Given some members requested this information, I decided to do a dedicated thread on how to lubricate the capstan bearing. It's an operation that I consider very important to any service done to a cassette player or recorder (being it a walkman, portable recorder or deck). NOTE: The pictures (3 out of 4) used in this thread are from walkman-archive.com There are 3 reasons I consider this to be important: 1. The bushing is made from brass, which is a soft metal compared to the capstan and will wear if the capstan is rotating dry. It's not something that will happen overnight, but I did repair units with many hours of use that had visible play in the bushing; 2. The increase in friction will increase the wow&flutter. It's not always going to be something noticeable, but given how simple the operation is, it's worth doing it anyway as maintenance; 3. On some units, this bearing came dry or almost dry from the factory; There are 2 types of flywheel support mechanisms: - older ones use a bracket retention system that is hold down with a couple of screws. This is a better system, as the thrust play is much lower and can usually be adjusted. - the second one is something that's either used in walkmans that need to be very slim and a bracked would not fit; or in cheaper units that need to save on BOM cost, hence eliminating the bracked altogether. In this system, the flywheel is held in place by a cut washer that sits in a groove that's cut on the capstan. NOTE: Pay attention, as there is at least one more washer besides the cut washer that you need to remove, sometimes 2 more. 1. After you remove the flywheel, I suggest cleaning the capstan with a cotton swab and IPA. It is very important that you use oil for this operation and not grease. Grease is very thick and will create a lot of additional friction inside the bearing. The type of oil is also important: you need to use a thin oil: watch oil is preffered. If you use engine oil, use something thin like 0W20 or 0W30. Modern engine oils are compatible with brass, so it shouldn't be any problems in that regard; However I do recommend using either watch oil or an oil designed for fine mechanisms. 2. Put oil only on the lower part of the capstan (the part that sits into the bushing, not the part that is in contact with the tape). At this point you can put the flywheel back and reassemble the cut washer or the bracket. In the case of bracket system, you will also need to lubricate the friction point (use white lithium grease here). 3. At this point put the unit in fast forward/rewind and clean the capstan with IPA 2-3 times, to get rid of any oil residue. If the pinch roller got oil on it, clean that as well. This part is very important, as you don't want to get oil on a tape (it will make a mess).
@Valentin I just happened to find your excellent post when trying to repair my Toshiba Walkman from the early 80's, which has a brass flywheel (with a bracket system) with a long metal capstan shaft. I was initially wanting to use some clear silicone grease on the capstan shaft which inserts into the brass bushing because I didn't want to have low viscosity mechanical oil possibly leak into the capstan shaft which touches the tape, even if I clean it up later. The Toshiba also doesn't have any tiny washer on the upper side of the capstan to prevent any oil leaks onto the tape area. I'm just wondering if this is really a good idea to use a low viscosity oil there? What's to prevent the oil from "travelling" when the "Walkman" is being handled in various orientations or just being used? Wouldn't the oil eventually migrate outside?
Incidentally, would something like this be alright to use (for the capstan shaft / bushing and also a drop on the motor shaft)? https://www.super-lube.com/multi-purpose-synthetic-oil-with-syncolon-ptfe-51010
Depending on the quantity of oil, some will get out. But after a couple of cleans capstan will remain clean. Best thing to do is after first clean check the capstan again after 10-15min of use and if there is oil at the base clean it with a dry cotton swab (while unit is running). Then repeat the process until there's no oil coming out. This will greatly depend on the amount of oil you put initially. Ideally, only a small quantity should be used and only put at the base of the capstan, not in the bushing. Indeed a washer at the top will help in this regard, but it's not really necessary. Besides, most devices with a bracket system don't have it. So as a conclusion it's ok and recommended to use a low viscosity oil in the capstan bearing. In regard to the Superlube oil it's probably fine but not sure about PTFE content. Would prefer watch oil to it. Its viscosity at 118cSt@40°C is more than double compared to Moebius 9010 watch oil has 52cSt@40°C. In practice, this oil will never reach 40°C, operating closer to 20°C (where viscosity is 3 times higher).
Hello, thanks for your post ! I think I made a mistake while adding a very thin drop of oil on the point where grease should go in case of a flywheel supported with a bracket... I did it on my sony D6C, which has a groove on the top of the flywheel so I believe that it could prevent it from getting out. Can I get away without opening it again ? Is there a real risk for my unit in my case ? Thanks for your time !
If you are reffering to the back side of thrust adjustment screw, the point of using grease there is because the contact area is very small and grease tends to stick better. There's no immediate risk if you put oil there, but in time chances are the contact surface will run dry as that oil will tend to spread a bit. Hence why I recommend taking it apart again and add grease instead. If you haven't done the thrust adjustment, an easier way to add grease would be to simply remove the screw, add some grease on its back then screw it back, adjust and lock it.
@Valentin one quick followup question: Is it necessary to clean the previous (old) lubrication from the capstan shaft + inside the brass bushing before re-lubricating? And how best to clean inside the small narrow bushing?
If you replace grease wil oil or the other way around, yes it is necessary to clean the old lubricant. The inside of the brass bushing can be cleaned with a cotton swab where you pull part of the cotton outwards to create a thinner part which will fit inside.
