Rebuilding FIAMM Air Horns

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bartigue
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Rebuilding FIAMM Air Horns

Post by bartigue » Sat Jul 06, 2019 4:17 pm

A good project for my son today, rebuilding the air compressor and cleaning up the original FIAMM air horns for the 69 Spider. The compressor is a rotary type with the electric motor on the bottom and the rotor and blades on the top. First off, we removed the top of the compressor to expose the air input and rotor assembly. Top off, it looks like this:

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The three blades and ball bearing typically fall out when turned over. Note the assembly in the picture above is wrong - the blades each have a beveled edge that follows the curve of the bore. This unit must have been "serviced" before. A suggestion prior to disassembly is to spray oil all over this stuff, then gently pull it all out. Make sure you catch the little bearing. Note the air input side has a metal "air filter" (a screen which is typically filthy), a spring that is smaller on one end than the other, and under the spring it should have a gauze pad soaked in oil.

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It works like this: When the rotor spins the blades are forced against the bore. Air is drawn through the metal filter and over the oiled gauze into the air chamber, where it is compressed as the rotor turns. The oiled pad serves to lubricate the rotor. At the smallest point of the bore, the chamber just before the metal filter, air is expelled into the brass nipple leading to the air horns.

The important bits:
  • The exterior housing is typically filthy. Clean it thoroughly before disassembly. We used a can of carb cleaner and a brass brush on a dremel tool. On low speed it does not mar the aluminum
  • Use carb cleaner to spray through the mesh filter until you can see through it. If you don't have that filter then you can make one from a piece of brass or plastic insect screen
  • The gauze is probably junk by now - we replaced it with cotton medical gauze. You can use a bit of a t-shirt or towel.
  • The aluminum FIAMM used must have originally been coated with something but after you clean it up it will oxidize in about 2 minutes. We used a very light coat of aluminum colored caliper paint to seal it.
  • There is a plastic plug in the side of the unit. You can use electric motor / electric contact cleaner in a spray can to clean it out and drain it. We sprayed a bunch in there until what flowed out wasn't carbon colored. We couldn't get the motor out otherwise and didn't want to force it and risk breaking the plastic base.
Once reinstalled make sure you keep the unit oiled. Use any kind of oil, 3-in-1 works perfectly.
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Brad Artigue
1969, 1969, 1970, 1979, 1980, 1981, 1982, and 1982 124 Spiders
1969, 1970 850 Spiders
77 X1/9
http://fiat.artigue.com
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18Fiatsandcounting
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Re: Rebuilding FIAMM Air Horns

Post by 18Fiatsandcounting » Sat Jul 06, 2019 8:57 pm

Thanks, good to know, and I need to place this on my "to-do" list, as my horn takes a second or two before it builds up enough speed to push enough air to operate the air horns. Not a calamity, but when you need the horn, you need the horn to work NOW.

-Bryan
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bartigue
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Re: Rebuilding FIAMM Air Horns

Post by bartigue » Sat Jul 06, 2019 11:00 pm

The delay can be electrical or pneumatic. In the case of this car the pump took about 3 seconds to build up any pressure, and the horns were full of mud (I think from an insect, it took a week of soaking them and eventually mounting them to a pressure washer to get it all out). Take it all apart, it is quite easy, and clean out the horns and diaphragms. Then clean up the motor.

With the motor we found that oiling everything pneumatic and the electrical cleaner on everything electric, then letting it dry and reassembling, then letting it run off of a battery for about 30 seconds at a time (resting in between because really I don't know what these were designed to run for) really got it running right. The delay between application of power and noise from the horns is less than a second now. And it's loud as hell.
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Brad Artigue
1969, 1969, 1970, 1979, 1980, 1981, 1982, and 1982 124 Spiders
1969, 1970 850 Spiders
77 X1/9
http://fiat.artigue.com
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fiatfactory
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Re: Rebuilding FIAMM Air Horns

Post by fiatfactory » Sun Jul 07, 2019 8:08 am

Isn't there supposed to be a spring clip behind each of the vanes (in the slot of the rotor) to hold the vane in light contact with the body ... just like every air / hydraulic rotary pump I've ever rebuilt ... though it's been a loooong time since I had a Fiamm air horn rotary pump apart so I can't say for sure...

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Re: Rebuilding FIAMM Air Horns

Post by spider2081 » Sun Jul 07, 2019 9:20 am

Thanks for sharing this Brad
Isn't there supposed to be a spring clip behind each of the vanes
Looking at the first photo the working vane is all the way against the rotor (bottomed out). Also if the vanes are spring loaded out of the slots the non working vanes could move too far out of the rotor possibly causing binding.

Centrifugal force allows the vane to slide out of the rotor and the outer housing forces it back into the rotor. The rotor spins in one direction this can cause wear on one of the vane's sides. (scalloping) The vane can also wear in length. The combination of wearing in both areas can cause the rotor to jam. The air in port on the pump is very important. It is actually a vacuum so unfiltered it draws unwanted stuff into the pump. The filter Brad describes is very important. It protects the vanes by providing clean air.

I don't know much about the horn pump but I think a rotary pump that can be run continuously would have cooling fins on it. So I think Brad is correct in intermittently operating the pump.
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Re: Rebuilding FIAMM Air Horns

Post by fiatfactory » Sun Jul 07, 2019 9:39 am

There is usually a spring on a rotary vane pump to maintain contact of the vane to the stator before centrifugal force takes over... sometimes it's a bent spring clip, sometimes a coiled spring set into a recess... just saying as I recall this from my apprenticeship days, and it was one of the questions in the pneumatics / hydraulics certificate 4 I did a few years ago.

Just for interest sake I'm going to strip one down this week and have a look.

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Re: Rebuilding FIAMM Air Horns

Post by bartigue » Sun Jul 07, 2019 2:31 pm

This is the 2nd one I've rebuilt and neither had any spring behind the fins. They just slide out under force. That little electric motor produces a ton of force and those fins come flying out. I've also looked at a few pics of other people rebuilding the FIAMM motors and they don't have springs either.

The only reassembly question I've had is should the exact location of the gauze; I install it under the little oil cap, which is where I extracted it from (under the conical spring and after the metal mesh filter). In some pictures I've seen the guys don't have the metal screen and have the gauze jammed against the air hole. Which, in my view, can't be right as an oiled pad will just clog airflow.
-----------------------------------------------------------
Brad Artigue
1969, 1969, 1970, 1979, 1980, 1981, 1982, and 1982 124 Spiders
1969, 1970 850 Spiders
77 X1/9
http://fiat.artigue.com
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