Swing arm bushing failure

[egleaves_imp]

Picked up the bike and was finally able to see the broken bolt. The bolt broke off inside the nut! This is clearly beyond normal wear and tear.

The service manager has a background in....structural inspection...something like that....we didn’t get into it. Anyway, he told Honda that it appeared to be a manufacturing defect and they took him at his word and made good on the warranty. Now they want to see the bolt. Hopefully they’ll be able to do some forensic analysis to deduce whether this was an isolated case, or there’s a broader risk.

Early on I was told I could keep the old parts, but now Honda wants them as evidence. I totally get that. I was “allowed” to take pictures of it so I staged a small photo shoot at the service desk. Sorry for the teaser, but the only way I can manage to post pics is from my work computer. Have to do it tomorrow.

Egleaves
Did you check after Honda replaced the bearings and other elements of the swing arm, is there no play?
Perhaps the new parts were produced badly and the swing arm still has a little play. You have everything new. There is an opportunity to verify it.
Normally no one checks it when buying a new motorcycle.

Good idea, sync. I checked this morning and there is currently zero play in the swing arm to frame connection. It's tight.

As promised, here are some pictures of the broken bolt:

[peterbaron]

Is the broken nut/thread on L = SPROCKET side or on R-rotor -side ?

[egleaves_imp]

Is the broken nut/thread on L = SPROCKET side or on R-rotor -side ?

Nut is on the R side.

[max]

See if you can see the same thing that i can, notice the bright ring on the start of the conical part of the shaft?

Looks as if the nut "bottomed out" on that part, continued to pull on the thread and stretched it for no good reason.

Threre is no rust on the broken surface, looks a recent event.

A simple washer could have prevented this, which begs the question;
Has a washer been used originally but since been omitted for some reason?

Cannot remember if my bolt was hollow but don't think so.

edit; yup,it's hollow and no washer installed here either;



This would be impossible to spot by the assembler at the time unless he had a lot of experience and the guts to tell his supervisor on the line, in the meantime.........

Great shots by the way

[the Ferret]

That doesn't even seem possible to me, for the bolt (threaded tube) to break off inside of the nut, without the nut being unscrewed..

Max the threads do not look stretched to me, at least that I can see. Doesn't stretching usually show up as a narrowing of the bolt between the good threads (like a waist so to speak)

[max]

Ferret i just saw this but if you magnify the last pic of the threads you notice the extreme flat top of the threads as if they were "galled" which is what happens when a piece of metal interferes inside the thread when it is tightened and changes the shape of the thread.

These have been shaved off right to the very last bit of thread which is initially hard to see because it all looks the same, and the stretch would be too small to see before the break occurs, it's hardened steel and not very pliable.

But good point Mickey, well spotted !

[syncronizator_imp]

Swing arm play test:
1. https://youtu.be/KPcq2ThzrIc
2. https://youtu.be/IFl91Vi3BYA

[GoldOxide_imp]

Pretty darn good videos syncro.

They should get lots of play.

[peterbaron]

^^ +1

[max]

Good work Pawel, i was hoping you had vernier calipers to measure the sizes, nice video's thank you.

The reason it's called a "shim" is because if you want to fill a small gap and bolt it down you fill the gap with some thin layers of brass sheet called "brass shim" which you cut out to the size required with a pair of scissors.
You have thus "shimmed it up" and bolt it up so it does not wobble, you have shimmed the parts and removed the play, i think you know what i mean.

It may not be easy to buy washers this size but even a tin or aluminium can could be cut to size with scissors and the edges straightened with a hammer to match the gap you want to fill between the frame and the needle bearing collar, no one can see it so it does not have to be pretty.

How much grease was in the needle bearing and on the shaft?

I put a layer of black electrical tape around the square bit of the swingarm on mine, it had started to rust where little chips of paint flaked off because road chips hit this surface and now the tape protects it better.

We are learning a lot from your video, thanks for all the work.