Jet pump hub mod.

[AKnarrowback]

Hi guys!

I might be pulling a "Dr Evil" here and creating something that has existed for the last 30 years. My everyday machine is a 94 XP that I have done a bunch of "custom" things to but have always thought it was really sluggish on the low end with things feeling loaded too heavy. ("Custom" = "you gotta be kidding"). I have already dialed in the carbs, RV cover is machined to spec, all good to go in the running area.

The 140mm pump, with the larger center hub, and the swirl type impellers got me thinking. I'm not sure if there is a larger hub pump that bolts to the original pattern hull (88-94ish). Since the budget is always a goose egg I went McGiver on my pump, had a sleeve 3d printed by a friend and grabbed the JB Weld. The sleeve ID matched the old pump, OD matched a large hub, I cut 6 pieces to match the pump veins, got creative with damming the ends and went to town with the glue. After things cured I spent an hour with the dremmel and a variety of bits to smooth things. It's not perfect, I have a bunch of clean up to do, but the test ride was pretty eye opening.

The only impeller I had was an 11/22 out of a 99 GTI, it needed a bunch of tlc, but it was a lucky shot in the dark. The low and mid range responsiveness is significantly better, top rpms are around 6900, I did not have the GPS but I would guess it is the same or a hair slower.

WooHoo! Sometimes I amaze myself.

Time to pull it apart, mix up more JB to clean up/fine tune the surfaces.

 

[etemplet]

Man I'm sitting here laughing my azz off. Macgyver ain't got shiznit on you. I can't believe you're not having cavitation issues and the impeller... what a stroke of good fortune!! Looks like it's SPOT ON !!

What engine is in that ski right now?

 

[AKnarrowback]

Took it out for a second ride because I found my GPS. Dropped top speed by 3ish mph,

An old Friend had a couple of aluminum pumps, one with some vein damage, so I had my chance to try the idea. He had given me a couple of used impellers, only one was for a 140mm big hub pump so I'm feeling lucky it is pitched to give me a strong hit down low and puts top end rpms in a good area,

I'll be the first one to admit it's ugly, but I had to know if it would work. As it is I have two pumps, one for more speed, one for playing and I can swap them out in 10 minutes to match the day.

 

[AKnarrowback]

Man I'm sitting here laughing my azz off. Macgyver ain't got shiznit on you. I can't believe you're not having cavitation issues and the impeller... what a stroke of good fortune!! Looks like it's SPOT ON !!

What engine is in that ski right now?

It's my stock 94xp with the 657x.

 

[AKnarrowback]

And I took things apart after the test ride.

One of the epoxy fillers did blow out the back so the other 5 are bound to jump ship as well.

All the remaining fillers had some evidence of thin epoxy areas breaking off of the plastic core I used.

The bearings are nice and clean, with the one filler gone the pump blast found it's way in and completely emptied the oil out.

I'm not beat yet. The performance difference was enough for me to want to find a way to make this work. Not sure how right now, I'm thinking removing the fillers and sand casting metal inserts I can bolt in. I have no idea how to sand cast or melt aluminum, but that's just part of the process.

 

[etemplet]

Is it the bolt pattern that won't line up on the pump or the gasket sealing surface?

 

[AKnarrowback]

Gasket surface in the cone. The larger cone and the small hub pump do not have any way for an o-ring to be used. I slapped it together with some right stuff knowing I only had a short time on the water before something might fail. I did a ten minute test, got the info I needed and now I'm back to the drawing board. The hole pattern for the big cone and small hub matches. I'll have to figure out a way to seal things.

 

[etemplet]

So you need to machine a surface on the inside of the cone (a counterbore) then machine a bushing to press into the cone to give you the surface you need. The bushing can be machined complete then pressed into the counterbore on the cone and VIOLA... you're done. It would take some finess' to get that done though but it is doable.