Think my ZTR is going to mower heaven...

Discussion in 'Mechanic and Repair' started by PipeHitter, May 25, 2008.

  1. PipeHitter

    PipeHitter LawnSite Member
    Posts: 13


    Have a Bobcat ZTR 60" w/Kohler 22hp at 500hrs.

    Just started cutting and made about two passes when the engine sputtered out and died, like when you get off the seat with the PTO engaged.

    I started it backup and I hear a horrible knocking/tapping sound. Not normal, and very obvious. The type of sound that makes you want to shut it back down right now. Raising the throttle the engine wants to die and the sound get worse. I removed the air filter and the engine got stronger and would stay running, but the noise got much worse.

    I tried to limp it back to the house but every time I would take either one of the control arms out of the neutral slot (same slot you have to them both in to start the engine) the engine dies. So I towed it back to the house and let it cool down.

    Tried again, same thing. It will idle and the sound does not have a pattern but it is consistent. Gets worse with more engine speed. Motor seems to blow a little black smoke now, but maybe I didn't notice it before. And as above if I lift an arm out of neutral it dies.

    Oil was low, I topped off and no change.

    Any ideas? Thanks for any replies.
  2. PipeHitter

    PipeHitter LawnSite Member
    Posts: 13

    some additional info.....

    tried looking for a short someplace in the wire harness as the whole 'can't take the arms out of neutral' kept nagging me that it was electrical. I also noticed that I cannot release the parking break or the engine will die. Only other thing I could think to check was the governor, but it seems to be actuating fine.

    My fear now is the damage/noise is in fact internal to the motor, and substantial enough that the motor has some sort of fail-safe that is keeping the mower from being operated other than idle. :(
  3. LushGreenLawn

    LushGreenLawn LawnSite Silver Member
    Posts: 2,121

    Even if you had to replace an engine, its not worth trashing the machine. Escpicially with only 500 hours on it.
  4. chesterlawn

    chesterlawn LawnSite Senior Member
    Posts: 708

    Just a thought did you check the pto switch.
  5. PipeHitter

    PipeHitter LawnSite Member
    Posts: 13

    Well, I planned on taking it to the shop tomorrow when a friend I had over to help load it up convinced me to tear it down and take a look. This time of year the local shops are usually weeks behind anyway. I've got some experience with two strokes and single cylinder four strokes so I thought what the heck why not.

    Below is what I found. Looks like the valve stem seal munched and threw the valve and rocker arm off.

    Almost have the head off, still need to pull the carb, muffler and manifold. Getting tired so I don't want to start zoning and forget how it all goes back together.

    Any idea what caused this, and what could the extent of the damage be?



    FIXDISS LawnSite Senior Member
    Posts: 445

    Looks like the keeper came off the valve stem and the valve dropped onto the piston. Remove the spark plug from that cylinder and insert a small blade screwdriver into the hole then try to turn the engine by hand to see if you can feel the piston moving up and down. Most likely if the valve dropped into cylinder the you have major damage inside crankcase.Can you see the tip of the valve stem inside the spring ?
  7. PipeHitter

    PipeHitter LawnSite Member
    Posts: 13

    I'll check again tonight,,,you think there might be crankcase damage?

    I was thinking at the most:

    head: due to valve banging on/in it
    piston: due to piston slapping valve
    cylinder: due to broken pieces of valve scratching bore

    I didn't think there would be anyway for broken pieces to get down to the crankcase from the cylinder?
  8. Sharpcut 1

    Sharpcut 1 LawnSite Senior Member
    Posts: 450

    Save yourself some aggravation before you put it all back together and make sure your cam is OK. Put your pushrod on the lifter and take a 5/8 wrench underneath on the clutch. Turn the engine over and maje sure it's pushing the rod up all the way. I'm starting to see some cam lobes wear off and cause the noise, but yours was probably from the rocker arm falling off. If your lifters are'nt bleeding down, the pushrod will hang the valve up. Did the cylinder backfire when it happened?? May of been loaded up with fuel.
  9. PipeHitter

    PipeHitter LawnSite Member
    Posts: 13

    Sharpcut 1: Cam seems to be fine. No backfire just sputtered out.

    Got the head off, bore looks great with plenty of cross-hatch. There is some minor damage to the head and top of the piston as evident from the pics. Also looks like she bent a pushrod.

    From the pics, is that groove/cut portion of the valve normal? With the damage shown should I replace the piston and head? Or just the valve keeper, valve and pushrod and put her back together?





  10. jkilov

    jkilov LawnSite Bronze Member
    from MS
    Posts: 1,415

    Looks like the valve slipped off the retainer like FIXDISS said. The piston then knocked the valve back and forth causing the valve seal to break and also bend the pushrod. Or it was the seal that broke first causing the valve to slip off the retainer. Hard to tell which happened first.

    The problem is I see marks where the pieces of the seal were crushed between the head and piston. Hopefully the connecting rod is'nt bent and the bearings are OK. Can you feel any play at all whilst moving the piston ? Not good.

    If you can check this somehow and it's OK, you can get away with it relatively cheap (head, valves, pushrod, gaskets).

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