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flywheel key

Discussion in 'Mechanic and Repair' started by Lawn Sharks, Nov 29, 2002.

  1. Lawn Sharks

    Lawn Sharks LawnSite Senior Member
    Posts: 394

    Okay, at the risk of sounding like an idiot I was hoping someone could explain this to me. In a few other threads people explained a problem with the flywheel key "dislocating shoulders" and "pulling muscles". I am probably not thinking straight but what the heck does that mean. If a flywheel key drops out wouldn't the flywheel just free wheel? Wouldn't it be easier to pull? Help me out on this as I am totally confused.
  2. ksland

    ksland LawnSite Senior Member
    Posts: 927

    When a flywheel key breaks or lets go it changes the ignition timing which could cause it to fire before the compression stroke finishes which will rip the cord out of your hands, and if you hold the cord tight it will rip the next closest thing.

    The flywheel is pressed onto a tapered shaft which would make it still spin just not be located in the right position.:D
  3. Richard Martin

    Richard Martin LawnSite Fanatic
    Posts: 14,700

    If the key drops out (not actually possible, the flywheel is on top of the motor, not the bottom) or is sheared off then the flywheel would have spun making the mower impossible to start.
  4. Lawn Sharks

    Lawn Sharks LawnSite Senior Member
    Posts: 394

    but why would a freewheeling flywheel "dislocate a shoulder" ??

    seems to me if it had no key it would be quite simple to pull since you weren't pulling against anything
  5. khouse

    khouse LawnSite Bronze Member
    Posts: 1,465

    the flywheel bore is tapered and the cranks is too. we are talking not of the flywheel spinning but moving a little. if the flywheel if torqued a little tight can hold on it's own for some time without a key. some of the guys who race briggs and techumseh's put valve lapping compound in the flywheel bore and tighten it down in different positions to achieve optimal timing. they run at 6500 rpms that way.
  6. Lawn Sharks

    Lawn Sharks LawnSite Senior Member
    Posts: 394

    So, if I am to understand correctly it is a timing issue and premature combustion that will cause the sore muscles.
    I think I have a different problem with a 14hp Honda as it definately does not "rip it out of my hands" but just seems like it has a ton of compression and can be a real bear to pull at certain times. Will run some tests without a plug to see if it is compression related.

    Thanks to all!
  7. khouse

    khouse LawnSite Bronze Member
    Posts: 1,465

    we tried to figure out a kohler doing the same as yours. look for the "kohler evil starting beast" on the first page and maybe it will help.
  8. Doc Pete

    Doc Pete LawnSite Gold Member
    Posts: 3,469

    At least on the smaller motors, which can still cause a big problem, the key is soft and usually doesn't shear off, but does "begin to shear" and throws the timing of a few degrees. With the timing off, the machine wants to backfire, and will easily put the starter handle right out of your hand. The bigger problem with the larger motors is valve clearance "basically" causing the same "simulated" problem, and again, makes the motor backfire and pull the handle out of your hand. Single cylinder Kaw's are famous for this. As far as keys, if the key was hard, you'd probably start breaking cranks when you hit something with the blade......
  9. ksland

    ksland LawnSite Senior Member
    Posts: 927

    May also just be refering to countless pulls trying to start the motor afterwards. Before realizing the key is broke. That will sore your muscles.
  10. Fish

    Fish LawnSite Member
    Posts: 139

    The key doesn't hold the flywheel in place or keep it from "freewheeling", it just keeps the flywheel in place while
    tightening the flywheel nut.

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