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.
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.
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