SBT Jetski Engines, Parts & Accessories

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  1. #1
    Joined
    Aug 2001
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    Q I have been afraid to modify my 951 based on some stories I have heard of seized motors and water ingestion.

    A Other tuners may not agree with us on this but practically every seized and scored top end attributed to water ingestion has been a direct result of a head gasket failure to seal. We have seen countless cases where a GTX or a 3 seater has been riding on smooth water with no water leaking from the head pipe or entering into the hull. You would have to be continuously ingesting water for a period of time for this to take place. It would have to be at top end speed, otherwise you would sense the water at lower speeds. Sea Doo used o-rings to seal all previous engines. The 951 uses a metal gasket. Here is what happens. The metal gasket does not allow compressibility at or after installation. In other words, once the engine heats up and cools down a few cycles, the studs and bolts recess and lose some ability to compress the gasket to factory specs. We must remember that the base gasket is compressible and the thru studs go into the case. Any loss or settling of the gaskets and fasteners decrease the head gasket seal. The typical 10 hour service does not see the head bolts re-torqued. If they were re-torqued, you would see the paint chipped from the nuts and bolts on the head. YOU MUST LOOSEN the fastener first and then re-torque to specs. If you check torque without loosening first, you will achieve torque specs without tightening the fastener. The paint on the bolts and nuts will increase the holding of the fastener and give a false reading. Most engines see a 45 degree turning of the head fastener with a few fasteners turning a full 90 degrees before reaching specs.
    The 951 Sea Doo's have more water pressure than previous models. What happens is at higher speeds, when the engine is at or near full throttle, the water pressure actually forces some water into the combustion chamber. The engine can tolerate small doses of water, but this water literally steam cleans away the lubrication. When the amount of water is greater it will also start to show up as a decrease in top speed RPM, or a 'laying down' feeling at top end. It is not uncommon to see one perfectly good piston and one very badly damaged piston. Unfortunately, most of these incidents are routinely diagnosed as water ingestion through the carburetors and not thru the head gasket. When you back off the throttle slightly, the water pressure drops. What happens now is small amounts of combustion gas enter the water jacket. This could lead to localized hot spots which increase the likelihood of a larger head gasket leak. If we had visible bypasses, we might pick this up as air bubbles or intermittent water flow through the outlet.
    We have plenty of customers with many hours on their 951's with our kits. The head gasket problem never occurs if you re-torque every 30 hours of operation.

  2. #2
    Joined
    Aug 2001
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    80

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    could this indeed be a head gasket problem also, instead of exhaust gasket leak?

  3. #3
    Joined
    Feb 2001
    From
    Clearwater, FL
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    7,358

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    I'm sure a certain percentage of failure are due to blown head gaskets, and probably went mis-0diagnosed by less-than qualified dealer personnel. It is, however, easy to spot a blown gasket compared to water ingestion through the intake. I can't speculate as to whether or not the 951 has any higher percentage of blown head gaskets than any other engine, however we at least, do not see this with ours. We don't diagnose cores, so I can't say as to the originals.

  4. #4
    Joined
    Feb 2001
    From
    Florida
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    33

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    "It is, however, easy to spot a blown gasket compared to water ingestion through the intake. "

    Can you elaborate on this please?

  5. #5
    Joined
    Feb 2001
    From
    Clearwater, FL
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    7,358

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    It's easy to see the scoring and gouging patterns on the piston sides, cylinder walls, piston tops, etc. - to look look for blow-by from the combustion chamber to waterjackets, you can see evidence on the gaskets (when applicable), the head, the cylinders...they look very different in most cases.

  6. #6
    Joined
    Mar 2001
    From
    New Brunswick, Canada
    Posts
    51

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    Sounds reasonable that the head gasket would cause this.

    Is there a better head gasket that can be used other than the stock one?

    I don't have a shop manual yet, can you tell me what the torque spec and bolt tightening sequence would be for a 98 XPL?

  7. #7
    Joined
    Feb 2001
    From
    Clearwater, FL
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    Ours are OEM copies - we certainly do not see this trend.

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