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R27 Horn

You can talk to Craig "Vech" Vechorick at www.benchmarkworks.com. He offers a free tech support line.

Most of the horns can be repaired. There's an adjusting bolt on the back of the horn, and the horn will only sound when the bolt is set within a relatively small range.

I suggest you remove the horn to a workbench, along with a good 6V battery. Wire the horn terminals to the battery terminals in a way that is easy to make and break the connection. Then, with the battery connected, turn the bolt until the horn sounds, and adjust for the loudest point.

If your horn can't be made to sound, then your horn may in fact be dead. One thing to look at, however, if someone has been into the horn, is that the sounding diaphram has to be aligned correctly with the electromagnet mounted inside, to the base. A careless tinkerer may have reassembled the horn in a misaligned way which will guarantee that the horn won't work.
 
This is what I did with mine

I don't know if the horn on my R26 is original or not, but it was rusted and didn't honk too well

434424518_xfiKW-M.jpg


Anybody know if this is the "correct" horn?

434424590_bXZP7-M.jpg


Anyway, I took it off the bike, disassembled it, sanded and painted all the parts but the part that says "Bosch," and put it back together. I figured if I messed it up, I could just buy a new one.

434424625_deaSG-M.jpg


I adjusted the nut until I could get an audible beep. According to the guy who performed the safety inspection, there is no decible requirement, just that it is audible. :D
 
As background, the way these horns work is as follows:

When the "key" is on, power is supplied to one of the two terminals of the horn. It doesn't matter which. The other terminal is wired to the horn button on the handlebars, and, when that is pressed, it grounds that side of the circiut to the handlebars.

This causes current to flow inside the horn. There is an electromagnet inside, and the current magnetizes it. The magnet operates on the steel diaphragm, pulling it backwards. The diaphragm has a part attached to it that, at a certain point in the diaphragm's movement, breaks the circuit, which causes the electricity to stop flowing, the magnetism to cease, and allows the diaphragm to spring forward. As it moves forward, the circuit is reestablished and the cycle repeats.

The adjusting screw on the back of the horn controls the point along the diaphragm's movement where the circuit is broken. If it is far from the ideal point, the cycle never gets started. Only a small range of adjustment allows the cycle to repeat, and repeat in the frequency range to produce the honk.
 
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