Best lubricant for small gear reduction motors??

[davefr]

I'm seeking recommendations for an oil to use in miniature timing motors which I rebuild. Up until now I've used M1 0W-20 and wonder if there's a more appropriate product. (ex: synthetic ATF??)

These motors turn at 3600 RPM and reduction gearing brings them down to slower speeds such as 1 RPM. They only contain about 1.5cc of oil and the bearings are lubricated by capillary action.

They run at about 100 degrees F. They run 24/7 and should last for many decades.

Proper viscosity should be approx. 35-45 cSt at 40 degrees C.

M1 0W-20 has worked just fine and is far superior to the original oil these motors were manufactured with but I'm always looking for improvement. Would ATF be better??

I'd like something I can purchase by the quart.

TIA

 

[SuperDave456]

Looks primarily brass or bronze.
Do you know exactly what are they made out of?

The reduction gears that I am familiar with run submerged in gear oil. Similar construction, but they run in a sealed environment at room temperature. They may get warmer during the summer with lots of use (100+ degrees in the shop, plus load perhaps 120 degrees F)

However depending on the application, and if the components are sealed, gear oil may be a bad choice as that stuff STINKS.

Engine oil has all kinds of additives that are designed for use inside of engines. Additives that are used to protect against blow by of combustion particles which are not needed in a sealed gear based environment.

This is also why you see so many Sulfur additives in Gear Oils, that make it smelly, but also are Extreme Pressure additives that should not be placed in an engine.
Sulfur extreme pressure additives + heat + water (a byproduct of combustion) = sulfuric acid.

However, these smelly additives work extremely well in Gear Boxes.

One more thought.
If these devices are used indoors go with a Motor Oil. You spill Gear Oil in your house you will never get that smell out and your Wife will kill you. (my wife had a fit that the garage stank so bad when I had a bottle leak).

 

[davefr]

The gears are a combination of brass, phenolic and plastic on stainless steel shafts. The bushings are usually bronze.

The gears are not submerged in oil. There's only about 1mm of oil in the bottom of the case. It's fed up to the bushings by capillary action. (ie the sandwiched plates have a small gap between them that's actually a tiny reservoir of oil)

These units are sealed (not hermetic though).

I agree that motor oil might not have the best additive package for these motors. But whatever lubricant I chose, it has to be very light.

 

[SuperDave456]

The Phenolic and Plastic would worry me if you put Gear Oil in it.

With the information you have provided anything in the Synthetic 20 weight sounds good.

BTW, my brother is a Professional Tuba player. He uses pure Mineral Oil on the Valves of his Tuba's. Considering that $10,000 for a Tuba is around the average price, and $30,000 is not unheard of, this is saying something for an oil that needs to be light and non-toxic.

If you find that the 20 weights are to thick, or you just want to try something different. Hop on down to your local Pharmacy and pick up some mineral oil.(It is also used as a laxative.)

The stuff is thin like water, but also boils off quite quickly.

You oil Tuba valves every other day depending on how much you play, although they do get soaked in spit, hence the spit-valve for drainage (found in every brass instrument).

 

[Gabe]

What about air tool oil or Super Lube 51010??

 

[Tempest]

The M-1 0W20 is probably not a bad pick. The ATF would be worse in my opinion as it has lower AW and other additives. The motor oil will have a good amount of anti-oxidants and other adds to help keep it lubricating for some time, especially at only 100F.

Brass and plastic indicates relatively low loads. Silicone is ideal for lubricating plastic, but if the same oil lubes the stainless shafts in the bronze bearings, this won't work.

Quote:
The gears are not submerged in oil. There's only about 1mm of oil in the bottom of the case. It's fed up to the bushings by capillary action. (ie the sandwiched plates have a small gap between them that's actually a tiny reservoir of oil)


This makes me think that the gears are self lubricating?

 

[camelCase]

If that gear set requires a 35-40cSt @ 40ºC and your using SAE 20wt gear fluid - your viscosity is a tad too high. 20wt is usually around the 50-80cSt level.


You don't want to use EP additives in this gear set. One reason is they don't play well with yellow metals. The second is they are better for shear loads (think bevel gears in a transmission) than spur gears. This is why many lathes and mills that have spur gear setups use a lightweight hydraulic oil in many cases. They are also lubricated via capillary action (oil "climbing" the gears).

If I was you, I'd pick up either a high vis hydraulic fluid (32 or 46cSt) or a low viscosity ANTIWEAR gear fluid. Antiwear additives will play nice with those yellow metals. I can't recommend a fluid directly b/c of forum rules - but there are plenty on the market. With such a low charge quantity - I'd get as high of a grade fluid as you can. The higher VI that you'll have with a better fluid will maintain that ideal range of viscosity that's needed for the capillary action to work correctly for the designed gaps. The operating temperature isn't much to worry about being at 100║F - but you definitely want a good antioxidant package if you want the same fluid to run 24/7 for a decade.