I have been operating my O27 postwar layout for 44 years and it has 31, Marx 1590 metal frog O27 switches. Over the years I have learned from others and my experience several tips and ideas on how to improve and repair these reliable, available and inexpensive track switches and share them below. These 31 Marx switches are now very reliable and capable of handling Marx, Lionel, MTH and Williams train engines and cars.
Marx 1590 switches are made to operate with Marx double sliding pickups. The Marx switches have problems with Lionel style roller pickups which are narrower and have smaller area rollers than the Mark sliding pickups. The rollers have issues with the wider gaps with the Marx pivoting center rails and often get hung up and cause derailments.
Pictures of pickups on Marx 1998 engine top (3/8 inch W x 1 inch Long each) and Lionel caboose, on the bottom (3/8 inch W x 1/4 inch Dia)
Marx 1590 switches wider gaps can be reduced easily by installing a 3/4 inch pieces of a finish nail (cheaper) or a 027 rail pins in the two center rail ends of switch as shown in the following pictures. This fifty year old fix will fill the center rail gap and keep Lionel pick-up rollers from hanging up or losing contact on Marx 1590 switches.
The picture below shows the center rail of the straight track with one inserted pin (or cut off finishing nail) and switch in the straight position. Note how the pin fills in the straight center rail gap.
The center rail of the curved track shows the other inserted pin and switch in curved position. Note how the pin fills in the center rail of the curved section.
Later problems were had with some Lionel car electrically pickups hanging up on the single track end of some of the Marx 1590 switch center rail points causing derailments. This problem was solved by crushing down the top part of the center rail point by gently pounding it down with a small hammer or by grinding it off to a 45 degree angle. The smoother angle of the rail can be seen below.
Recently I had problems with derailing on one of my Wye switches causing a caboose pickup to catch at this same spot. I found a better cure than crushing down the rail point to be installing a 1/4 inch of nail with a rounded trip in the small piece if center rail shown below were the rail is rounded off (see picture below). Care must be taken to insure only about 1/16 inch of rounded nail is exposed and it must not hit the tips of the pivoting center rails.
Cleaning and NO OXing Marx 1590 Contacts
Engines or car pickups can intermittently lose contact when traversing Marx switches. The 31 Marx 1590 switch track contacts can get dirty or bent.
Check to see if the copper switch contact is bend down and not making contact with the contacts on the bottom of the rotating track section. A small screw driver can be used to bend the copper contact up to get better contact with moving contact of the rotating track section.
Picture of Marx 1590 switch rail copper contact strip. The two rivets below the copper contact are the contacts for the center rail. 
The track switch contacts can be cleaned with fine sand paper glued up to make two sided sand paper. It is used by pulling in both directions while working the pivoting track section to both positions. Then a little NO OX ID Special A contact conducting grease can be applied, with a small thin piece of card board, can be applied to both sides of the contacts to keep sparking down and contacts clean.
Picture of two sided fine sand paper strip cleaning contacts 
Non Locking and Slow Acting Marx 1590 Switch
Recently a Marx 1590 switch on the main board, inside loop bottom left inside to outside, would not lock and was slow. This is first such Marx switch failure in 44 years of operating this layout! About one half of my 31 Marx 1590 switches have a hole in the side of the switch mechanism cover.
Hole seen below is typical of the hole in 1/2 of the Marx switch housings:
I never noticed that some Marx 1590 switches had a lubrication hole until recently. The troubled switch did not have such a hole. To get access to the Marx switch solenoids and sliding mechanism, the switch must be removed from the layout, a real pain for many of them that are not near a curve. Then the two rivets must be ground out or cut into section with a pair of diagonal pliers to be removed. Next the 3 or 4 tabs of the housing must be bent and allowing the housing to be removed.
Picture shows the slide mechanism and arm to the solenoid piston that needs to be lubed.
I drilled 1/8” hole in solenoid cover long side 1-5/8“ from big end, ¼ inch from top, and sprayed WD 40, with the small application wand, left, right and down. This fixed the switch and it locks every time and fast. Later I found out about one half of my 31 Marx switch solenoid housings have a hole on the inside, side edge already that can be used to lube the slide mechanism and solenoid piston. Spay Silicone spray probably would have been better than WD 40.
You can see this hole allows good access to lube the moving parts inside the switch housing. Another switch with housing is shown below one with new hole drilled in the side
Interference of Trains and some Marx 1590 Housing
The below picture shows the corner of the solenoid housing was cut back (by black automobile) on two Marx switches to keeping the cow catcher of some locomotives from hitting the switch housing. This was necessary when two Marx switches are too close together. The switch housing was removed from the switch, the corner cut off with a fine blade hack saw and part of the removed housing was J B Welded back on to fill the hole left from corner removal. It is possible to do this with the switch in place on the layout. A Dremel Moto tool, with cutoff wheel, can also be used.
You can learn about how I built and operate my 027 postwar inexpensive layout with homemade $10 turntable and round house below with index on bottom of page 1, post 1: Page1, Post 5 has me touting and giving more information on the Marx 1590 switch
https://ogrforum.com/...fties-era-027-layout
Charlie
