How tight is the impeller supposed to be once installed into the wear ring??

[jtelep]

Hi all,

I've got a unique situation developing here that's been a problem for at least the last 2 impellers (hopefully not the 3rd one too). I was told that I needed a new impeller as the wear ring was replaced so I purchased a reman from SBT and when it came I installed it and instantly noticed that it spun free on the wear ring. I put it all back together and tried it and just as I thought I was cavitating like crazy. I took the pump to a local shop where I was told that there should be no light coming from around the edges of the blade against the ring (which in this case there was). I called SBT and told them what happened and they shipped me another reman impeller. I just received it and put it back in the pump now without tightening it to spec but hand snugging it on there I noticed this time this was the first one to actually touch and put marks in the ring however just at the very edge of the blades. Does it have to be all the way around or it is just the very tip (like last part of the blade) that is supposed to touch the ring? One guy told me that if I can fit a couple of business cards in between the ring and impeller I am OK but the last thing I want to do is reassemble this thing and get it all the way back to the lake for the same result.

Any advice would be greatly appreciated.

Thanks!!!

 

[Strizzo]

it should be close, but doesn't have to be exactly touching the wear ring to be adequate. since you are describing severe cavitation, i'd say you either have a leak at the carbon seal if your ski has one, or there is a leak from somewhere else, like between the pump and hull or ride plate and hull seal. did you replace the neoprene ring when you changed the impeller the first time?

 

[jtelep]

I was told that if you can see light coming from around the edges of the blade that there is too much room and it will cavitate. My question is if the very edge of the impeller (i.e. like the last few centimeters of the blade) is in contact on 2 out of 3 sides and is actually now "wearing" the ring which incidentally this is the first impeller to leave marks on the ring, is that tight enough? I did replace the neoprene seal when I pulled the pump the last time I did this so I know that can't be it and since it's a '95 XP it doesn't have a carbon seal (right?)

 

[Linescreamer]

Dude. There is a spec in the manual for Maximum clearance. Most are like 1mm and yes the Impeller should spin freely.

 

[Dennis]

To answer your question,

typically just the leading tips of the impeller blades will be touching the wear ring. In other words, the majority of the impeller blade will NOT be touching.

 

[Dr Honda]

In the ideal situation... NOTHING should be touching. Spec is up to a 0.040" gap between the ring and impeller.

The shop that said that there should be no light coming though are idiots.

If it's close, and you still have cavitation... it's from an air leak. Most likely... the drive shaft seal.

 

[jtelep]

If the seal or boot it bad you wouldn't know it until you took the whole thing apart would you? I am curious because I've seen videos of the opposite happening then what happened to me and that's that when the jet pump was taken off the drive shaft stayed in place. Both times I've removed my jet pump the drive shaft came along with it. Would that be a sign of a bad boot or seal? I mean the drive shaft simply seems to slide in and out of the flywheel side with nothing holding it tight on the flywheel end. Is that normal or should that end be holding the drive shaft in tight in place even when the jet pump is taken out?

 

[Dr Honda]

You have an old style seal, so there is nothing holding the drive shaft in the hull. On a "Carbon Seal" system... the stainless ring wont allow the driveshaft to come out... unless you remove it's clip.

If the driveshaft is out... remove the seal pack, and inspect it. If the seals are in bad shape... then rebuild it.

 

[jtelep]

Ok that's great. So following up to that my next question then would be if the seals are in bad shape would that cause the boat to cavitate worse than if the impeller wasn't coming in contact with the wear ring? I'm just trying to figure this all out before I take it back to the lake again. Thanks.

 

[Strizzo]

Ok that's great. So following up to that my next question then would be if the seals are in bad shape would that cause the boat to cavitate worse than if the impeller wasn't coming in contact with the wear ring? I'm just trying to figure this all out before I take it back to the lake again. Thanks.

yes. its like trying to drink through a straw with a hole in it.

 

[jtelep]

I'm sorry I'm a dork but I'm trying to understand how this works. This is not a sealed system. The driveshaft simply turns the impeller which then sucks water in through the intake grate which then gets pushed past the impeller causing thrust. How do bad seals at the flywheel end of the driveshaft cause cavitation?