Horn stopped working… Broken bolt?

[Willsmotorcycle]

I had the ST out the other day to scrub in the new tires, went to tap the horn and heard a faint moan. It’s raining today and I was thinking let’s pull the fairing and see what’s going on in there as my Hella lights start flashing when hot also.


Nothing seems unusual here

Ahhh there’s the problem, probably. I have know idea how long this has been broke. I’ll put 12v to her when people wake up around here.

Any ideas how that could sheer off?

 

[Obo]

The bolt seems to be excessively protruding from the boss where it sheared.
For one, that could not have made the ground wire very effective.
I also don't know that that metal tube with the flat end that said bolt also runs though, does. Fairing framework?
If that tube moves, or could move, or take a good push/whack, and was down near the head end of the bolt, you've got a great lever for snapping off a bolt at the boss.

 

[SMSW]

Where is that bolt on the bike and what is it holding together? Bolts usually hold two pieces together tightly - the threads screw into a mating hole and the head presses tightly on the second piece. Your picture shows a flattened piece of pipe with a hole through it some distance away from the threaded boss. This acted as a lever, bending the bolt at a stress raiser - the last thread outside the boss and it snapped. Over time, you had work hardening and failure.

 

[dduelin]

That cowl stay bolt should be 12mm long, not 45-50mm long. I don't think it could have secured the stay against the frame. Snapped bolt is likely not the one that should have been there. What is the slightly curved piece edge-on in the middle right of the image?

 

[Willsmotorcycle]

The bolt seems to be excessively protruding from the boss where it sheared.

Where is that bolt on the bike and what is it holding together?

That cowl stay bolt should be 12mm long,

Looks like part 9 and 15
The bolt holds the stay to the frame, I think @Obo is on to something with a great lever. Not sure if it was over time or an incident with a pot hole. I know the grounding failure was related to the horn failure, and intermittent because I had lights the day before. Im certainly leaning toward a big bump with a long lever and excess weight on the stay. Thank you gentlemen for looking.

What is the slightly curved piece edge-on in the middle right of the image?

That's the inner cowl Dave, it looks weird in the picture.

 

[Andrew Shadow]

Assuming that the correct parts were in there to start with my guess is that the screw worked loose for whatever reason and backed out of the threaded hole. This allowed the frame stay to move outward significantly increasing its leverage on the screw. The frame stay was then no longer kept tightly in place and could move. The stay kept moving levering the screw back and forth until it finally failed.

 

[Paul]

I would relocate the ground wire. The cowl stay is basically a structural component and needs a solid mount. A squishy copper ring terminal under the bolt head will affect the clamping force. You can see that the bolt was cracked for a long time between 6 and 12 o'clock before it let go.

 

[Willsmotorcycle]

Assuming that the correct parts were in there to start with my guess is that the screw worked loose for whatever reason and backed out of the threaded hole. This allowed the frame stay move outward significantly increasing its leverage on the screw. The frame stay was then no longer kept tightly in place and could move. The stay kept moving levering the screw back and forth until it finally failed.

This is the most likely scenario. Thank you.

 

[SupraSabre]

Interesting... I think that's where I have put my grounds for the horn relay. I'll be sure to check those, next time I remove the fairings.

 

[jfheath]

Personally, I’d run an extra high current earth cable back to the negative post of the battery, rather than assuming that the one that is fitted between chassis and the battery can take the extra 20A (or whatever your horn requires). It is a hefty cable, but why rely on two frame contacts when you can have your own reliable one.
For all my accessories I have a single 28A lead to each of the battery posts, fused, high current connector and apart from the relay triggers - taken form the quartet harness connector, I don’t pass any of my power through the bike’s wiring.

I agree - parts 15 and 9 . The diagram makes more sense if you look at the same stay on the right side of the bike in the picture - near to part #11