Making Special Bolt

[ErichKeane]

I thought of trying that too, Erich. I only found one picture and the break was at the longer threaded end that would go thru a saddle bag and have a nut threaded on.

Perhaps removing the hex portion would help too, having the saddle bags clamped more directly to that shoulder would better transfer weight.

Alternatively, could you increase the diameter of the longer thread? Any amount that gets any bigger vastly improves its strength.

 

[rgray]

Might be as simple as installing a tight piece of fuel line over the extended part of the bolt.
Or putting an o-ring or rubber washer under the sort end.
Getting rid of the tuning fork effect is my thought.
And that could be way off as I'm not familiar with the bike and mountings.

 

[mikey]

Looks to me that the single attachment point at the bottom of the U-shaped bracket is insufficient to stabilize that saddle bag, allowing it to vibrate and weaken the bolts over time. Could you broaden the contact point of the bottom mount?

 

[Splat]

Perhaps removing the hex portion would help too, having the saddle bags clamped more directly to that shoulder would better transfer weight.

Alternatively, could you increase the diameter of the longer thread? Any amount that gets any bigger vastly improves its strength.

Can't increase the diameter because that threaded end must go thru the back rest mount and saddle bag mount. Removing the hex portion and adding flats onto the spacer is an idea I was going to try. The way the whole thing goes together is:

(1) special bolt screws into bike frame (Loctite applied)
(2) back rest mounting arms
(3) saddle bag mount
(4) saddle bag
(5) fender washer, lock washer, nut

 

[Splat]

Looks to me that the single attachment point at the bottom of the U-shaped bracket is insufficient to stabilize that saddle bag, allowing it to vibrate and weaken the bolts over time. Could you broaden the contact point of the bottom mount?

Well, that's another thing I was thinking about. I was figuring how to weld a strut to the bottom of that saddle bag bracket and have other end mount to maybe the rear passenger footpeg bolt or somewhere else.

 

[markba633csi]

Everything vibrates on a motorcycle; I'm not surprised it's breaking. It's a hostile environment for fasteners. If you can't upsize the diameter then I would use an alloy steel or stainless

 

[mikey]

Well, that's another thing I was thinking about. I was figuring how to weld a strut to the bottom of that saddle bag bracket and have other end mount to maybe the rear passenger footpeg bolt or somewhere else.

I think anything that keeps the bracket from moving will prolong the life of the two bolts up top. It isn't that they aren't big or strong enough; its metal fatigue from constant bending.

 

[hman]

Assuming it's metal fatigue, there's one thing you might want to look at ... check the transitions between the larger diameter sections and the "basic" bolt diameter. Sharp corners become stress risers. If you fabricate your own, add a small radius to each transition.

 

[homebrewed]

I add another vote for radiusing the transitions, if the rest of the hardware permits that (if not, perhaps the other pieces need to be modified). Another thought that occurs to me is that the dynamic loading (due to vibration) will increase the peak stress on the bolts.

Where do these bolts fail? That would provide some clues on what needs to be beefed up.

 

[Splat]

Assuming it's metal fatigue, there's one thing you might want to look at ... check the transitions between the larger diameter sections and the "basic" bolt diameter. Sharp corners become stress risers. If you fabricate your own, add a small radius to each transition.

Yep, I agree. That was the second thing I thought about...the first being bolt length vs weight. I'm going to also not have that nut looking piece on there. I can make a few flats on the spacer which should be good enough to tighten everything down. That'll make the total length shorter, too, which should be good. Hopefully this weekend I'll have a try at making one.