Rabid
Active Member
This is quote Bell's that I came across on another post about changing crank case oil. I did see on my engine that it was a rebuild and it made me wonder about the 3/4 throttle cruising. I also was wondering what else I need to watch out for?
Posted by bills86e
Being this post is on the '98, Here is a write by a Famous Seadoo Industry Leader BILL O'NEIL, Watercraftmajic, California:
Do not look at the prices for the FI hoses without a cardiologist standing nearby.
The 1998 947 engines were the ones that would lose the mainbearings up front behind the flywheel. They had plastic cages in them.
All Elko pistons are subject to skirts breaking off as they will bend inward when water gets trapped between the skirts and the clyinder liners. They slap for quite awhile before they break off and if you ignore the slapping pistons, you deserve what you get when they break.
Oem quality bearings and seals should go into any 947 rebuild. Caged wrist pin bearings do not belong in any recreational 947 engine.
The main reason I spent so many hours at the lake testing filters and rejetting specs is to eliminate premature piston failures, the extra rpm and speed was a by product of feeding the motor the fuel it needs to run cooler and to build more power, with a much richer upper midrange fuel curve.
In 1997.5, you did not even want to attempt to cruise at 3/4 throttle with the 947 engine as the leanest part of the fuel curve was just below full throttle. It would almost guarantee a piston failure in at least 50% of the prototype grey deck GSXL's.
Fortunetly, Sea Doo added piston to clyinder wall clearances, bigger carb jets and needle valves, lower PO pressure and they turned the carbs 180 degrees in 1998 after replacing way too many top ends for free.
Forged pistons will hold up to some slapping for quite awhile, whereas the die cast Elko pistons will not hold up very long with a slapping piston or two.
Alot of rod failures are because idiots try riding the boat above idle speed right after rolling it over or swamping it and not removing the sparkplugs to pump the water out of the bottom of the motor. The water gets sucked up into the combustion chamber at higher rpm where the piston can hydrolock and bend the rod below it. Most riders do not realize it when they have lost a couple hundred rpm and they continue to ride the boat normally with a bent rod in it. The next thing you hear is a huge clunk and the motor stops turning. The rod will break half way up the rod and the lower piece will puncture the cases and usually wipe out at least the reeds and the surrounding aluminum reed opening. I have seen them break the starters off and ruin that side of the cases too. I cannot express how many 947 rust bucket engines we see each year in the shop with rods hanging out of them.
IMO, most of the above, other than the plastic ball retainers in the bearings, and the tendency to sieze pistons at less than full throttle when the 947's were introduced, are the owners or the riders fault.
Take a lightweight aluminum casting and put a 78mm crank in it and 88mm pistons on it, producing about 130 hp out in the water where it is vunerable to having water enter it, and you have the perfect storm. 130 hp in a recreational package that small and lightweight is a really big deal if you think about it.
Does anyone remember Sarge who has spent the past 15 years on misc forums ? He had a 1996 XP and then a 1998 XPL. He was retired military and spent almost every warm day riding his watercraft on a river in Connecticut. The last time I heard he had over 350 trouble free hours on his 947 engine, and I believe about the same on his 787 engine. He is now trying his best to wearout an RXP 4 Tech engine. I sold him lot's of parts like the 947 rejetting kit and filters, Solas impellors and nozzels for his '96 XP and a few other gadgets. The key to his success was fogging and regular maintence and allways running an oem exhaust system.
My own 947's were all heavily modified and rarely got more than 25 -40 hours on them before I tore the clyinder off to replace the pistons and wrist bearings. But I did run the crap out of a couple of my big bore rec motors for quite awhile without breaking them before I sold them off a year or two later.
Posted by bills86e
Being this post is on the '98, Here is a write by a Famous Seadoo Industry Leader BILL O'NEIL, Watercraftmajic, California:
Do not look at the prices for the FI hoses without a cardiologist standing nearby.
The 1998 947 engines were the ones that would lose the mainbearings up front behind the flywheel. They had plastic cages in them.
All Elko pistons are subject to skirts breaking off as they will bend inward when water gets trapped between the skirts and the clyinder liners. They slap for quite awhile before they break off and if you ignore the slapping pistons, you deserve what you get when they break.
Oem quality bearings and seals should go into any 947 rebuild. Caged wrist pin bearings do not belong in any recreational 947 engine.
The main reason I spent so many hours at the lake testing filters and rejetting specs is to eliminate premature piston failures, the extra rpm and speed was a by product of feeding the motor the fuel it needs to run cooler and to build more power, with a much richer upper midrange fuel curve.
In 1997.5, you did not even want to attempt to cruise at 3/4 throttle with the 947 engine as the leanest part of the fuel curve was just below full throttle. It would almost guarantee a piston failure in at least 50% of the prototype grey deck GSXL's.
Fortunetly, Sea Doo added piston to clyinder wall clearances, bigger carb jets and needle valves, lower PO pressure and they turned the carbs 180 degrees in 1998 after replacing way too many top ends for free.
Forged pistons will hold up to some slapping for quite awhile, whereas the die cast Elko pistons will not hold up very long with a slapping piston or two.
Alot of rod failures are because idiots try riding the boat above idle speed right after rolling it over or swamping it and not removing the sparkplugs to pump the water out of the bottom of the motor. The water gets sucked up into the combustion chamber at higher rpm where the piston can hydrolock and bend the rod below it. Most riders do not realize it when they have lost a couple hundred rpm and they continue to ride the boat normally with a bent rod in it. The next thing you hear is a huge clunk and the motor stops turning. The rod will break half way up the rod and the lower piece will puncture the cases and usually wipe out at least the reeds and the surrounding aluminum reed opening. I have seen them break the starters off and ruin that side of the cases too. I cannot express how many 947 rust bucket engines we see each year in the shop with rods hanging out of them.
IMO, most of the above, other than the plastic ball retainers in the bearings, and the tendency to sieze pistons at less than full throttle when the 947's were introduced, are the owners or the riders fault.
Take a lightweight aluminum casting and put a 78mm crank in it and 88mm pistons on it, producing about 130 hp out in the water where it is vunerable to having water enter it, and you have the perfect storm. 130 hp in a recreational package that small and lightweight is a really big deal if you think about it.
Does anyone remember Sarge who has spent the past 15 years on misc forums ? He had a 1996 XP and then a 1998 XPL. He was retired military and spent almost every warm day riding his watercraft on a river in Connecticut. The last time I heard he had over 350 trouble free hours on his 947 engine, and I believe about the same on his 787 engine. He is now trying his best to wearout an RXP 4 Tech engine. I sold him lot's of parts like the 947 rejetting kit and filters, Solas impellors and nozzels for his '96 XP and a few other gadgets. The key to his success was fogging and regular maintence and allways running an oem exhaust system.
My own 947's were all heavily modified and rarely got more than 25 -40 hours on them before I tore the clyinder off to replace the pistons and wrist bearings. But I did run the crap out of a couple of my big bore rec motors for quite awhile without breaking them before I sold them off a year or two later.
