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2007 rxp 215
- Thread starter 1hsv1976
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devonte007
Active Member
Sounds like you are still experiencing cavitation. You state that the clearance between the wear ring and impeller is 1.5mm which is a lot. I believe the maximum allowable spec is 0.35mm before replacement, maybe a typo and you actually have 0.15mm clearance?
1. when you changed the wear ring was the impeller in good shape? Any dings, dents, etc. Excessive damage to the impeller will cause cavitation problems too.
2. If the new wear ring and impeller are in fact in good shape and within spec, then you need to look at the carbon seal which is the next logical step. You may be sucking air through the drive shaft seal which would mean replacement of the carbon seal and the rubber boot. Had to do this on my boat couple years ago and made a huge difference.
3. Also, when you put the jet pump back on the ski did you ensure the neoprene seal between the ski and the jet pump was in good shape? If not a bad seal could cause problems as well.
Here is a good thread that explains in detail how a 'jet pump works'. Helped me a bunch when I was diagnosing my cavitation problems http://www.seadooforum.com/showthread.php?4958-quot-How-a-jet-pump-works-quot&highlight=jet+pump+operation
Hope this helps a bit, good luck and let us know what you find out.
1. when you changed the wear ring was the impeller in good shape? Any dings, dents, etc. Excessive damage to the impeller will cause cavitation problems too.
2. If the new wear ring and impeller are in fact in good shape and within spec, then you need to look at the carbon seal which is the next logical step. You may be sucking air through the drive shaft seal which would mean replacement of the carbon seal and the rubber boot. Had to do this on my boat couple years ago and made a huge difference.
3. Also, when you put the jet pump back on the ski did you ensure the neoprene seal between the ski and the jet pump was in good shape? If not a bad seal could cause problems as well.
Here is a good thread that explains in detail how a 'jet pump works'. Helped me a bunch when I was diagnosing my cavitation problems http://www.seadooforum.com/showthread.php?4958-quot-How-a-jet-pump-works-quot&highlight=jet+pump+operation
Hope this helps a bit, good luck and let us know what you find out.
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From a fairly new member, you seem to have learned quite a bit since joining. That doesn't reflect on your mechanical ability before you even joined. While reading your reply, I clicked your link. I kinda laughed because it's been so long, I kinda forgot about writing it. But, it is still up to date and accurate.
Your advice to him wasn't only solid, but the layout was really easily understood. If I might add just a couple things, the maximum clearance is .040"... I don't keep up with the metrics, but I think it equates about .75mm.
Like you stated, if he's removed the pump, did he get a good seal at the hull at re-assembly, and is the thru hull seal leaking air from the engine compartment? Last, and so often missed, did you inspect your stator vanes? For the pump to work as a compressor, you have a set of rotating vanes (your impeller) and a set of stationary vanes, or stators. If you picked up debris that was capable of changing the waters flow over those vanes, it will cavitate. I see this usually when a rock is picked up close to shore and wedged between the impeller and vanes. Sometimes, when you try to look from the back with a flashlight, you won't even see it. So, sometime, it's best to do a thorough inspection.
Also, if your grease cup ran dry and you've lost your shaft clearance, the shaft will wobble the impeller and chew away a bit of impeller clearance.
Last, (yeah, I always save the good stuff for last)... what it would be like to be 20 years old again and behind the wheel of my Camaro with my small block 400 cubic inch that I built from the ground up. Power, power, power. These skis have come a long way since the 85 and 110 hp motors of the XP's and GTX's. Since I've already wrote a book, I'll get to the point. When I first got my Camaro (1968), it had the standard 327 engine. When the light turned green, I could nail the throttle and speed off from the light. If I were racing someone in say, an Impala, with the same motor, I'd win. Reason being, my car was lighter. But, if I a more powerful engine in my car (the 400), when the light turned green, I spent the first 3 seconds burning rubber. It gave the Impala the edge to beat me. You can also see this in drag racers. If they don't do a burn out to heat up their tires, they won't stick to the pavement and will break traction and lose.
In saying all that, in effect, I believe (and only an opinon of mechanical theory), the horsepower being generated by these 4-TEC, supercharged motors is so great, the speed of the impeller is actually able to "skip" or slice through the water. In essence, spinning it's wheel before it grabs (or creates nozzle pressure). In my old 2 stroke, it spins up fairly slowly compared to your 4-TEC, creates nozzle pressure and blasts me to top speed pretty fast. I might have a small air leak around my pump or hull seal. But, because I don't have that power, I don't have to worry about such a small infraction. From a different perspective, you can look at what your compressing to make thrust. The viscosity of the water could (and I'm really speculating with logic here) play a role here too. If you ride a 4-TEC up north, where the waters around the New England states are cold year round, the water is more dense, giving the impeller something heavier to bite into. If you live in south Florida, or lower toward the equator, water is less dense because its warmer. This same thing is true with the gas turbine of a jet aircraft, which also works on the compressor principle for thrust. The higher the altitude, the lighter the air, the harder the engine has to work to maintain thrust. That is why they have a limited ceiling too (outside the fact the oxygen content of the air is less, which you need for combustion).
So, your propblem could also be nothing more than your ski's design to bite the water at initial thrust. Yeah, it's meant to do that, but that was when it was new. In the high performance motor, it only takes something minor to take away that ability to operate at peak performance. You also have to remember, salt water contains dissolved oxygen (along with Hydrogen) which can gas out and help perpetuate cavitation, if only for a split second. With the 215-255 hp motors, thats a lot of room for error.
1.5mm is approx. .06 inches. I'm not sure if you added an extra "0" by mistake but I figured it might be worth mentioning...
red2blue
New Member
Eh....earlier I'd left out a 0.
The gap between my prop and ring reads between .004-.006
Yeah, tight....real tight.
.004" = 0.1016 mm ....15 times tighter than the thread starter.
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No, you said it how you meant it and didn't leave out a 0. I figured it'd be worth while to confirm the number or if it was a typo, since a .040-.060 would've happened to be consistent with the original poster. I agree that 1.5mm is huge. Most of my props won't spin free by hand after first install.
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