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Oil for plain bearings
Hello all. I am looking for some advice on oil for sintered bronze bearings in an old motor(1/2hp). The manufacturer's plate says to add 15 drops of non-detergent SAE 20 oil every year. On a plain bearing with no force-feed lubrication, is detergent(motor) oil going to harm the bearings/journal? The only comment I have found online other than do/do not use, is that the detergents may dissolve the insulation on the windings. Another comment was that if put in a gear box, detergent oil will foam. I had a friend who used GTX20W50 in his car gearbox without any issues. I have a bench grinder with a worm drive for a wet wheel. I put a clear cover on the drive and put gearbox oil in. It foams away merrily!!
I understand most forums are run by self -styled experts( e.g. bobistheoilguy)who have little to no actual knowledge.
11 Replies
2663 Posts
I'm not an expert either, but as an inveterate tinkerer with older kit, here are some thoughts.
The note that 'oil may damage the insulation' is certainly true of older insulations such as rubber and waxed paper, I suspect it is not true of modern polyurethane based enamelled wires and plastic insulation - indeed oil immersion for cooling coils and other electronics is common and I have used old engine oil for this (tip - it's a poor choice at RF... better to use an ester like Midel...).

So, what is the construction of this old motor ? (how old - I have a cotton and paper insulated pre-war machine under my lathe, and that works just fine on 20/50 oil, (I still have about 95 % of the oil left in the container as takes a quick 'bloop' a few times  a year )but I am careful that it only goes onto the bearings.) The idea of sintered bronze (as opposed to the solid cast bearings pre about 1930) is that the oil holds to the surface, so it sort of 'wicks in'  to the structure of the metal (a sort of absorbent sandstone of the metal world at a microscopic level) To that end the surface tension and viscosity of the oil at the running temperature are the key aspects.
I suspect the choice of a detergent or not is not so relevant in a bearing, as the idea of adding them is really for an engine  to keep the carbon in suspension until it reaches the oil filter.
If you are worried you are using the wrong oil, you can check to see if  the bearings heat up after a few minutes of idle running - when correctly oiled the shaft should be full supported on an oil film and run cool- - I'd expect it to stand several hundred PSI (estimate of the shaft to bearing contact area may be tricky without dismantling) of side load before the oil crushes out and it starts to complain by squeaking and getting hot.
You can certainly get non-detergent oils, at a premium, sold for old motorbike enthusiasts and so on, but unless this is a priceless heirloom, I'd try the common stuff first.
Now waiting to be shot down by others.
regards Mike.
The motor is a Dayton on my 1951 Southbend. It has rubber (not plastic) insulated wires. I use the recommended Mobil Velocite oil on the lathe bearings. I have found out that 3 in 1 sells SAE 20 electric motor oil. I will give it a try. The lathe apron, lead screw and drive spindle will get some multigrade. I suppose any oil I put on will be better than anything available in 1951!

These online forums are amazing. Here is what I have found out. Fram oil filters - useless(they do have a lawsuit for the filter media collapsing). But they make filters for Honda. For the last 20 odd years I have been told never to use Quaker State oil as it makes sludge(Castrol never does). but a friend of mine was told to use Quaker State in his Toyota because the 'waxes' protect things on start up. Now Pennzoil(owned by Shell) is second rate because their oil is made from natural gas. One bloke said his car makes a noise after 3000 miles. I always thought oil did not 'wear out.' It just got dirty.

What lathe do you have?
2663 Posts
Oil wears out at temperature by oxidation, and over time as the shorter more frisky molecules evaporate leaving the bigger ones behind, blended oils tend to become thicker and waxier.
Your machine is relatively youthful, my lathe is a 1921 or 22 Drummond B (early pre-cursor to the one that later became myford but belt driven and open gear train) but the counter shaft and pulley wheel for the flat belting is older though it has at some point been re-bored for ball races. Sadly in an odd imperial size.   The motor is an unrelated 1908 induction job with a centrifugally switched reluctance delay starter winding, and goes with a fair crack of the switch and a blue flash worthy of a dodgem car when up to speed, and it is time to disengage the starter. I do  suspect 50Hz may not have been the design frequency. The rope drive passes through two holes in a 1960s desk as the motor is beneath and the lathe above. The inrush limiter is an early 2000s attempt by me to stop it firing a B32 on start up.
Not a sintered bearing to be seen on that machine, all plain.
Welding up a decent guard for it all is on the list of things to do, as it does occasionally fire off the flat belting or the rope if things get a bit hard going, which is a touch un-nerving.
It is not exactly a classy installation, but it keeps proving itself very useful, and is easily repaired.
Roger Bryant
272 Posts
There are a lot of additives in engine crankcase oils which may or may not help your plain bearings. If you can get the correct industrial oil at a reasonable price I would use it. The industrial oils have a different additive package, often because they are expected to have  a longer service life. Automotive components are rated for a 3000hr service life.

Hobbymat MD65 owner.
Andy Millar
1732 Posts
Watching with interest, as I ought to be finding out more about this to keep mine running nicely!
1930s Portass 3 1/2 inch "Super" belt driven, plain bearings
1950s (?) "Rodney" stand alone miller, ball races
I got the Southbend from a friend for $450. I had been looking at some of the Chinese lathes. The problem here is that we do not have the option to purchase a metric version, only the 'sort-of-imperial' models. And the SB was cheaper. The bed is pretty worn but the spindle bearings are fine. I put new wicks in the spindle bearings and felts in the apron. I tried a new leather belt but am now using a spliced serpentine belt. It is much better than leather. much less tension needed and much less slip. Eventually I will put on an endless serpentine.
Old lathes and mills are quite affordable here. The curse is moving them. 1500kg of 60 year old iron costs the same to move as 1 year old iron!

Now to develop something simple to produce in my dotage to keep the wolf from the door - no pensions in private sector USA.

Your odd size bearings may still be available here in the US. If you need a set give me a shout.

I still find it hard to believe that a UK or US company cannot use Far Eastern castings to make a decent lathe as alternative to the 'all-Chinese' offerings. I am surprised India has not started to compete in this market.
Roger Bryant
272 Posts
Optimum in Germany produce machines in China with European quality control. I have read mixed reports but people seem generally satisfied.

I still have my Einhell branded mini lathe tucked away under some shelves but haven't used it for years. It required new headstock bearings plus some work on the tailstock before I could get satisfactory cuts. I also have a Proxxon FD150 for very small work and as a get me out of trouble when the Hobbymat is in milling mode and I need to turn up a spacer for something.

What sort of things are you intending to make? I try to repair broken things and also make small internal combustion engines.
Arran Cameron
432 Posts
There is a controversy whether vintage machinery is best lubricated with vintage lubricants, that were around at the time it was manufactured, or whether modern formulations are better.

I have some synchronous electric clocks and the manufacturers recommended using engine oil to lubricate the bearings with (the gears run dry) but this happened to be the single grade engine oils sold in the 1930s to the 1950s. Modern synthetic multigrade engine oils are unsuitable as they contain all sorts of detergents and additives that can damage the mechanisms and stain brass.
Arran. You might be able to purchase some rifle oil for your clocks. It has few additives and evaporates without leaving a film. Sewing machine oil is probably the same.
Roger: I use it to repair things. I have also made bee-mite fumers which you can sell. Most people around here are the throw away and replace types. 
Arran Cameron
432 Posts
Anthony Brooks:
Arran. You might be able to purchase some rifle oil for your clocks. It has few additives and evaporates without leaving a film. Sewing machine oil is probably the same.
They are a bit too fluid for clock pivots but are ideal for sintered bronze bearings as they soaks in well.

There was a graphited lubricant called oildag used to lubricate selectors in Strowger telephone exchanges that is ideal for lubricating small mechanisms with. Is it still manufactured?


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