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Topic: HWP motor problem and solution (2 msgs / 107 lines)
1) From: Charles K. LEE
This is a multi-part message in MIME format.
Tom: If you are still using the Hearthwares as sample roasters, you may =
find the following of some use.
After my second HWP died at 296 roasts I ordered a new motor and =
examined the failure mode.  The motor is a good one but it is designed =
to be used horizontally.  It has a stainless steel shaft running on =
robust self-centering oilite bronze bearings but no real thrust =
bearings.  At the brush-commutator  end of the motor shaft there are, =
between the end of the commutator  and the shaft bearing mount, a thin =
nylon or teflon antifriction washer and a phenolic washer.  The fan end =
is similar but with a wave washer added as a spring to lightly preload =
the rotor and commutator against the brush end of the motor.  If the =
motor were used horizontally it should have a lifetime of several =
thousand hours, depending on load.  However, when it is mounted =
vertically the weight of the rotor, commutator and fan puts an unfair =
load on the bottom end of the motor.  The little antifriction washer and =
the phenolic washer get chewed up by the bottom bearing mount.  As the =
bottom bearing mount grinds into the end of the commutator everything =
drops down until the fan hits the fan shroud with the dreaded scream of =
death.  The two HWPs I have failed at 30 hours (replaced under warranty) =
and 50 hours (replaced the motor - $15.00 + shipping).
To fix the problem you need to add a thrust bearing.  A way to do this =
is to buy two brass #8 washers at your local hardware store - mine cost =
6 cents each.  You want brass because brass and steel when lubed make an =
acceptable bearing.  The washers dimensions should be 0.176 inches ID, =
0.375 inches OD and 0.032 inches thick, which seems to be the standard.  =
There are oilite thrust washers and thrust bearings but they are much =
more expensive and have long lead times.  I have ordered some because =
the oilite would eliminate periodic oiling.
Unplug the unit from AC power and remove the roast chamber assembly.  =
Place the HWP base upside down on some newspaper and remove the 3 bottom =
screws.  A 6 inch #2 phillips screwdriver is useful here because the =
screws are in deep wells.  Lift off the cover and you will see the motor =
attached to a black plastic shroud that is the bottom of the fan =
housing.  The shroud is attached to the heat chamber with 3 bigger =
screws (the same size as the bottom screws) and at least 3 smaller =
screws (there may be more on some units).  Remove these and unplug the =
motor from the control board.  If the wires are bundled with a cable =
tie, remove it.  Lift the motor and shroud from the heater assembly and =
examine it.  Notice the endplay; push and pull on the fan disk - this =
movement is what you need to control.  If the endplay is 1/16 inch or =
more you will need both washers.  Unscrew the fan disk; you may need to =
hold the end of the shaft with pliers.  Remove the two screws with =
washers that fasten the motor to the fan shroud and separate the shroud =
from the motor.  At the threaded end of the motor is an c-ring.  Remove =
it.  (Small needle nose pliers will work).  Save all the pieces.  
Now you are going to make a thrust bearing by pressing the brass washers =
onto the motor shaft.. You will need a tool to press the washers - I =
used a 3/16 inch nutdriver but a 3/16 inch 1/4 drive socket would work =
or perhaps a replaceable tip screwdriver.  What you want is a tool that =
will engage the washer but is hollow inside to clear the motor shaft.  =
Examine your washers, (they are stamped from sheet brass) and one side =
will be slightly rounded.  Hold your motor vertical with the threaded =
end up and the other against something solid.  Place the washer, rounded =
side down, on the shaft and press it down to the bearing mount.  If your =
motor had enough endplay to be noisy, you will need to add the second =
washer.  Replace the c-ring and tap on the threaded end of the motor =
shaft to seat the washers tightly against the c-ring.  Lube your new =
thrust bearing with a good oil, such as electric motor oil; I used a =
synthetic base gun oil.  The motor should now spin freely.
On the motor armature the letter P is stamped.  Fasten the motor back on =
the shroud with the P side facing towards the two posts on the shroud, =
using the two screws and washers.  Spin the fan back on the threaded =
shaft.  Notice the flat side on the shroud: it lines up with the flat =
side of the heater assembly.  Attach the motor shroud assembly back on =
the heater assembly with the 3 bigger screws and the 3 or more smaller =
screws.  Plug the motor connector back on the control board and bundle =
the wires with a cable tie.  Put the control panel back in its slot on =
the black plastic ring.  Slide the base back on and fasten its 3 screws. =
 Turn the base over, add the roast chamber, plug in the AC power and =
test.  I've modified two HWPs - both work fine - but each has only two =
hours use so far.  They will probably require oiling every 10 hours.
I called Hearthware Service to tell them of the problem and its =
solution.  They said they will look into it.  Hearthware Service should =
be commended for doing a good job in supporting these units.  It is =
regrettable that their management didn't have an engineer do a failure =
analysis.
Respectfully, Chuck

2) From: Ben Treichel
Chuck,
Good analysis.
Charles K. LEE wrote:
<Snip>
I know an engineer that looked at their problem with boards burning out, 
but they didn't want to pay for engineering to solve that issue either.
It makes me worry that their new roaster will have all of the desirable 
features, and shoddy engineering; and that the first adapters will be 
'beta guinea pigs' just like Microsoft does with their o/s releases 
(minus the desirable features in MS's case).
<Snip>
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