crank won't rotate all the way

Discussion in 'Mechanic and Repair' started by kogafortwo, Jul 24, 2008.

  1. kogafortwo

    kogafortwo LawnSite Member
    Posts: 85

    Just scored an old Troy-Bilt Super Tomahawk 10 hp chipper for $100. Found it in a guy's back yard when I went there to pick up something else he had for sale and offered him cash. It's an early 90's model with the Tecumseh I/C and it is built like a tank. It has the original manuals, leaf tamper, an extra screen, and a brand new spare chipper blade. He even threw in some free cockroaches living in the debris in the chute. :laugh:

    He said it shook a lot the last time he ran it a few months ago. Then it got real noisy all of a sudden so he shut it down immediately. Now you can turn the crankshaft over not quite a full revolution, unless you really force it.

    I suspect a slightly bent crank. I plan to pull the recoil cover and cylinder head and rotate the crank by hand looking for any play of the conn rod or visible run-out at the flywheel. Any other ideas?

    I already found some threads on here that talked about crankshaft straightening so I will talk to my local small engine shop about that as soon as I get the engine torn down to the short block and figure out what's going on.
  2. mowermankevin

    mowermankevin LawnSite Senior Member
    Posts: 270

    Hey Coga, Do you know for sure it's the engine crank? I had a chipper given to me and it turned out the bearing on the chipper shaft was frozen, that's why I'm asking, do you have a belt drive to the chipper shaft,or is it clutched? Just make sure the engine is disconnected from the chipper. If it is and the crank still won't turn, pull the spark plug and squirt some lube in the cylinder and see if the piston is stuck from setting up for who knows how long,if it won't turn easily, don't force it, let the lube work for a day or two and try it again,gently. Sounds like rust stuck it.
  3. kogafortwo

    kogafortwo LawnSite Member
    Posts: 85

    It is a belt drive and the engine crank is truly hung up. The chipper shaft turns OK. I will definitely try the lube in the spark plug hole first. I am hoping that I can get it going without having to split the case and pull the crank.

    Thanks for the tip.
  4. Fisher40037

    Fisher40037 LawnSite Member
    Posts: 36

    I would suggest just pulling the head off first. I seriously doubt it is a
    bent crank.


    FIXDISS LawnSite Senior Member
    Posts: 445

    If the flywheel is stopping or binding at the same spot on every revolution then you may just have rust build-up on he flywheel magnets and coil shoes. Just went thru this with 2 different 6.5 hp Tecumseh's with horizontal shafts. Your vibration issue could be in the chipper itself so if you can isolate the engine by removing the belt you should be able to determine the source of the vibration. That's just my half-fast opinion. :hammerhead:
  6. khouse

    khouse LawnSite Bronze Member
    Posts: 1,465

    Sounds like a broken rod to me.
  7. BigFish

    BigFish LawnSite Gold Member
    Posts: 3,262

    Ain't no bent crank... I second khouse' broke rod.
  8. DiyDave

    DiyDave LawnSite Bronze Member
    Posts: 1,695

    I'll third the notion that its a bent or broken rod.:cry:
  9. kogafortwo

    kogafortwo LawnSite Member
    Posts: 85

    I was packing up my gear last night for today's after work lawn jobs, and I finally took a few minutes to pull the spark plug and look inside with a flashlight. The spark plug is way offset so I could not see the piston, but I did see a chunk of something that looks like WOOD. :dizzy:

    I have zero clue how a chunk of wood or whatever it is could get in there, even if the last owner ran it with no air filter. Whatever it is, there's more of it that is stopping the piston travel near TDC. Also, when I rotate the crank back and forth a few degrees where it binds up, it feels like there is some play and some noise. I'm hoping it's just the junk in the chamber getting rattled around and it only feels like "play" becasue cranks rotate easier near TDC anyways.

    I should find time to pull the head this weekend and get a real look. Still hoping for a top-end job only, even if the valves need lapping and lash setup.
  10. khouse

    khouse LawnSite Bronze Member
    Posts: 1,465

    Your probably looking at a valve head. Sounds like what we call "dropped a valve". Yes pull the head and look. I'm sure there is cylinder damage in addition to head and piston damage.

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