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Reference: See
www.miniplane.com
for parts description and
www.Top80usa.com for purchasing spare parts. The ready supply of
U.S. held parts for this machine is one of its draws.
See also
Specifics on the Top 80
There are at least three types of redrives for
the Top 80 and several different gear ratios. The ratio is the number of
teeth on the big gear divided by the number of teeth on the small gear
(see sidebar).
Besides the usual hand tools, here are some
extras that will be helpful:
-
Gear puller to pull bearings off of shafts.
Auto parts or hardware stores.
-
Retainer Ring pliers, found at hardware
store, to spread apart and remove the retainer ring that holds the
small gear on the clutch shaft.
-
Claw hammer to remove the small gear from the
clutch shaft.
-
Rubber Mallet to pound various parts without
damaging them.
-
Deep well
socket set or pipe to protect inner/outer races when applying pressure
to bearings.
-
Valve Lifter Puller for removing the large gear back bearing. Find
online, e.g. Tooltopia.com.
-
High temp grease and a tube of high temp gasket
maker. Find at hardware stores.
-
Small bearing press. Find at hardware stores
(I found at sears).
1. Disassembly
  The hardest part is getting
everything apart without damage. Having the right tools will be
invaluable. . Namely a bearing press hardware store), gear puller (hardware
store) and valve lifter (auto parts store). Here is the process.
Before disassembling, note how far in the
clutch lip sits in its housing (above second picture). That's how far
you'll need to pound it during the latter steps of this process.
First you must separate the case halves without
damaging the face. That face must maintain a seal to prevent the grease
(or oil) for leaking out.
-
Loosen the six connecting bolts so that
about 3 threads are showing. Use a hammer and tap each bolt to
separate the case halves by an 1/8th inch or so. Don't hit the bolts
hard lest you booger their relatively weak aluminum threads. Finish
pulling the case apart by prying with some form of wedge while
protecting the cases' edge face. The prop side spline (part of the
large gear) has a bearing in the case which may pull out of the case
when you separate the two halves.
-
 Removing the retainer ring from the small
gear then pull the small gear off its spline. A claw hammer is helpful
but make sure it doesn't damage the case's edge face. The clutch is
then held in place by two clutch bell bearings. Remove the clutch bell
by pressing it out or heating the housing unit.
Bearings
There are 4 bearings. Sealed bearings are
required wherever they would expose the redrive's insides to the
exterior. When working with bearings a few cautions are in order.
-
Don't inflict excessive
heat on new bearings. Using heat to remove old bearings is ok since they will be
discarded but allowing new bearings to exceed about 300° will be
ruinous. An example would be putting new bearings in a heated which
will quickly transfer the case heat to the bearing without proper
cooling.
-
Never apply force to just
the inner or outer race if the resistance is on the opposite race. It
can cause invisible damage to the bearing, dramatically shortening its
life. Even for old bearing it's
can rip it apart such that only the stuck race is left as bearings
spill out.
2. Bearing Removal
Removing the large gear back
bearing is the easiest. Heat up its aluminum cover until the bearing
falls out. It takes at least 350°F. Broiling in an oven works. Heat it
up to its maximum temperature, put the case on a pan upside down and
insert. The bearing should drop out. If the bearing doesn't just fall out, you'll need
the valve lifter puller tool mentioned above. If the bearing drops out
too easily (when the case is barely heated), it's possible the previous
bearing spun its outer race in the socket. That would be bad. It must be
press fit reasonably tightly.
 For
removing bearings from gear shafts, use a gear puller like the one shown
at left.
The two bearings for the
clutch bell (the lowers) can be tricky. If they don't fall out
when the case is heated, use a bearing press. Warm the case then press
the bearings out.
In a worst case scenario,
where a bearing is nearly fused onto a shaft, it can be removed by rapid
cooling. Heat it up with a torch until it's red hot then pour ice water
onto it. That will crack the inner race which should allow to slide off.
3. Bearing Replacement
Replacing the bearings is
easier but carries its own risk. Make sure all the bearing sockets are
completely clean. Heat the case up to at least 400°F. Immediately after
removing the case from heat, use a pair of needle nose pliers to slide
the bearing into the socket by its inner race making sure to keep the
bearing vertical with the edges and working it down if necessary. You
can use a flap round tool (like a socket from a socket set) to pound
them down but make sure you contact both bearing races, inner and outer.
Once inserted, quickly cool the bearings
to prevent heat transfer from the hot case. This can be done using a
slightly damp
cloth but you've only got about 15 to 20 seconds before the bearings
absorb too much heat. Avoid shock cooling the case, being cast aluminum,
it cracks easily. Another good method is bowing air on them after
insertion. That helps reduce the chance of introducing moisture, too.
A problem bearing may be
pressed in using special flat tools that hold it exactly flat to the receiving surface.
Again, be sure to press against the whole bearing, not just the inner
race.
5. Reassembling
Once all four bearings are in place, press the
clutch through its two bearings. Support the bearings with a deep well
socket something similar and use the mallet to pound the clutch shaft
down through. The bearing must be supported by its inner race when you
do this. Slide the small gear onto the clutch spline and insert the
retainer clip.
1
2
3
4
5
Press the large gear into the case large gear
bearing. You're almost done. It should now look like picture 1. Apply
grease (pic 3 for one type) all the way around both gears then spin the
gears. Grease will squeeze out which is OK. Too much grease will create
more friction ergo more heat so don't overdo it (pic 2). Finally spread
high temp gasket maker (pic 4) evenly around the cover's face (pic 5),
wiping off excess, especially from the inside. The gasket sealer may not
be necessary if your face halves are perfectly flat.
Put the case halves together. They won't just
slide together because the large gear shaft must slide in the cover
bearing. You may have to use the mallet. Wipe off excess gasket
material.
For closing the case, you want bolts that are
long enough to engage all the threads without bottoming out. Trying to
tighten a bottoming bolt will destroy the soft aluminum threads. You
would then have to use a helicoil or other means to fix the thread. I
recommend lock washer because then you can see the lock washer flatten.
Clean everything up and voila, fresh redrive! |
