Molybdenum Disulfide Grease

Several times in earlier sections of this web site, I mentioned the need to grease the bearings and other parts of the helicopter on a regular basis. Back in the old days, when one had the oil changed, one also had the car “greased.”  Technology has replaced the need to grease ball and constant velocity joints, and to some extent, that is true with modern helicopters.  But back in the old days, the H-2 and H-3 had many, many bearings and other rotating parts that had to be greased regularly.

The specified grease was a molybdenum disulfide compound that retained its lubricity when hot. We called the stuff “molly D” and the grease still is available today.  Before I sold my tractor in the summer of 2013, I bought a commercial version in an auto parts store to grease bearings in the steering gear, drive shafts and other areas.

As a grease, “molly D” is really good stuff, but has one ugly characteristic. Somehow, I think the individual who specified “molly D” did understand what happened when “molly D” was exposed to sea spray and salt air.  As ‘molly D” was heated, the grease reacted with the chlorine in the salt air and water and turned into a mild form of sulfuric acid.

I’m no chemist, but sulfuric acid even in its mildest form is very corrosive and when an acid comes into contact with aluminum and magnesium alloys, corrosion occurs. Guess which helicopters had aluminum skins and were full of castings made from those metals?

So, we were always giving the helicopters a fresh water bath to minimize the effects of “molly D.” Or, we flushedout the old grease and replacing it with new grease. And yes, “molly D “has its unique odor and a practiced nose could tell the difference between cold and hot molly D.

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