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(text and photos Copyright © 2004 Joe 'Cuda') As our
Airheads gain in age and mileage, it's not uncommon for Fiamm horns to
get weak or cease working. Since the components inside are very robust,
usually the cause is just dirt and corrosion thus very fixable.
First,
let's go over how a horn works. The diaphragm that makes the sound has
a thick metal "wing" bolted to it's bottom. When the horn is activated,
electrical current powers a pair of electromagnets anchored down in the
horn body. This attracts or pulls down on the wing and in turn
diaphragm. Sticking out from the wing is a small pole. When this pole
hits the insulated contact arm, it opens the points. With the points
open, the current is interupted, the electromagnets become de-engerized
and the diaphragm pulls the wing and pole back up. When the contact arm
springs closed again, the whole cycle repeats.One cycle per second is a
Hertz and 440 Hz is A above middle C on the music scale. The /5 and /6 models
had 400 Hz horns. The /7 had a 410 Hz low tone and added a 510 Hz
"high" for dual Fiamm horns. All other models are listed as having a
single 335 Hz horn. If you go to duals, use a relay as described in the
Relays 101-103 tech articles.
If you have continuity between the
( + ) and ( - ) horn inputs, then you might be able to just turn the
screw on the back (often marked with a white dab of paint) CCW to get
it working (not CW). But likely it needs to be cleaned or has no
continuity.
1. You'll needed a multi-meter, philips (+ drive) screwdriver, wrench with a 7mm socket, WD-40 and some thin sandpaper.
2. Remove the four screws around the edge and carefully disassemble to avoid gasket damage.
3. Order of removal should be the horn shell, a paper gasket, the diaphragm, another paper gasket and then the horn body.
4.
Note how the wings off the diaphragm line up over the electromagnets.
If your diaphram is dirty or corroded, clean it gently so as not damage
any more of it's plating. Give a light spray of WD-40 or clear paint on
each side to inhibit future corrosion. Take care not to damage the
paper gaskets there to keep gunk out.
5. Note how the pole lines
up over the contact breaker. There should be brown piece of
non-conductive bake-lite on top of the contact spring where the pole
hits.
6. Note the order as you remove the coil screw's nut, wire ring, nut/lock washer, washer and insulating washer.
7.
See the points? Easy to spot for those riding '80 and earlier Airheads
with points ignition. If there's moisture in there, chase it with some
Water Dispersant test batch 40 (WD-40) and wipe away excess.
8. Open the points. Push down with screwdriver lightly on the contact arm as you push the screw stud toward the center.
9.
Cut some fine sandpaper (preferably wet/dry or thin hobby on plastic
backing) about 6-7mm wide and about 50mm long, or 100mm if doubled over
to sand both points at once as shown.
10. You may need to press down on points spring from the side to get the sandpaper in to start.
11.
One way is to put the sandpaper (black) in through gap: close the
points by pulling back on the screw stud, pull the sandpaper back a
bit, open points by pushing the stud forward, push the sandpaper back
in, close, pull, open, push, close, pull, open, push...
12.
Another way is to feed the sandpaper (red) looped under from side to
side. Though trickier, you can file the points like a shoe-shine.
13. When done, the points will likely not be centered over each other.
14.
Line them back up before putting the nuts and washers in pic 6 back on.
Recheck after it's back together that the points are centered and for
continuity across the points as well as between the ( + ) and ( - )
leads.
15.
Reassemble the horn. Hook up the multi-meter. The Radio Shack one's
nice because it beeps when you have continuity. Turn the adjusting
screw CounterClockWise just until the points open (infinite
resistance). If already open, turn CW until you get continuity (zero
resistance) and then back it off just a hair until the points open.
Using
gator clips and wire, hook the horn directly to a 12-volt battery,
preferably a car battery for it's larger reserve. Turn the adjusting
screw CW until the points close and the horn "wakes up" (always a bit
surprising) and adjust for volume and tone. If you turn it CW to far,
not only does it get lower and quieter, but the horn will stop working
which can burn out a coil as the points are no longer being opened; ( +
) going direct to ground.
Clean all connection and apply
electrical grease. Insulate ( + ) connector with some heat shrink
tubing. Install on bike. Test. Again, you want to incorporate a relay
if using more than one horn not just to save the horn switch on some
models, but to improve horn performance via it's heavier and more
direct powering. Other horn workings similar.
Comments? Questions? Deafness?
Joe 'Cuda' #3335
'78 R80/7 |
