98 sportster cavitation

[LawnDart]

Hi everyone. I bought a 98 sportster 1800 which is in pretty good shape other than some pump issues. Both pumps cavitate when coming out of the hole, even with just me in the boat. If you throttle up each engine individually the boat doesn't even move......just spins up to seven grand.

The pumps visually look good and the previous owner said he had new wear rings and impellers fitted. So how much cavitation is normal on these boats? What should I check first.......the impeller clearance? Are there aftermarket parts like scoop grates for these boats?

 

[Coastiejoe]

On a boat, some cavitation is normal due to the load of the boat. But no where near what you describe. I would personally look at the wear rings. The gap should be thinner than the width of a dime. If the impelled are right, not bent, and the wear rings are good, then look at the carbon seals next. I would do the wire tie trick to see if it improves. If so, then replace the carbon seals.

Do you get water in the hull?


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[LawnDart]

As best I can tell with a flashlight inspection the wear rings look good, and the impeller edges look fine. The leading edges look like a new grind so the impellers may be remans?? I'll put a feeler gauge in there tonight but it looked tighter than dime thickness.

There was some water in the hull.......no a lot though. Also one of the shafts had some blue plastic exposed on the water side where it feeds through the hull. What could this be?

Thanks a bunch. I really appreciate the help.

 

[Coastiejoe]

The blue plastic is a sleeve that is suppose to help protect the shaft and make it easier for you to remove things that get wrapped up on the shaft. Once it starts to break up, break the rest off, it is not needed for the boat. Will cause no issues without it.


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[LawnDart]

Will do, thanks.

 

[Waterluvr]

Your pumps were intended to be siliconed to the face of the pump support. Pull them, clean it all up good and make sure you're using the OEM wear ring with the right lip on it and use black rtv on the face edge of the wear ring and the support it will seal right up nicely.

Those will draw air installed any other way or with an aftermarket wear ring.

 

[LawnDart]

For the most part I could only get a .024 feeler gauge in the pumps, on one location I got a .028in to go. Is that too much clearance? I trimmed the blue insert back as best I could with a utility knife. The picture below is the rougher of the two impellers. The other one doesn't have any dings.

I did the "grease gun trick" I found in another post and I could get the whole carbon ring/stainless flange to move back and forth. Does this mean they are bad? There was very little pressure from the boot, I could move the carbon ring back with a couple fingers.

 

[LawnDart]

How hard is it to pull the pumps?

 

[Coastiejoe]

As a general rule, anything ver ten-thousands of an inch is too much. The bigger the gap the worse it is, especially on a boat due to the load.

 

[LawnDart]

New wear rings or can you shim them?

 

[2UCS]

Sweet Boat LawnDart I just picked one up last Friday to love it

 

[Isaac-1]

It is fairly easy to pull the pumps if you don't have salltwater corrosion to deal with. I just bought my 99 Sportster 1800 less than 2 weeks ago, and have already had to pull the pumps twice, and will need to do one again in a few days when more parts get in. First time through I would say plan on it taking 30-45 minutes to pull taking your tme and going slow, and probably about the same maybe a little less going back on using just hand tools. The second time around I pulled everything off, fixed the minor issue with one pump and put it back together in about an hour.

 

[LawnDart]

OK so I fitted new wear rings and sealed everything up. One pump has near zero impeller/wear ring clearance. The other pump housing is slightly out of round. It is zero clearance on the top side and .011 on the bottom. The shaft is straight.

So the question is what are my options for pump housings? Are there aftermarket housings available?

I also moved the stainless flange/carbon seal one clip back on the driveshaft for a little more preload on the seal.

Thanks for the help everyone.

 

[LawnDart]

That did the trick. Almost no cavitation now the boat jumps on plane.

Here is a tip..........I was struggling to push the carbon seals back to the next clip until I got a pair of channel locks. Twist (lightly, don't bend) the stainless flange while pushing and they slide back nice and easy.

 

[Isaac-1]

When you say twist do you mean like you would twist to unscrew it if it were threaded on, or twist like popping the top of a pop top bottle?

 

[LawnDart]

I lightly grabbed the cylindrical portion of the stainless part with channel locks then just wiggled it back and fourth while I pushed on flange portion..........if that makes sense. It went back super easy compared to the 30 minutes I spent pushing on the flange alone before that. I loosened both the boot clamps and re-tightened to make sure everything was lined up.

edit-I also made sure the stainless flange was re-seated against the clip......wiggled it back and fourth while pushing forward to the clip.