Merc sport jet 120xr cavitating?

[Gates312]

I have a 97 sugar sand mirage with the sport jet 120xr. It runs awesome but tends to take bit to plane out and will only run about 34mph. Looking at the pump today i noticed the foam seal between the hull and the stator seems to have popped out on the port side. The starboard side looks like it is still set in well. Could this cause a cavitation issue? Wear ring and impeller both look good as well as ride plate gasket. Photos attached, thanks

 

[tdonoughue]

Disclaimer: Don't really know anything about that particular boat or jet.

But my advice would be to pull the pump and check it (unless you can get a good view of that gasket from aft or below). If the gasket has shifted, part could be in the water path and could impact performance (either directly by blocking the flow some or by introducing cavitation, which then can also ruin your impeller if too bad). Not sure how bad the pump pull process is on the Sugar Sands (but on the Yammies it is pretty easy--just back from pulling mine just to inspect), but that would be my first step. Of course, if you find an issue, you can then correct it with the pump off.

 

[Gates312]

Disclaimer: Don't really know anything about that particular boat or jet.

But my advice would be to pull the pump and check it (unless you can get a good view of that gasket from aft or below). If the gasket has shifted, part could be in the water path and could impact performance (either directly by blocking the flow some or by introducing cavitation, which then can also ruin your impeller if too bad). Not sure how bad the pump pull process is on the Sugar Sands (but on the Yammies it is pretty easy--just back from pulling mine just to inspect), but that would be my first step. Of course, if you find an issue, you can then correct it with the pump off.

Im gonna pull the pump and get a better look at the wear ring and impellor. Ill look at that foam gasket while im in there. Thanks

 

[tdonoughue]

Good deal. Take plenty of pics for us.

 

[Gates312]

Good deal. Take plenty of pics for us.

Pump pull process was very easy. 10 minutes and i had it out. What was weird to me was none of the seams were sealed between the pump sections. Each section has flanges so they all seam up perfectly, but this to me seems very un-natural to not have any sealant between the sections, maybe someone has been into this pump before me. Have you ever seen this?
The wear ring has some minor grooves and pitting, tolerances were a little high, gonna try the jb weld fix for now.
Impeller appears to be in awesome shape to me, have yet to pull it from the shaft.
Last thing, the stator veins look ok but seem a little rounded on the ends. And what is the circular saw blade looking deal inside of the stator housing? Something for oil flow for the end of the shaft where it rides in the housing?
Id appreciate it if you could let me know your thoughts on sealing the seams, my impeller, and the stator veins. Thanks

 

[tdonoughue]

Good pics!

So, first, on sealing the seams: I advise no. My sections (mind you, on a Yammy) are not sealed. And if you seal them, that 10 min job to pull the pump will be much, much longer.

Impeller: Your leading edge looks good, but I am seeing some cavitation rash (near the center, back from the leading edge--that, well, rash looking stuff. During cavitation, micro bubbles are created at the leading edge. They travel along the impeller and as the pressure decreases, they pop leaving a rash. That is one of the key indicators of cavitation damage. Of course, then that roughens the surface, creating things that are more ripe for cavitation...

Wear ring: Of course, it should be smooth. The fact that it has grooves and pitting indicates that it likely has swelled and is impacting the impeller. That's bad, of course. That means you should be replacing the wear ring. Next thing you need to know is the tolerance spec for between the ring and the impeller. It should be close, but not too close (like touching). One of those things that you have to measure with a wire gauge or similar (same as with a spark plug). JB Weld likely will not work, as that will build up the material and put you back in contact with the impeller. Sorry.

Now, the veins and the saw blade thingy: No idea on the saw thingy! Usually under that part you have a bearing, so that saw part is probably removeable, I would guess, so you can get to (and inspect or replace) the bearing. Probably someone who has worked on a Sugar Sand can help there...