Impeller clearance question?

[Danosll]

Hi guys I have single 787 1997 challenger 150 psi compression . Appears to cavitate badly out of the hole. I have a new carbon seal and bellows very tight no water intrusion . Rebuilt pump and wear ring. Stock impeller without any nicks or dents. Motor revs to 7300 rpm. Have to back off throttle to plane. Here is my question. When I measure clearance with feeler gauge I have .020 at inside and outside tips but almost at limit at the center of the impeller. Again wear ring is new. Is this normal or has my impeller been reworked. Would that cause the over-reving/cavitatng. If I do need to change impeller what would be a good alternative to stock. I would want as much bottom end as possible. Thanks in advance Dan

 

[Coastiejoe]

.10 is the normal max from the wear ring to the impeller. Anything greater will decrease performance an allow cavitation depending on load.


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[Danosll]

Thanks for the quick reply. Is it normal to have a difference between center and tips of impeller my difference is almost.020 thanks

 

[Danosll]

And impeller looks perfect to the naked eye

 

[Coastiejoe]

If I understand you right. You are basically saying some blades are longer than others. I that is the case, then it has been works on. All blades should be equal. Not only for cavitation concerns, but for balance as well.

Another test is to pull the impeller and lay it on its hub. Put a long flat it across the top hub. Measure down to the blades. These should all be the same as well. If not, it is bent. And if it is bent, that can relate to a shorter blade. So that may actually be the issue in your case.


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[Danosll]

Thanks agin joe I wish I had taken pictures but I left boat AT cottage. When I measure each blade on impeller in pump with new ring with feeler gauge. I get about 0.020 at suction side tip. .038 at center. And .020 outlet tip. So the impeller blades are not concentric. But I'm still with in factory specs. But no hole shot. Just revs right up to 7300 rpm.

 

[Danosll]

I changed carbon seal and bellows

 

[Waterluvr]

So I'm working on the very same year and model myself (just acquired it) and have new carbon seal, bellows and all new parts installed in the pump housing ready for a new impeller as well. I was going to pick up the stock impeller new from the dealer tomorrow, is there a better choice to the stock unit for all around use? This is my first boat with a jet and I have been reading and gaining a lot of very useful information from the threads here so far.

Danosll I hope you get your issue figured out, sounds like you had pretty much the same job on your's as I did. Mine ran well when I got it but the previous owner had destroyed the pump wear ring and impeller on the rocks. It would build rpm but couldn't get out of it's own way.

 

[Coastiejoe]

So I'm working on the very same year and model myself (just acquired it) and have new carbon seal, bellows and all new parts installed in the pump housing ready for a new impeller as well. I was going to pick up the stock impeller new from the dealer tomorrow, is there a better choice to the stock unit for all around use? This is my first boat with a jet and I have been reading and gaining a lot of very useful information from the threads here so far.

Danosll I hope you get your issue figured out, sounds like you had pretty much the same job on your's as I did. Mine ran well when I got it but the previous owner had destroyed the pump wear ring and impeller on the rocks. It would build rpm but couldn't get out of it's own way.

Not sure who has what for boats, but generally speaking the SKAT impeller gives both a bit of low end performance as well as top end. Very little as far as whole numbers go but you will feel it in regards to performance. Basically, it will be more responsive.

 

[Sportster-2001-951C-Stock]

So I'm working on the very same year and model myself (just acquired it) and have new carbon seal, bellows and all new parts installed in the pump housing ready for a new impeller as well. I was going to pick up the stock impeller new from the dealer tomorrow, is there a better choice to the stock unit for all around use? This is my first boat with a jet and I have been reading and gaining a lot of very useful information from the threads here so far.

Danosll I hope you get your issue figured out, sounds like you had pretty much the same job on your's as I did. Mine ran well when I got it but the previous owner had destroyed the pump wear ring and impeller on the rocks. It would build rpm but couldn't get out of it's own way.

I think it kinda depends on what you want to use the boat for. Since yours is a single screw then impeller choice is very critical and if you want to pull heavy skiers out of the water going down one step in pitch can make the difference but at the expense of top speed being reduced.

I can't imagine with the stock impeller your boat would experience any difficulty pulling most rafts or innertube types of toys, pulling a skier out of the water is the biggest challenge for my 951 boat, It's more of a struggle and a bit weaker than it should be and so if anything I would go for a bit less pitch if I intended to ski a lot just to get the torque advantage.

I don't normally ski much anymore though, just occasionally, mostly just a 15minute cruise out and hang out then 15 minutes back, so Seadoo's impeller choice seems to be a good overall compromise for my boat.

If your boat was a twin screw, it would be more forgiving and the factory impellers would be able to pull your arms off, so maybe one step larger wheels might be tolerated.

 

[Waterluvr]

Not sure who has what for boats, but generally speaking the SKAT impeller gives both a bit of low end performance as well as top end. Very little as far as whole numbers go but you will feel it in regards to performance. Basically, it will be more responsive.

I'm running a 1997 challenger single 787 Joe, thank you for the input I am going to pick up a stock impeller tomorrow from a dealer and get the boat ready for the weekend but I found a brand new OEM pump housing for sale at a really good price that's ready to go and I would like to try something *better* than stock and mount it on the boat after the holiday weekend.

I thought right away after buying this boat and seeing what the previous owner's encounter with rocks did in a matter of seconds it would be a good idea to have a spare complete pump all built and ready to go for short notice, I will look into those SKAT impellers right now thanks for the suggestion it's very much appreciated.

 

[Waterluvr]

I think it kinda depends on what you want to use the boat for. Since yours is a single screw then impeller choice is very critical and if you want to pull heavy skiers out of the water going down one step in pitch can make the difference but at the expense of top speed being reduced.

I can't imagine with the stock impeller your boat would experience any difficulty pulling most rafts or innertube types of toys, pulling a skier out of the water is the biggest challenge for my 951 boat, It's more of a struggle and a bit weaker than it should be and so if anything I would go for a bit less pitch if I intended to ski a lot just to get the torque advantage.

I don't normally ski much anymore though, just occasionally, mostly just a 15minute cruise out and hang out then 15 minutes back, so Seadoo's impeller choice seems to be a good overall compromise for my boat.

If your boat was a twin screw, it would be more forgiving and the factory impellers would be able to pull your arms off, so maybe one step larger wheels might be tolerated.

I can't ever see us pulling anyone skiing with the boat although we might get one of those tubes for the grandkids. Your point about dropping pitch makes sense for an increased load, same as the prop world essentially. I have zero experience in impeller selection so all this input is really helpful and appreciated guys! I'm looking into the SKAT units right now to see what they offer as Joe recommended.

 

[Sportster-2001-951C-Stock]

I can't ever see us pulling anyone skiing with the boat although we might get one of those tubes for the grandkids. Your point about dropping pitch makes sense for an increased load, same as the prop world essentially. I have zero experience in impeller selection so all this input is really helpful and appreciated guys! I'm looking into the SKAT units right now to see what they offer as Joe recommended.

Yep, even with my stern drive boat I run a smaller wheel around July 4th weekend b/c we often have a fully loaded boat and the larger wheel is a struggle to reach planing speed.

 

[Danosll]

Waterluvr keep me posted on your results . And if you do install an oem impeller maybe you could measure the clearance with a feeler gauge and post the clearances . Like I said before what I find odd is that I have a .020 difference in the center of the blade compared to the tips, on what appears to be an impeccable impeller. There is a complete pump and solas impeller on ebay for under $200. I will try to find link

 

[Danosll]

http://www.ebay.ca/itm/Sea-Doo-787-...raft_Parts&hash=item2ec29d7fdf&vxp=mtr&_uhb=1. This might work I know on solas web sight this is recomended for single 787 challenger

 

[Waterluvr]

Waterluvr keep me posted on your results . And if you do install an oem impeller maybe you could measure the clearance with a feeler gauge and post the clearances . Like I said before what I find odd is that I have a .020 difference in the center of the blade compared to the tips, on what appears to be an impeccable impeller. There is a complete pump and solas impeller on ebay for under $200. I will try to find link

Hey that's a great idea I'm leaving to go see that dealer when they open and I will install that impeller in the housing and take some pictures and measurements for you.

Based on the input Joe gave you regarding clearances from the blade tips to the wear ring I'd say that's likely got to be your issue and in fact having read most everything I could find related to all things affecting jet performance it's the main reason I'm going to just buy a new impeller versus having the old one repaired or going with one of the exchange program units.

I wanted to have everything brand new in that pump to get a baseline on performance for any future issues that come up.

 

[Danosll]

I'm leaning toward aftermarket for a bit more low end. Skat recomends swirl 14.5/22.5 for low end and 17/22 for top.under I can't find a skat distributer. Here in montreal qc. Solas recommends sd-sc-xo.

 

[Waterluvr]

I'm leaning toward aftermarket for a bit more low end. Skat recomends swirl 14.5/22.5 for low end and 17/22 for top.under I can't find a skat distributer. Here in montreal qc. Solas recommends sd-sc-xo.

That's good to know because after looking last night at the Skat's I was unsure as to what to try on my second spare pump unit. My local dealer did not have a stock impeller but he did tell me the stock unit is a 17/22 -5.51 impeller so I'm making the drive to see another out of town dealer to get that this morning.

I'm anxious to see what clearances are when it's all back together, that dealer doesn't open for a few more hours and it's a pretty good drive so at some point this afternoon I'll be back with it and can get that measured up. I went back and read the clearances you posted and that's twice the amount Joe recommended, has to be the source of your troubles.

 

[Danosll]

I agree except I'm within bombardier specs.

 

[Waterluvr]

I agree except I'm within bombardier specs.

What is the factory spec on that? I have only had this boat for a couple days but getting my hands on a proper manual is next on my must have list of things to acquire for it.

 

[Danosll]

here is a copy and paste
Impeller/Wear Ring Clearance
This clearance is critical for jet pump performance.
Clearance can be checked from water inlet opening
or from venturi side. However, the last method
requires more work.
To check clearance from water inlet side, remove
inlet grate.
To check clearance from venturi side, remove
venturi/nozzle assembly as described in Oil Inspection
in this section.
Using a feeler gauge with 30 cm (12 in) blades,
measure clearance between impeller blade tip
and wear ring. Measure each blade at its center.
Clearance should not exceed 1.0 mm (.040 in). If
clearance is greater, disassemble jet pump and inspect
impeller and wear ring. Renew worn parts.

 

[Danosll]

you can join premium membership there should be a manual you can download.
i found an almost new one on kijiji for $30 a couple miles from my home.

 

[Sportster-2001-951C-Stock]

You want that impeller clearance to be as tight as you can get it, so unless are no signs of wear(doubtful) then while the pump is off and especially if the impeller is out of the pump then I'd throw a new wear ring in there. This is why I don't think I'd use a stainless wear ring, the polymer rings can provide a tighter final fit.

I kinda like the Delrin rings b/c they're pretty tough, the impeller can still cut it's way around one of these if it's good and tight, then you can't get any tighter than that assuming your shaft bearings are in good condition and your shaft isn't wobbling around.

 

[Danosll]

New oem wear ring and bearings . I am trying to find a new impeller

 

[Waterluvr]

So I got it all back together, that OEM Impeller is a really snug fit with the OEM wear ring this ought to pump some water max clearance is .007