Mines set at 20 thousands


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What clearance are you at now?

The diameter should have .025 and the front clearance, we set it at .035 to .055 depending on the application.  As the clearance opens up, efficiency is lost.  You will feel that most in the launch as the pump will not build pressure as fast.

I heard something a while back about someone doing a test where a jet boat was tied to a dock under full throttle with and without a wear ring installed.  Supposedly, full thrust was achieved in both tests, however the rate at which thrust was made was much slower without the wear ring.  I don't think, with that much internal leakage, the same thrust could be achieved.

There is more to it than all that.

If your impeller has labyrinth grooves, you can run them up to about .030" without any real ill effects. This is how a typical river pump is built for commercial service to allow sand to pass without any real wear concerns.

Something else to consider is how snug the bowl bearings fit the tail shaft, if the tail shaft is allowed to flail, the impeller clearance becomes irrelevant.

I am a .012" per side, square dude. .

On a stainless, no less than  .015" total. Aluminum, I won't go tighter than
020"

If you can slip a .028" feeler into the "front" of the wear ring to impeller, you need a do over. Obviously the impeller and wear ring need to be in your hand.

Ultimate wear ring, all bets and standards are different.

GT

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Thank you gentlemen, that puts me in the right direction. Putting a pump together from bits and pieces. I did a dry fit and feeler gauge .045" total. I guess she's a little more blown out than I thought.


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No, I believe it's stainless.


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It is really difficult to measure clearance on the diameter that way.  Really, the best you can do through the hand hole is front clearance.  My guess is that if you are trying to bend feeler gauges around the 90-degree bend created at the front of the wear ring surfaces, you have way more clearance than you think.

For the diameter, you really need to measure with the impeller and shaft removed.  Because of the flange and register on the suction housing, you can't really get in to measure with calipers.  A dial bore gauge or inside micrometer works best.  If you want to pursue the feeler gauge approach, you could try, after removing the shaft, wrapping feeler gauges around the wear ring surface of the impeller and fitting it to the wear ring.

I'm assuming budget is prohibiting the purchase of a new wear ring and liner.  Can you see shims installed on the shaft in front of the impeller hub?  If so, you could tighten up the front clearance.  This is the clearance between the front of the lip of the wear ring surface of the impeller and the suction housing.  If you have a bronze shouldered wear ring, this clearance will be between the impeller and the shoulder of the wear ring rather than the suction housing surface.

Depending on how and where you boat, we set that front clearance accordingly.  If you prefer to drive on/off the beach or you primarily boat on the river or basically anywhere where you will pick up abrasives, you will want to give it a little more clearance.  If you boat in cleaner water, tighten it up for performance.

We typically set the innitial front clearance at .035 for a performance application.  This also brings in the clearance at the back of the wear ring at the same time.  We believe that it is the bending of the water around these 90-degree edges that prevents the most internal leakage.  One grain of sand can lock up a pump with tight clearance.  In that case, you could push it as close as .055.  Factory clearance of 1/8 inch is too much.  Be warned that if you don't have shims currently installed, the shaft will need to be machined.

Honestly, if everything is sound but clearances are just a little loose, I would leave it alone until budget permits a new wear ring.  It will be a little slushy out of the hole and be down a few MPH, but since it's not a race deal...

Good luck,

Joe

P.S.  clearance is just one aspect of pump performance.  You really need to look at the big picture.

Sorry Joe, I should have explained a little better. The shaft is out of the pump. The only thing installed on the pump housing is the wear ring. I was using a set of 45 degree feeler gauges (only because I can't remember who I let borrow my bore gauge). I'll take home my set of calipers from work and get a better reading tonight.

I don't mind getting a new wear ring, just wanted a better understanding before I go ordering parts. I will be running at the river and probably hitting sand bars once in a awhile so a looser set up is probably what I'll need.

Thanks for all the input!!
Tim


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To do it that way, I use dual feeler gauges. They don't need to be the same size really, you need to do the math.

GT

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