Impeller modifications.

[xXx Octane xXx]

After test fitting three different 148mm impellers in a Maxxx 148mm pump last week, I found the trailing edges of the blades on all three of my impellers to sit 7mm to 8mm+ away from the leading edges of the pump stator vanes.
I made a tool out of a "couch" driveshaft to hold the impellers in a lathe chuck. The flats on the largest diameter are to put a wrench on or to put in a vise when installing or removing the impellers.
Prior to modification, the distance from the part of impeller that seats against the driveshaft to the back of the hub was between 18mm and 19mm on all three impellers. I increased this distance on all three impellers to ~26mm on a lathe and recessed the three ribs an additional ~1mm on a mill.
The hubs of all three impellers are about as close as they can get without making contact with the hub of the pump right now and the trailing edges of the blades are also almost in contact with the leading edges of the stator vanes of the pump. I plan to add a 0.5mm shim prior to final assembly.
Is there anything that I may have overlooked that I need to be aware of?

 

[SuperDrifter]

not an engineer... but blade flex under load affecting tolerances?

 

[OCD Solutions]

You can do all that and you are asking us for advice? Me thinks we are the ones that should be asking you such questions...

Sounds like you did a damn fine job to me and if you do find it binds under load, you can just add a shim or two til it clears. Normal setback is -3 to -5mm but I've seen -7 and -9 before by special request.

 

[xXx Octane xXx]

Thanks for the feedback!

All three of these impellers are "standard blade" Skat-trak so I'm hoping they won't flex too much under load.

I know that in theory the "thin blade" modification that Skat-Trak offers allows the leading edge pitch to flex higher and the trailing edge pitch to flex lower but I don't know how much movement there actually is under load.

Based off of the measurements taken on three different 144mm Impros "Hookers" (which are said to be -7mm cut back), these three 148mm impellers are now around -12.5mm cutback.

 

[DAG]

A call to Skat may save you some future headache's

 

[TheBuzzard]

with zero clearance between the blades and pump veins, you better hope you dont suck nothing thru the pump.

 

[xXx Octane xXx]

A call to Skat may save you some future headache's

From past experience, having Skat-Trak modify parts to work with a pump they don't make has not turned out well for me.

The impeller fitment issues are fairly easy to correct with the right tools and some time. Overall the Maxxx pump is a very nice part. The galvanic couple (which will likely cause issues at some point, especially in salt water) found between the stainless wear ring and aluminum pump housing on Skat-Trak pumps does not exist on the Maxxx pumps in this area. The Maxxx pumps utilize an aluminum insert for the bearings in the hub of the pump just like the Skat pumps (the aluminum has more compliance for the press fit of the bearings than a stainless steel hub like that of the Solas pump). The Maxxx driveshaft is not quite up to par with an OEM driveshaft (different material and lower hardness: Maxxx 26.0 - 27.0 HRC vs. OEM 41.5 - 42.5 HRC), but no aftermarket driveshaft that I have seen is as good as the OEM driveshaft.
I do hope that Maxxx considers making a two piece (separate wear ring and pump housing) version of his pump in the future. (They are a lot easier to work on).

 

[tomski]

A call to Skat may save you some future headache's

Hello Skat Trak (Glen), I'd like to tell you the impellers you make don't fit the 148mm maxx pump correctly...

 

[LegDragger64]

I had to do additional cut back on the props for 144 Maxx pump. Seems like it was an extra 4mm vs skat mag cutback . Even the cutback on a skat mag is different from a stock pump.
If it gets to close all you need is a shim or two.

 

[DAG]

All three of these impellers are "standard blade" Skat-trak so I'm hoping they won't flex too much under load.

A call to Skat may save you some future headache's

Skat should be able to tell you how much flex there props have and how much clearance to give,

@tomski why would skat need to know what pump its in; nice try at trying to make me look like a dumbass. noted

 

[OCD Solutions]

Would it be possible to machine the Maxx pump instead of each individual impeller? Seems more logical in the long run if there is enough material to allow it.

 

[LegDragger64]

You could machine the step on driveshaft so the prop goes on further . That means breaking down pump and new bearings , i run ceramic bearings and there not cheap Machining pump would not help. Would make gap bigger. Before the cut back , there was an excessive gap between rim of prop and stator hub .

 

[tomski]

@tomski why would skat need to know what pump its in; nice try at trying to make me look like a dumbass. noted

Should I try again?

 

[kevbo]

After test fitting three different 148mm impellers in a Maxxx 148mm pump last week, I found the trailing edges of the blades on all three of my impellers to sit 7mm to 8mm+ away from the leading edges of the pump stator vanes.
I made a tool out of a "couch" driveshaft to hold the impellers in a lathe chuck. The flats on the largest diameter are to put a wrench on or to put in a vise when installing or removing the impellers.
Prior to modification, the distance from the part of impeller that seats against the driveshaft to the back of the hub was between 18mm and 19mm on all three impellers. I increased this distance on all three impellers to ~26mm on a lathe and recessed the three ribs an additional ~1mm on a mill.
The hubs of all three impellers are about as close as they can get without making contact with the hub of the pump right now and the trailing edges of the blades are also almost in contact with the leading edges of the stator vanes of the pump. I plan to add a 0.5mm shim prior to final assembly.
Is there anything that I may have overlooked that I need to be aware of?

View attachment 241067 View attachment 241068 View attachment 241069

I think it is a waste of time as a performance mod. Shops push any mod that they can cash in on. I have made a similar tool for adapting Kawasaki 750 impellers to 650 pumps. All that matters is that the impeller is held straight.

 

[DirtKurt]

Thats pretty funny that you made this thread, we were measuring the exact same thing last week Re-building a maxx 148 and maxx 150. Came to the same conclusion with the setback and were planning on sending the impellers to impros to get cutback

 

[keith t]

You can run a double race bearing that is 3mm wider than a single race, this effectively moves the shaft back and therefore the back edge of impeller is closer to the pump static veins.

 

[xXx Octane xXx]

I think it is a waste of time as a performance mod. Shops push any mod that they can cash in on. I have made a similar tool for adapting Kawasaki 750 impellers to 650 pumps. All that matters is that the impeller is held straight.

This modification is not necessarily intended as a performance modification. Instead it provides another tuning variable. Impeller pitch, impeller placement, reduction nozzle diameter, and pump cone sizes all have an affect on the performance of the pump.

Moving the impeller closer to the stator vanes of the pump has a similar affect to increasing the pitch of the impeller, reducing the reduction nozzle size, or using a longer pump cone.

Moving the impeller further away from the stator vanes of the pump has a similar affect to decreasing the pitch of the impeller, increasing the reduction nozzle size, or using a shorter pump cone.

 

[Philip Clemmons]

This modification is not necessarily intended as a performance modification. Instead it provides another tuning variable. Impeller pitch, impeller placement, reduction nozzle diameter, and pump cone sizes all have an affect on the performance of the pump.

Moving the impeller closer to the stator vanes of the pump has a similar affect to increasing the pitch of the impeller, reducing the reduction nozzle size, or using a longer pump cone.

Moving the impeller further away from the stator vanes of the pump has a similar affect to decreasing the pitch of the impeller, increasing the reduction nozzle size, or using a shorter pump cone.

I've heard that before

 

[LegDragger64]

You can run a double race bearing that is 3mm wider than a single race, this effectively moves the shaft back and therefore the back edge of impeller is closer to the pump static veins.

Rear bearing is already up against flange of tailcone . No room to move it back .

Pump uses a 5205 double row in front 20.6mm wide. 6205 in back 15mm wide

3mm wouldn't be enough. Had to cut back 8mm total.

 

[xXx Octane xXx]

It looks like around 3mm could be machined off of the step of the driveshaft behind the threads and in front of the first oil seal if you wanted to go that route.