As a mechanical engineer and a landscaping company owner you could have a couple of problems trying to increase the spead of your mower. First of all the engines are designed for a specific torque setting. This is simply force X distance. The larger the pully, the less force required to due the same job. A simply example of this is trying to move your truck from a dead stop in 5 gear instead of 1st. The engine will stall. This may happen as well if you are going up a hill with your mower or you have a heavy rider hanging off the back. This continuing stress on the mower and drive components could lead to premature breakage. Companies would make their mower faster in a heartbeat if it only required changing the size of a pully. I am sure warrenties would be voided as well if a problem resulted from your modification.
  6. Eng Mwr Guy

    Eng Mwr Guy Gravely Manufacturer
    Messages: 249

    **I am sure warrenties would be voided as well if a problem resulted from your modification.**

    Of course. I assumed this unit was out of warranty.

    Modify at your own risk. Dealerships might not support you if the modification goes poorly and they have to fix your attempted mod.

    Gravely Guy
  7. TLS

    TLS LawnSite Fanatic
    Messages: 7,943

    How fast can you comfortably walk? This is why manufacturers make them only go 5-6mph. They dont count on sulky use. Plus most of these walkbehinds are too underpowered in the engine department to keep up with ZTR speeds while still cutting grass. If you did the larger tire size modification and your still not happy, then these other mods aren't going to make you much happier. My only other suggestion would be to increase engine RPM's. Make sure that they are AT LEAST 3650 NO LOAD. You can go higher, but I see entirely too many new mowers delivered spinning only 3450 RPM's.
  8. little green guy

    little green guy LawnSite Senior Member
    Messages: 955

    Put on smaller diameter hydralic lines, I did this on a scag and it made it alot quicker.

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