Valve seating issue - need help.

Discussion in 'Mechanic and Repair' started by Jason Pallas, Mar 2, 2012.

  1. Jason Pallas

    Jason Pallas LawnSite Bronze Member
    Messages: 1,335

    Ok. I'm working on a Kawasaki FB 460 / 12.5 HP (single cylinder). I'm trying to make sure the valves are set properly. The manual says that the valve width gap should be between .0039 - .006. Am I understanding this right? At top dead there should be a gap in the seating of the valve??? I thought that at TDC the valves should be completely seated and shut. Isn't that how a combustion chamber gets max power?
    Someone please tell me if I'm wrong here. The engine won't start, sputs and backfires through the carb and muffler and sure acts like there's a valve issue. Everything else is in spec on this engine. I've put in new valves in and lapped the valve seats. Everything looks good except this valve seating issue.

    Is this true? Should there really be a gap in the valve and valve seat at TDC of between .0039 and .006? Or should the valves be completely sealing the combustion chamber?

    Thanks guys.
  2. unkownfl

    unkownfl LawnSite Gold Member
    Messages: 3,837

    Valves need to be closed. What they're talking about is the width of contact the valve needs to see on the seat to valve face. Also, you could be referring to the lash set by grinding the actual valve stem. The lifters are solid so you have to do the adjustment by actually grinding the valve stem itself. Have you checked compression? Back firing probably means the valve lash is to tight.
  3. Jason Pallas

    Jason Pallas LawnSite Bronze Member
    Messages: 1,335

    Ok- thanks, that's sort of what I thought! Otherwise a compression test wouldn't yield too much and a leak down test would be useless right!?!? The clearance between the tappet and the valve is Ok on one valve - the other needs to be ground a little.

    So, I guess I'll make sure that both valves seal at TDC and then adjust the lash by grinding the valve stems so that they're both within tolerances correct?

    Thanks again for the help.

    Boy - this makes me appreciate OHC! LOL
  4. unkownfl

    unkownfl LawnSite Gold Member
    Messages: 3,837

    You're correct. Good ole flat head.
  5. Jason Pallas

    Jason Pallas LawnSite Bronze Member
    Messages: 1,335

    One last question: In the manual,when they refer to the "STD valve seat width" (.0039 - .0063), what are they talking about?

    Thanks a million for the help. Again!
  6. T-Trim

    T-Trim LawnSite Member
    Messages: 204

    std is short for standard. the valve seat is the shine face on the block. oh and if you need to reduce the lash on the valve. lap the valve and seat. but if you need to increase the lash grind the stem of the valve. be careful if you don't have a machine to do valve work.
  7. jsslawncare

    jsslawncare LawnSite Bronze Member
    Messages: 1,673

    1.Make sure you're on the compression stroke.
    2.Use a feeler gage to adjust the intake to .004 Don't worry about the .0039- you don't have a feeler gage for that.
    3.Adjust the exhaust to .006- All adjustment must be made with the engine cold.
    If the valve face or the seat face angle is off you should really carry it to a machine shop and let them do a valve job. By the time you buy everything to "lap the valves in" you could just pay them to do the job and with out question it would be right. Good-luck.
  8. piston slapper

    piston slapper LawnSite Platinum Member
    Messages: 4,337

    Js...adjust (grind the valve stem) the valves to the proper clearances first.
    Then....lap the valves to see how well the valve faces and seats are mating.
    The dull areas on the seat and the face will be your seating area.
    You have 3 angles cut on the valve seat to adjust the width and location of the contact area. most people don't have these tools ,so don't worry about it.
    A Kawasaki service manual should cover the specifics

    FB460's are one of the toughest and most forgiving engines in the industry.
    Get it close and it will run for a long time.
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  9. cgaengineer

    cgaengineer LawnSite Fanatic
    Messages: 15,778

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  10. piston slapper

    piston slapper LawnSite Platinum Member
    Messages: 4,337

    Hmmmmm...........snake oil for valves.........a whole new market......Hmmmm.....
    Back to the drawing board.
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