Thunderbolt Siren Restoration

Thunderbolt Siren
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Siren Chopper
Chopper Housing

Siren Controls

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Civil Defense
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Civil Defense Museum

The Thunderbolt siren uses a rotator mechanism to turn the horn. The rotator is very simple in design using a 1/3 horsepower motor and a gearbox to transfer the power from
the pulleys to the rotator gear.

Rotator belt sideI removed the sheet metal box from the rotator assembly so the inside can be clearly seen in the pictures. The assembly is made up of the heavy steel section (still yellow) that attaches to the top of the pole. The rotator motor and gear box attach to a 1/2" thick horizontal steel plate that bolts to the yellow section. The pipe of the yellow section is a single piece that passes through the steel motor plate. The large drive gear sets down in a recessed area in the steel plate. The belt is adjustable with slots in the motor mounting bracket and the speed of the horn is changed by moving the belt to the different pulleys. The horn rotation can be set to 2,4, or 8 rpm. The boss sticking up from the drive gear is where the drive band (explained below) clamps too.

Rotator connection sideHere is the other side of the rotator assembly. You can see the fitting that the chopper motor wiring passes through just below the horizontal plate in the center of the tube. This fitting has a pass-through rubber seal and cap to keep the blower air out of the rotator box. Electrical hook-ups are on this side of the box away from the belt and pulleys. This photo was taken before any cleaning was done on the rotator parts.

Rotator Transmission ApartThe rotator gear box was leaking like crazy so I had to reseal it. I got a new input shaft seal and made new gaskets for it. The thing is like new inside and shows very little wear. Even though this siren is more than 40 years old I guess it has actually probably seen very little use.

Rotator with chopper housingHere is the rotator with the chopper housing installed. The chopper housing sits on top of the drive gear. The drive gear attaches to the chopper housing with a wrap-around "drive band" clamp that allows the housing to slip under high wind-loads against the horn. The Thunderbolt service manual says this is to avoid damaging the rotator mechanism. You can see the drive band at the bottom of the housing tube where it clamps to the gear. Click Photo To See Larger.

Painted rotator partsHere are the parts of the rotator cover after painting. The rotator sheet metal housing is in 5 pieces.

Repainted rotator gear and plateHere is the rotator frame and gear before I put the housing back together. Everthing is cleaned up and ready to go. I left the main rotator support it's original color. It took me about an hour to get the gear clean enough to repaint. That 30+ year old grease was really coated on the gear. I installed a new single phase 240 volt rotator motor and belt when I completed the rotator assembly.