Lubricate sintered bearings correctly

Lubricate sintered bearings correctly

Shafts in projectors and cameras are often held by sintered bearings – and nowadays these are usually completely dry and often resinous on the inside. Adding a few drops of oil here often only provides a very short-term cure and is not a real solution for maintaining lasting lubrication. Even if you can’t see it with the naked eye, sintered bronze is a very porous material that is designed to soak up oil and thus provide a depot effect. Unfortunately, sintered bronze does not absorb itself, and the capillary effect hardly helps here either, as the lubricants are usually too viscous for this.

In the following, I show how I treat sintered bearings with inexpensive home remedies to actually renovate them and ensure lasting lubrication. (Thanks to the “Zerspahnungsbude”, a bulletin board where I basically learned about this method a few years ago… but unfortunately I can no longer find the corresponding thread).

The first step, not shown here, is to soak the removed sintered bearings in white spirit or acetone for a while to dissolve the resin. If you have one, you can speed this up in an ultrasonic bath. Heating (film canister in a 60° water bath) also helps a lot here. It doesn’t hurt to let the parts soak for an hour. I discard this “pre-bath” afterwards.

I now throw the pre-bathed parts into a large syringe (20 ml or more), which you can get cheaply at the pharmacy.

Close the syringe. There are special “Luer-Lock” caps for this, but you can also remove the needle from an old cannula and simply weld it shut with heat.
(Fresh) acetone is now poured into the syringe again. The bearings should be covered a few mm with acetone.
Now insert the plunger, briefly remove the cap again and carefully bleed the syringe.
Once the syringe has been vented and resealed, the plunger is pulled to create a vacuum. You can now see the air bubbling out of the bearings. The stamp can be fixed with pliers or a vice, the vacuum should be maintained for a few minutes until no more bubbles rise. If you are thorough, you can repeat the process if the gumming was particularly bad.
The bearings must then be allowed to dry thoroughly so that all the acetone evaporates. I insert small “flags” made of wet wipe to help with capillary action. Heating (not too warm so as not to deform the bearings!) can also help. I always leave the bearings dry for at least one night. A few hours in the oven at 60° won’t do any harm either.
One day later, the dry bearings are put back into the syringe and this time covered with lubricant. Hydraulic oil is usually well suited for sintered bearings. Original lubricants are usually no longer available anyway. My standard oil for bronze bearings is HLP 22, which was recommended to me in the Dual forum. Available in every DIY store.
Here, too, the air is vented, sealed and a vacuum is slowly built up.
If you have cleaned them well, you can practically see the air bubbling out of the bearings! Hold this vacuum for a few minutes as well.
Tiny individual bubbles continue to rise for quite a while. After all, the oil is viscous. I wait here until no more bubbles appear.
No more air bubbles to be seen. Now the vacuum is released by loosening the plunger. Attention: The bearings should always remain below the oil. During this pressure equalization, they fill up completely with oil.
Without a vacuum, I leave the whole thing to stand for a few minutes until the bearings have completely soaked. You can also build up a little pressure (but hold the cap of the syringe firmly!)

That’s it! The air in the syringe now clearly shows how much oil has gone into the bearings. If you want, you can also weigh the bearings before and after, but why? Full is full. The remaining hydraulic oil can be collected and reused.

If you want to relubricate “lazily” after a few years, be sure to use the same oil. Mixing different lubricants should always be avoided if possible.

Friedemann Wachsmuth

Schmalfilmer, Dunkelkammerad, Selbermacher, Zerleger, Reparierer und guter Freund des Assistenten Zufalls. Nimmt sich immer viel zu viele Projekte vor.

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