Little Giant Pump (instructional)

[logiktest]

I thought this might be interesting for those of you who own Little Giant pumps. My return pump stopped working one day while performing a water change, and not wanting to buy a new pump, I decided to disassemble and diagnose the problem myself, and see if I could save a few bucks. I have not seen any DIY tutorials on this procedure, so I thought I would share my experience rebuilding this pump with you.

This pump, specifically, is a Little Giant 3-MDQX-SC. I would imagine that other models of Little Giant pumps are very similar. And, seeing as this article is instructional, I will not be held liable for any misjudgment or stupidity on your part. This pump is an electrical component, and an inherently dangerous project. Stay safe, and if your incapable of performing the procedure, don't.


Tools used:

Very Large Flat Head Screwdriver
#2 Phillips Head Screwdriver
5/16" Socket or Wrench
11/32" Socket or Wrench
3/32" Allen Wrench
Channel Lock Pliers
Bearing Puller or Pulley Puller
Hammer
Small Nail Setter

Materials used:

3-in-1 Oil
Four Cotton Balls


Step One, Begin by removing the four nuts on the impeller housing cover with a 5/16" socket and removing the impeller housing cover. Then remove the impeller by hand.

Step Two, Use the channel lock pliers to unthread and removed the bolts that extend through the impeller housing cover, making sure not to grasp the threaded portion of the bolt. After the four bolts are removed, the impeller housing slides right off, revealing the magnetic pulley.

Step Three, Use the 3/32" Allen wrench to remove the set screw that holds the magnetic pulley to the motors shaft. There is a recess on the plastic ring between the pulley and the motor housing to fit the Allen wrench, simply align the recess with the set screw to remove. Take note of the distance between the magnetic pulley and the plastic ring. You will want to use this same distance upon reassembly.

Step Four, Remove the magnetic pulley using a pulley puller. A very large flat head screwdriver would also be an option, slowly working around the pulley and prying it off bit by bit.

And some more pictures better illustrating the rings recess (at 3 o'clock in pic) and the set screw location on the pulley:

 

[logiktest]

Step Five, Using the #2 Phillips head screwdriver, remove the four Phillips screws that hold the plastic ring to the motor cover. Remove the two plastic oil plugs from the motor housing now.

Step Six, Now, turning to the opposite side of the pump, use the 5/16" socket again to remove the two acorn nuts that hold the wiring cover to the motor housing. Then slide the the cover off the bolts, but don't try to completely remove the cover yet.

Step Seven, The wires need to be disconnected from the relay inside the cover. The wires have spade connectors and are easily disconnected/connected by hand. Keep note of exactly where the wires are connected, you'll need to know this for reassembly. Once the wires are disconnected, the relay may be removed from the motor housing cap using the 11/32" socket or wrench. The wiring cover may be completely removed now. The bolts in the motor housing cap will not be removed because they are welded to the underside of the cap.

Step Eight, Now the fun part. The motor housing has four clips that hold the housing cap in place. These will need to be removed. Using a small nail setter or small flat blade screwdriver place the tool between the clip and the motor housing and cap. Gently hit with a hammer until the clip comes free. Be very careful with this step, when I removed the first clip, it shot across the room about twenty feet at an incredible velocity. Eye protection would serve you well during this step.

You may now remove the cap. The cap will have to hang from the housing due to the wires for the remainder of the project. Notice the rings on the underside of the cap which I will refer to as a bearing from here on out. Inspect the underside of the cap and rear bearing for any odd scoring or burn marks.

Step Nine, Let's take a look inside the pump. We find an armature with washers, and a coil.

Pulling the armature out of the coil will reveal the inside of the coil and the front bearing. Take note of the orientation of all washers before removal of the armature. There are washers at both ends of the armature. You can now see how oil reaches the front bearing via the tube in he motor housing similar to the rear bearing in the housing cap. Inspect the Armature, coil, and front bearing for scoring or burns.

 

[logiktest]

The armature:

Step Ten, Now that the pump is completely disassembled, the front and rear bearing material should be replaced. To remove the material, use the 3/32" Allen wrench or a similar device to pick and scrape out the old material.

This is where the 3-in-1 Oil and cotton balls come into play. Steal at least four of them from your wife, girlfriend, mother, grandmother, or take one cotton ball from each of them so that no one is the wiser. This will be the material used to repack the front and rear bearings.

To repack the bearings, take one cotton ball, lubricate with a few drops of oil, and squish it between your fingers to form a pancake shape. Next impale the pancake shape on the center of its face using the 3/32" Allen wrench to form a hole. Enlarge the hole with your fingers until the cotton ball resembles the shape of a doughnut. the doughnut can now be packed inside the bearing. The 3/32" Allen wrench will help. Repeat this with the other three cotton balls until both front and rear bearings are repacked.

 

[logiktest]

A few notes:

Note 1, I lubricated the armature shaft where it meets the bearings with lithium grease before reinstalling. I also lubricated between the washers.

Note 2, When reinstalling clips on the motor housing and cap, insert the clips in the housing first, then once struck (gently) with the hammer, the clips will correctly snap into the cap.

Note 3, Briefly test pump dry before installing.

Note 4, Don't forget to refill the pump with oil before restarting.

Note 5, Do not over tighten the bolts that connect to the impeller housing or any of the nuts.

Assembly is the reverse of disassembly.

Your done:

Clean up, kick back, and admire your handiwork.

 

[customcolor]

so what was wrong with the pump?

 

[kcress]

Great How To! Thanks.

 

[logiktest]

Hello Costomcolor, Not wanting to speculate too much, I'd guess that the magnetic pulley(as I labeled it) Was out of adjustment, due to the high quality of the armature and coil upon my tear-down inspection. It is very possible that the "Pulley" came loose, or slowly re adjusted over time due to the set-screw working out of adjustment gradually. If this was the case, Step three Would be the appropriate time to check for this scenario by plugging the pump back in, and checking clearances between the pulley and the impeller housing for fitment.

PS. Your foam reef (arch) has always been an inspiration to us all (I built one too!), yet your signature un-savors the point due to it's length(scrolling and scrolling, man!). No offense, your work is top notch by any standard.

Hello Kcress, Thank you kindly!

 

[kcress]

What I want to know and I didn't see here is how you dealt with the absolute POS fan they have on the non-drive-end.

I have mine apart and want to wire brush off the fan and repaint the corroded mess, but it's one of those crimped on junk fans. It has no hub even. If I take it off I fear it will never grab the shaft again.

 

[Gary Majchrzak]

good thread

good thread

one thing many people don't realize is the fact that these LG pumps require regular oiling.

Place oil (I use the 3 in 1 brand) into the hole capped with a yellow plug in this picture. Some LG pumps have two holes to place oil.

(may I borrow this picture for future references?)

I use 3 in 1 brand SAE 20

 

[Jyetman]

A few notes:

Note 1, I lubricated the armature shaft where it meets the bearings with lithium grease before reinstalling. I also lubricated between the washers.

Note 2, When reinstalling clips on the motor housing and cap, insert the clips in the housing first, then once struck (gently) with the hammer, the clips will correctly snap into the cap.

Note 3, Briefly test pump dry before installing.

Note 4, Don't forget to refill the pump with oil before restarting.

Note 5, Do not over tighten the bolts that connect to the impeller housing or any of the nuts.

Assembly is the reverse of disassembly.

Your done:

Clean up, kick back, and admire your handiwork.

I know this is five years old but how many drops of oil is considered refilling?

 

[uncleof6]

I know this is five years old but how many drops of oil is considered refilling?

Line 1 of the service instructions reads:

"The motor's sleeve bearings should be lubricated every six month's with two to three drops of S.A.E. 20 weight non-detergent oil. The oil holes are located on top at each end of the motor."

Before that, up at the very top, the instructions read:

"RETAIN THESE INSTRUCTIONS FOR FUTURE REFERENCE."

To that end, here are the instructions:

http://www.plumbersurplus.com/pdf/08023.pdf

If the pump had been oiled regularly, the pump would most likely not have required any repairs. I have a 30 something year old pump that has been maintained, and the only repairs to it have been to replace the volute and impeller, and replacing the cord.

There are no internal parts of the motors, aside from the volute, impeller, ceramic shaft, etc. that should be serviced by the end user. That being the case, there is no official information published on how you should proceed now, to ensure the pump does not fail next week, or the week after. At the top of the instructions is the phone number with which you can reach Franklin Electric. It is my suggestion that you call them and ask them.