The following excellent article has been contributed by Mike Davis, and is reproduced here with permission. These instructions are also applicable to the HP-65.

The photos below may be of use to those of you who wish to repair the gummy wheel on HP-67 card readers. The focus of this page is to show how and what to replace. It is intentional that it does not provide suggestions for dealing with the label or the clutch. I do not have a solution for these two areas that I want to commit to, at this time. It is also not a tutorial on how to treat electronic devices. You should consider your 67 as static sensitive and treat it accordingly.

If you have signs of gummy substances on your cards after running them through the reader, the drive wheel may need to be replaced. Other signs are erratic card movement, no movement, slow movement or errors.
The first thing you must do is to remove the case back. This is not difficult but there are some precautions you must be aware of. 1) Do not pry, from the sides or top, to remove the top 2 screw hole plugs. 2) Be careful in lifting the label corners. 3) The feet, at the bottom, do not come off. Just lift outside edges.
Here is what the gummy wheel typically looks like.
Remove the 6 screws shown. You can lift the motor drive circuit board where it connects to the main circuit board. This allows you to remove the main PCB and easier access to the upper right screw, which is under the circuit board.
After you remove these 6 screws, the interior electronics and boards can simply flip out to the right as shown. Be careful, the power switch and program switch contacts sometimes stick to the keyboard PCB. Remove these and set aside so they don't get lost.
Slide the top half (part with keys) off to the side until reassembly is needed. You may decide that you wish to clean keys, etc. Make sure you know where they go before you remove them (get a photo). The keyboard matrix can now simply be unfolded to the left as shown.
Remove only the 5 screws shown in the photo. DO NOT touch the silver colored screws that secure the switch contacts to the board.
This is the last screw holding the card reader together. After you remove this screw, be careful not to pick things up. If you do, you may lose the small nylon balls that operate the switches. Almost everyone has lost one, at least once. You've been warned. You may also remove the gold contacts in the charger connector.
Now, simply lift card reader half, with the card head, and flip it to the left. You should locate the 4 nylon balls, the pinch roller and the two leaf springs. These have legs of their own and want to hide from you. Find them and secure them before you go any further.
It should be obvious what needs to be removed. Just look for goo. Remove the drive wheel by pulling out the slotted drive shaft, indicated in the photo. You can't actually see it in the photo. The yellow line points to it's location. Once you get this far, you'll easily be able to see it.
Now you can see why your card reader may not pull card through the reader. Carefully clean off all the goo. You may also want to check and see if any got into the hole in the center of the wheel. This can cause slow motor if you forget to clean it out.
I use pink silicone fuel tubing that I get at a local model shop. It's outside diameter is just about perfect and the inside diameter is slightly smaller than the outside diameter of the drive shaft. When you buy this material, check for concentricity of the hole to the outside diameter. If it's not concentric, you may get a variable speed when through.
Trim the silicone tubing to fit flush to the edge of the drive wheel. You don't want to leave tubing extending beyond the shaft hole or it might rub against the side of the card reader housing and cause slow motor. I don't use any glue. The fit is tight because of the size of the tubing.
Carefully clean all the interior parts of goo or other residue. Don't forget to clean the pinch roller slot. Sometimes goo get inside the two small depressions where the pinch roller sits. Install all 4 nylon balls, the pinch roller and the 2 leaf springs. You can also install the gold charger contacts, at this time.
Make sure that none of the wires are in the area that the card reader goes. Now, carefully, flip the card reader back into position. It takes a small pressure to the left. If you do this right, it will drop right back into place.
Before you lift anything off the table, make sure you put this first screw back into it's hole. This screw is the one screw that allows you to pick this up. Failure to do so, may result in those little balls taking wing. You've been warned again.
Now that the initial card reader screw is in place (see previous step), you may flip the keyboard half open and reinstall the 5 screws that hold the card reader together. Make sure that these 5 screws are all the way in. Sizes of screws vary and if the heads extend above the board, they will short out on the keyboard circuits.
Install the main PCB. Plug the motor drive board, into the main PCB. Install the "power" and "pgrm" switches and contacts. I apply a fresh coat of silicone grease to contacts. Then, carefully, place the keyboard and card reader into the calculator case. Secure it into place with the six screws.

Now that you have everything back into the calculator, you can perform a test before attaching the case back. It's relatively easy to hold the battery in place while running a card through the reader. If everything works, you can install the case back. If the cards don't read properly, you can try adjusting the shaft that goes through the reader. I usually start by turning the slot until the card does not easily push into position. I of course do this with no power initially.

Copyright (2001) Mike Davis
Send comments, suggestions or corrections to Mike Davis

I only have two suggestions to add: first, when I have difficulty adjusting the reader so that it pulls the card through smoothly, I sometimes disconnect the motor from the control circuit (some soldering required!) and apply a 1.5V power source directly to the motor terminals to test. Second, when the switch contacts do not seem to operate correctly, I attach a DMM (in short circuit test 'beep' mode) to the appropriate terminals at the end of the keyboard PCB, pull a card through manually, and test for a good contact as the individual switches are reached. These methods are useful because they let you perform essential tests without having to partially or completely reassemble the calculator.