Help!!! cant figure this out.

Discussion in 'Mechanic and Repair' started by Travis1010, May 10, 2013.

  1. Travis1010

    Travis1010 LawnSite Member
    Posts: 102

    I have a grasshopper 720k with a kohler 20hp aircooled engine that began to overheat and run bad. I popped the valve covers off and all the valves are really tight no matter what. Ive called the dealer and he says he doesnt know what it could be.
     
  2. Travis1010

    Travis1010 LawnSite Member
    Posts: 102

    I forgot to mention i just got done putting fresh rings in and it ran great for the first 10 hours. I cleaned up the heads and all the valves looked fine. The wierd thing is all 4 valves are all about the same tight. They move about 1/8 inch when i unscrew the rocker. I need to get back to mowing any ideas are welcome!!!
     
  3. Patriot Services

    Patriot Services LawnSite Fanatic
    Posts: 12,536

    I'm thinking your valves need a proper adjusting. Its not about tightness but proper clearence between the rocker and valve stem. When the engine heats up this gap or "lash" decreases. It can decrease so much it will have zero gap and hold one or more valves slightly off their seats. This will cause the crappy running. Fresh rebuilds do run hot for a bit until everything seats in. Do you have an infrared heat gun? Hot is sometimes a relative term without an actual gauge to look at.
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  4. ericg

    ericg LawnSite Silver Member
    Posts: 2,558

    The Kohler 20HP engines have hydraulic lifters so there is zero lash at all times unlike a solid lifter that has specific settings for intake and exhaust lash.
    I have seen issues like you describe and many times the root cause is the lifters become pumped up and holding the valves open as Patriot pointed out. In many cases, this is due to dirty oil or extended oil change intervals. I would check your lifters and see if you can bleed them down. If not, I would replace the lifters and be back in business. By the way, the lifters from a small block chevy are the same as the Kohler lifters and much less expensive.
     
  5. Patriot Services

    Patriot Services LawnSite Fanatic
    Posts: 12,536

    Where's Slapper and Rob? They are the Kohler Kings here abouts.
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  6. Travis1010

    Travis1010 LawnSite Member
    Posts: 102

    ok thanks...i was running good 10w-30 in it so dont think it would be oil. I might try replacing them but the wierd thing is why they all did it at the same time. I tried compressing them but they wont go any more. The dealer did mention the chevy lifters would fit though. Thanks for the replies. I might have to get some lifters unless anyone else knows of anything else it could be
     
  7. ericg

    ericg LawnSite Silver Member
    Posts: 2,558

    make sure you soak the lifters in oil prior to installation.
    Follow the instructions in the Kohler manual referencing lifter installation and you will be fine.
     
  8. Oldtimer

    Oldtimer LawnSite Bronze Member
    Posts: 1,454

    Are You Using 10W30 Oil?
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  9. Patriot Services

    Patriot Services LawnSite Fanatic
    Posts: 12,536

    You need to do a little more than just soak them. Working the plunger a few times while immersed in oil will work. Another trick is a pump type oil can through the side oil fill hole. Lifters need to be filled prior to firing it up the first time. If you can't work the plunger at all then the bleed downs are plugged and non functional. Not too odd that they all go at once. You should always replace them as set anyways as they wear mate to the camshaft.
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  10. piston slapper

    piston slapper LawnSite Platinum Member
    Posts: 4,240

    Few questions....
    Why did you rebuild it in the first place...what was the failure..??
    Did you use a torque wrench on the rods..sump..heads..rockerarms...and intake..????
    Is there any silvery residue in the oil..???
    Were the heads resurfaced.???
    Did you install standard rings.???

    Do a compression test...and a leakdown test...
     

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