Midwest Shorty User manual

Midwest Shorty 2-Speed Motor
The Midwest Shorty 2-speed motor has been in existence for many years. It is a durable
handpiece and has a speed range of 0 – 30000 rpm. It has replaced the Midwest Tru-Torc
and you will come across them quite often in the field. Many aftermarket replacement
parts exist for this handpiece. As always, try to determine the problem before
disassembling the handpiece.
Some of the most common problems and solutions are addressed in the Midwest Tru-
Torc and Shorty troubleshooting guide immediately preceding this section.
Sub Assembly A & B Disassembly
STEP 1
Remove the front sheath housing. Do this by
placing it in a 3/4”collet just below the spindle
lock button as shown. Then wrap a strip of
rubber around the speed change collar and
motor housing and unscrew. All the threads on this handpiece are
regular thread, so turn counterclockwise to remove. Next, simply
unscrew the speed change collar screws and remove the collar.
STEP 2
Lock the clutch housing of the handpiece into a 49/64” collet. Loosen
the upper turbine housing by hand and remove. Remove any spacer
washer(s) and place them on your work surface.
Sub Assembly A Disassembly (Nose Section)
STEP 3
Line the wide drive rings up with the half moon grooves in the
clutch as shown at left. Reach under the drive plate with a flat thin
screwdriver. Pry the plate up. This will expose the three wide
drive rings. Place them along side the drive plate on your work
surface. You may need to work your way around slowly while
always prying UP on the drive plate.

STEP 4
Now that the drive plate and wide drive rings have been removed, place
a 3/16” collet into the collet holder. Insert the spindle halfway above
the fork, into the collet. Once the collet is tightened, use a flat head
screwdriver to unscrew the spindle bolt. Then pull the various pieces
apart and place on your work surface.
STEP 5
You can now place the nosepiece in a 13/32” collet. Unscrew the sheath
housing from it while simultaneously depressing the latch. This will
keep the flange on the nosepiece from being caught up.
STEP 6 (Only perform this step if the latch is damaged)
If you need to replace the latch on the sheath housing, place it over two
v-blocks. Hold a small punch or pin with a set of tweezers over one end
of the pin in the housing. Gently tap the pin out of the housing and
remove the latch and spring. The replacement latch kit is part# 40503.
STEP 7 (Only perform this step if necessary)
To remove the dog pins (40459) from the drive
plate, place the plate into the crows foot shaped
hole on your block (far left pic). Then use a thin
punch to drive the pins out of the holes. To remove
any of the bushing posts, place the plate upside
down over Hole #6 in your block (above right picture). Again
use a thin punch to drive the post(s) out of the drive plate. To
the left is a picture of the bushing and bushing post disassembled
from the drive plate.
STEP 8 (Perform this step only if bearing is broken)
If the small 40435 bearings on the drive ring spindle are damaged,
they must be replaced. Accomplish this repair by placing the
damaged bearing upside down in one of the holes on your block as
shown in the picture at left. Place a thin punch over the back of the
bearing post and tap it out. The disassembled bearing post should
contain the 40435 bearing, and a brass 40453 spacer washer as
shown.
The nose portion disassembly should now be complete. Line up your parts like that
shown in the picture on the following page. All of these parts are replaceable and all can
be ultrasonically cleaned.

Picture
Number Part Number Description
1 40443A Speed Change Collar (2-Speed)
2 40443 Speed Change Collar Screws
3 40493 Clutch Housing
4 40493A 2-Speed Clutch
5 40437B Drive Plate (shown with Bushing Posts (40460 &
Bushings 40461) Also note: the Clutch Pins (40459) are
inserted as well.
6 40494A Spindle Bolt
7 40437A Wide Drive Ring Spindle
8 40437 Wide Drive Rings
9 40449 Main Spindle
10 40432 Main Spindle Bearing
11 40464 Thrust Washer
12 40464B Metal Shim
13 40448 Loading Springs
Sub Assembly B Disassembly (Motor Housing)
(Note: most pictures are of a 40446 1-speed raceway, not the correct 40446A raceway)
STEP 9
After removing the two narrow drive rings, insert your
turbine raceway tool (00003) into the three holes in the
raceway. Unscrew the raceway from the housing. If you
cannot get the raceway to unscrew, put the threads of the

housing into a 9/16” collet. With the housing securely held, insert the raceway tool into
the raceway and unscrew.
STEP 10
Remove the vent plug from the housing. Like all threads on
this handpiece, turn counterclockwise to unscrew. Once the
plug is out, replace the o-ring (404072) in the rear of the housing.
STEP 11
To disassemble the turbine, place the drive ring raceway over the largest hole
on your work block (as shown). Then put your Lares disassembly tool
(00024L1) into the end of the motor spindle. Press the spindle and tool
through the raceway.
STEP 12
Now turn the partially disassembled raceway over (see picture). The front
motor bearing must be removed from the raceway. Use your Lares
assembly tool (00024L2) to punch the bearing out of the raceway. Always
replace these motor bearings when performing an overhaul. Place all of your dirty or
fouled parts in the ultrasonic cleaner.
Picture
Number Part Number Description
1 40438 Narrow Drive Rings
2 40446A Drive Ring Raceway (40446 is pictured)
3 40442 Turbine Spindle
4 40433 Front Turbine Bearing
5 40454 Impeller
6 40405C Rear Turbine Bearing
7 40424A 2-Speed Turbine Housing (40424 is pictured)
8 404072 O-Ring
9 40501 Shorty Vent Plug (pictured)

Sub Assembly B Reassembly (Motor Section)
STEP 13
Place the turbine raceway upside down on you work surface. Insert
the front turbine bearing into the appropriate hole (as shown). With
the bearing partially inserted, place a small dab of Loctite on the tip
of a needle and apply sparingly under the flange of the bearing.
Press the bearing firmly into the drive ring raceway and let sit.
STEP 14
After the Loctite has cured, center the raceway, bearing side down, over
Hole# 7 in your work block (picture at left). Place the turbine spindle over
the hole in the bearing with the fat side up. Put your Lares assembly punch
in the top of the spindle and press the spindle into the bearing.
STEP 15
Now center the impeller over Hole# 6 in your work block. Place the small
end of the turbine spindle into the impeller (as shown). Using the same
Lares punch, press the spindle into the impeller.
STEP 16
If you did not replace the rear o-ring in STEP 10, do so now. Then reinstall the vent
plug.
STEP 17
Place the rear turbine bearing (40405C) into Hole # 2 of your work block.
Be sure the balls in the bearing are face down. Put the small end of the
turbine spindle into the bearing. Use the Lares punch to press the partial
turbine assembly into the bearing.
STEP 18
Insert the raceway tool into the three holes in the raceway. Carefully begin to thread the
raceway into the motor housing. A good tip is to turn the raceway counterclockwise until
a click is heard. Then begin to thread the pieces together. Once started, thread the
raceway securely into the housing until it bottoms out.
STEP 19
Now insert the two narrow drive rings into the drive
ring raceway 180 degrees apart. Notice there is a
small cut out portion on the inside edge of the drive
ring raceway. This allows you to insert the narrow
drive rings into the proper position.

Sub Assembly A Reassembly (Nose Section)
STEP 20
Reinstall the latch kit back onto the sheath housing. Once
this is done, place the front spindle bearing into the
nosepiece. Depress the latch and screw the nosepiece back
into the housing. Firmly screw the two pieces together using two rubber strips.
STEP 21
Now place the main spindle bearing onto the back of the spindle.
Follow this by sliding the thrust washer and shim washer over the end
of the spindle.
STEP 22
Now insert the clutch into the clutch housing. Turn the
assembly over and place 2 dabs of green grease onto the
back of the clutch 180°apart from each other. This is where
you will now place the two loading springs.
STEP 23
At this point, hold the spindle assembly and clutch
assembly horizontally and opposite each other (far
left). Press them together and hold tightly while
screwing the spindle bolt into the spindle as shown
(near left).
STEP 24
Insert the spindle half way into the 3/16” collet. Now
tighten the spindle bolt, tightly, into the spindle (far left
picture). Remove from the collet. At this point you
can slip the speed change ring onto the clutch housing
and insert the screws (as shown above).
STEP 25
It is now time to install the three wide drive rings. Insert the wide drive
ring plate into your wide drive ring tool (00017). Follow that by spacing
the three drive rings evenly in the tool (as shown). Grooves are pre cut
into the tool and will properly space the wide drive rings.
STEP 26
With the drive rings properly placed in the drive ring
tool, lower it over the nose section (far left). Make
sure the three black bushings are out of the way of
the grooves where the three drive rings are to be

inserted. Once the two pieces are aligned, slowly lift the tool off of the drive ring plate.
Use a small flat screwdriver to press the three drive rings into the clutch (as shown
above). This will correctly insert the wide drive rings and plate into the clutch housing.
This tool does not insert the drive ring into a 2-Speed the way it does on a 1-Speed. The
tool will align them, then, using a finger, keep them in place and use the screw driver to
slip each one down separately.
STEP 26
You now have two properly assembled Shorty halves. Sub Assembly A
and Sub Assembly B. Place any spacing washers that may have been
present back onto the outer edge of the clutch housing. Now mesh the
two drive plate bearings into the two narrow drive rings in the motor
housing. Once these are correctly aligned, begin to thread the two halves
together. Be sure not too cross-thread the pieces. If the pieces seem to stop threading
together right before they look properly seated, STOP. You may not have the drive plate
bearings aligned exactly inside the narrow drive rings. Back the pieces a part 1/16th of a
turn and retighten. If they still don’t align, unscrew the pieces and start this step over.
Forcing assembly A and B will break the LocTite loose on the turbine assembly.
STEP 27
To firmly tighten the two assemblies together, once again, place the
sheath housing into the ¾” collet. Insert the spindle into the housing.
Wrap the motor housing with a strip of rubber and tighten firmly in a
clockwise motion.