PPG Troubleshooter

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Motor Problems

Redrives & clutches

 

Propeller Problems

 

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Chapter 12: Setup & Maintenance
Parts & Service
Tools

Tips on non-motor hardware improvements

Winterizing your Paramotor by Alex Varv

 

Rebuilding a Top 80 Reduction Drive (Redrive)

Specific instructions for rebuilding the Top 80 Redrive

Reference: See www.miniplane.com for parts description and resources for where to purchase 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).

1) Geared redrive with clutch. The clutch mounts to the motor's output shaft. 
2) Parts description for original Top 80 geared reduction drive.
3) Old style Top 80 reduction drive. Reduction ratio (aka gear ratio) is the number of teeth on the big gear divided by the number of teeth on the small gear. If the big gear has 40 teeth and the small gear has 10 teeth then the ratio is 4:1, pronounced "four to one."

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.

  1. 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.

  2. 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 350F. 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 400F. 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!

 

 


© 2016 Jeff Goin & Tim Kaiser   Remember: If there's air there, it should be flown in!