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Engine HP required for running Doubles

Discussion in 'Lawn Mowing' started by Bunton Guy, Oct 15, 2001.

  1. Bunton Guy

    Bunton Guy LawnSite Bronze Member
    Messages: 1,917

    I was wondering what kind of engine you have to be running for doubles. I was wanting to put them on the 36" Gravely with a 12hp Kohler. Do you need a special settup or holster for the 2 blades ? My mower has that coupler type thing that is a plate that holds the blade to the spindle. Will the doubles bog down the motor. Will it require more greasing (dosent gravely have sealed bearings in the spindles ? ) Can you do doubles on a 21" walk behind ? is there limits ? What is best combo for sucking the grass up and chopping. The problem I have is the mower cant suck the grass up straight enough to give it that good even cut across it leaves to many straggler peices of grass.
  2. Richard Martin

    Richard Martin LawnSite Fanatic
    Messages: 14,699

    I really hope you just got this mower! In my opinion the 12 is just not quite enough to spin doubles. I had a 12.5 Kaw on my Exmark 36 and then I replaced it with a 14 Kaw and it just seems to be much happier with the additional hp.

    Your mower has what they call a saddle to hold the blades. You should pull the saddle off (it's held in place with allen screws) and replace it with a Gravely flat saddle. They do make it, I don't have the part number but they do make it.

    You should use a high temperature grease in the spindles if they are getting hot.

    Your Gravely should be cutting grass great. The 36" is a good mower. Have you sharpened the blades recently?
  3. Eng Mwr Guy

    Eng Mwr Guy Gravely Manufacturer
    Messages: 249

    In my opinion, a 12.5 motor is a little light for doubles.

    Depending on the age of the mower you should have maintenance free spindles i.e. no greasing required.

    Why not triples? (my smart a** answer to Is there a limit?)

    Listen to Richard M. He used to have a Gravely and knows what he is doing. Or go to a Gravely dealer to get some help.

    Let me know if I can help.

    Gravely Guy
  4. Bunton Guy

    Bunton Guy LawnSite Bronze Member
    Messages: 1,917

    I just bought it recently. It has a rebuilt motor and new carb. The blades are farely sharp they will be sharpened before I use it on anyones yard. The 12 hp is enough for what I am using it for I wont change out motors till it really needs it. If I cant run doubles then I wont.
  5. dlandscaping

    dlandscaping LawnSite Senior Member
    from mass
    Messages: 835

    i have doubles on my toro 36 fixed and it has a 12.5 kaw engine, boy it does a number on them leaves and leaves a nice stripe. it sounds like plane is taking off when you turn those blades on!
  6. Eric ELM

    Eric ELM Husband, Father, Friend, Angel
    Messages: 4,830

    I don't know if this will help or not, but I ran doubles on 2 different 20 HP Magnum Kohlers on 60" Choppers. That is just 8 more Horse Power but 24 more inches of cut.

    12/20 in HP would be 3/5
    36/60 in cut would be 3/5

    According to that, you should have at least as much power as what I had for your cutting width.
  7. Flex-Deck

    Flex-Deck LawnSite Silver Member
    Messages: 2,845

    I have a JD 455 with a 78" 4 spindle deck and am running gators on top and dixie choppers on bottom (8 blades total) and am running 10 mph and mowing neat with a 22 HP yanmar diesel.
  8. vipermanz

    vipermanz LawnSite Bronze Member
    Messages: 1,773

    i run them on a 6.5 hp mower with no probs
  9. I put doubles on my 36" Byers Gold and it really improved the quality of cut. It improved the amount of lift tremendously.
    Stock blades on the bottom and Gators on the top. It does add a noticible load on the motor, but I have a 14 hp Kohler, belt drive and no sulkey, so I still have plenty of power.
  10. Charles

    Charles Moderator Staff Member
    Messages: 8,822

    NOw I dont know if this caused it. But I ran doubles off and on using a 23 hp pro and the pto belt wore out within 300 hrs. This belt was not cheap and not cheap to have put on and there was no telling how long it was effecting the cut with the slipping the belt was doing before it finally shredded. I could see where doubles would cause more wear on the belts in a short time though

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