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.

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.