Re: (ET) Motors (Tim Humphrey)

On 6/13/08, steven1955 comcast net <steven1955 comcast net> wrote:

"I had one go bad last night. Broke a magnet."

Tim,  and others,

I have repaired two permag Elec-trak motors with broken magnets with epoxy, and an expensive Saab convertible top pump motor.  Seeing as the motor shells with broken magnets are normally considered scrap I didn't think there was much to lose by trying.  Bill Gunn wouldn't do this repair, but that may be because, say, a 30% failure rate would have been unacceptable to him and his customers.  To me a 70% success rate at saving motor shells was just fine.  So far my success rate is 100%.

What I used was fresh two part epoxy, and not the 5 minute stuff, purchased from a Home depot kind of store.  5 minute epoxy is not as strong as the regular stuff, and old epoxy does go bad.

Thoroughly degrease the shell and large magnet fragments.  (Just throw out any little magnet chunks.)  I used Berkebile brand solvent based carb cleaner.  If you are more ecologically inclined you could use a strong soap and water, but then rinsing and drying the parts well enough is an issue.  You can have no soap residues left behind, and you may need to bake them in an oven for several hours to really dry them.

Test fit the magnet parts so that you know how you will clamp them.  The magnet parts may push away from where they need to be, so you have to clamp them.  I had several sets of vice grips.  The vice grip jaw can squeeze the shell, but you will need small chunks of wood or plastic to protect the magnet.  The vice grip jaw can fracture the magnet.  (Ask me how I know.)

When you know how you will do the clamping and have all the needed clamps get ready to make a bit of a mess.

You need to add enough epoxy to make sure no air gaps are between the magnet fragments and the shell.  This means that the epoxy will continue to ooze out the edges for some time.  (Don't do this job on your dining room table.)  You may have to wipe off the extra epoxy is it accumulates where something else needs to fit.  As the epoxy oozes the clamps may become loose.  Keep the clamps tight.  I'd recommend leaving the clamps in place for 24 hour after the epoxy hardens

After the epoxy has cured for 24 hours you may remove the clamps.  This is the time to remove any unwanted epoxy.  In particular you must have no epoxy in the ID of the magnets.

Think you're done?  Nope.  I have found that post curing epoxy makes it much harder.  I have a DeLonghi oil filled heater.  I placed the motor shell on top of the heater set on low, and covered the works with a sheet of plastic.  This gets the motor shell too hot to comfortably hold.  Let it sit hot for another 24 hours, then turn off the heat and let it air cool.  You will find the epoxy is much harder than before the post cure.  (This is why you remove any excess epoxy after the first cure.)

If you don't have an oil filled electric heater you can also use an electric kitchen oven on it's lowest setting.  You need to place a cookie sheet or plain old aluminum foil between the motor shell and the heating element.  You don't want the motor radiant heated.  Conduction and convection are just fine.  120 F to 160 F is all you need, and I wouldn't go over 180 F max.  I would not use a gas oven.

Now reassemble your motor.  I have been told that the field strength is weaker when you fix a motor this way, and that makes sense.  However, I cannot tell any difference between the speed of my repaired mower deck motors and the ones with undamaged magnets.  Perhaps my ear based tachometer needs calibration.  My repaired motors have been running for 10+ years now.

Go ahead and try this.  You don't have a whole lot to lose.

Steve Naugler

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