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  1. #1
    thompsdw's Avatar
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    Valve Lapping Question for Experts

    I am just going over the head on my 2003 155 GTX. When I lapped the first exhaust valve, I noticed that the seating surface was much larger than the last time that I lapped another head. Does anyone know if the seadoo valves have a double bevel that should cause a relatively small seating area, or if they seal over most of the valve seat flat?

    I know high performance car engines try to seal over a much smaller seat, but I am not sure if the Seadoos are that way or not. This is not a high hour engine - about 80 hours on the ticker. Any help is appreciated. My daughter is giving me performance reviews to get this ski back on the water.


  2. #2
    Moderator beerdart's Avatar
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    VALVE SEAT CONTACT WIDTH
    NEW
    Exhaust 1.25 to 1.55 mm
    (.049 to.061 in)
    Intake 1.10 to 1.30 mm
    (.043 to.051 in)
    SERVICE LIMIT
    Exhaust 2 mm (.078 in)
    Intake 1.8 mm (.07 in)

  3. #3
    thompsdw's Avatar
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    Thanks beardart. I watched a video recently that showed to use a permanent marker after lapping to determine the contact width versus the lapped surface. Thanks for the specs. I didn't remember seeing this in my manual.

  4. #4
    As a general rule, you get better sealing with a very narrow seat. However, if the seat is too narrow, you don't get good heat transfer properties (to cool the valve), and you risk damaging (pounding) the valve face due to the extreme pressure of a narrow seat.

    The big problem with these engines is carbon buildup on the exhaust seats. (every 4-TEC I have ever disassembled had some buildup on the exhaust seats, or erosion from too wide seats) On the N/A engines, I think you want to have a very narrow seat.

  5. #5
    suck my wake's Avatar
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    You want more seat width on the exhaust valves since they need more cooling than the intakes, especially on the s/c motors. The intakes get cooled by the incoming air/fuel mixture the exhaust needs to transfer that heat to the head .......

  6. #6
    Quote Originally Posted by suck my wake View Post
    You want more seat width on the exhaust valves since they need more cooling than the intakes, especially on the s/c motors. The intakes get cooled by the incoming air/fuel mixture the exhaust needs to transfer that heat to the head .......
    True, but read my post again. Too wide of a seat and you will be re-doing the head like every year due to carbon buildup and erosion, especially on a N/A motor, which is what the OP has.

  7. #7
    thompsdw's Avatar
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    Im going to measure tonight, I was just surprised that the lapping mark was so wide on a ski with 80 hours. My grease lapping compound was only medium, I cant believe the head has erroded that much. Instructions say to replace the head if it is too wide.

  8. #8
    thompsdw's Avatar
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    Well, Im damn close to 2mm. That amazes me for a head with this little wear and few hours. The lapped surface did have some pitting, but most of it is gone. Is the only way to fix this a new head, or will new valves repair the contact surface. Don't the valves wear before the head???? Help???

  9. #9
    mac_man_luke's Avatar
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    3 angle valve job and new valves

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