Well, I would worry... It's not an sheering force exclusively... Even if the spools are tight against the surface, they can slide along it, so there is still a constant force on the threads, the upper one being pushed in, the lower being pulled out by the bolt that is able to pivot very slightly... And on a rather thin piece of aluminium, that's enough... In the battle between aluminium threads, and steel bolt, the winner will always be the bolt... It might take a while, but in the end you will end up with the hole being enlarged, fatigued, and in the end either cracked or the threads outright ripped out by the bolt...

A rivnut means you add a set of threads, in either steel, which is best, or in aluminium which works as well... Those threads are supported by a ring of material on either side of the original swingarm walls, that take up the loads a lot better, being nearly three times the width in total... As long as you countersink the spool so it contacts the swingarm, and can't bend, changing the equation, you have a lot stronger threads this way... The threads in them selves are longer by far, probably around 10-15 mm instead of 2-3 mm... The wall/ring around them are three times thicker, and if you select steel rivnuts, a both the ring and threads are a lot more sturdy...

It wouldn't really be much of a problem for you to enlarge that hole slightly, and stick a rivnut in there... I really think it's worth the effort to not have a hole in your swingarm, and the bike on the ground...

 

Markus, did you see my above post #15? Or are U just adding footnotes to it?

BTW, I'm FINALLY getting around to my VR-R & HL circuit redo. Spring is not quite around the corner...

 

IMO, drilling a hole, then adding a riv-nut is even worse than just drilling and tapping a hole. The riv not add pressure to the hole, and is trying to induce a crack by the simple means of being in there.

A proper weld will have no issues with adding cracks. The worst it will do is have the weld crack. If you use a Mig welder with aluminum wire, you will probably have a problem. If you use a Heli-arc(Tig), and you actually know how to properly use it, you will have no problems, and the two pieces will be permanently joined together. My older brother is a welder, and very well respected in his suplemental career. I know enough about welding to know that I shouldn't, even though I can make a weld look good, I'd rather have him do it.

Payh attention to my screen name, and the names in the video. Both of these cars are built by my brother. His previous car held records in the last class he was in.

PSCA Drag Racing with Team Modular Mustang Racing and Garrett Turbo - YouTube

 

Read it, and was adding the why, as to why a rivnut was better than just drilling and tapping thread...

 

I agree that welding is a better option if done by a competent welder with the right equipment...

BUT... And this is a rather big one... You are 100% wrong on the statement on the rivnut... With that simple statement you have made it abundantly clear that you haven't grasped the fundamental behaviour of forces, and how a rivnut works...

You say the rivnut is trying to add a crack by simply being in there... ????

OK, let's take the way you formulated that and step it back a little, to what your actual point was... You mean that the way the rivnut is designed, it adds pressure to the material, going outwards from the hole?

Nope... The rivnut is made of a hollow tube... The tube is thicker in both ends, one end where the outer ring is, one end where the threads are... The middle part is thinner... The result is that the thinner material once riveted crowns out inside the original material, forming the other end... It does not add any pressure outwards in the hole, or very, very minimal, since the thicker material in the ends isn't crowning... If it did, the threads would become deformed, and the rivnut wouldn't work... In fact the force keeping the rivnut from slipping in the hole is the clamping force applied from the sides, not the growth of the tube...

In terms of how forces are applied to the material, the rivnut is a little better than a bolt with washers and a nut on the other side, a little worse than a true rivet... And both are actually better, material wise than a weld... And all three are infinitely better than a short thread with leverage in a thin material...

An improper weld, will however potentially weaken the material, to the point where a cracked weld is the least of your problems... You could end up with a nice hole where the bung and weld where ripped of the weakened material...

However, the reason a weld is still preferable, if done properly is that a welded on bung for the thread will be under the swingarm, so the distribution of forces and where they are applied, are a lot better than when applied like this, in this position... That applies to either rivnut, bolt/washer/nut or simple threaded material...

It's fine to prefer one or the other... But if you are going to advocate one, use facts, not bullshit... It's too easy to point holes in that...

 

Markus, as I stated, I thought you were following up for me.

I don't know how you have patience to respond sometimes. In my old age, it's hard for me.

As I'm sure you also know but many member may not, one major factor when welding, especially aluminum (and given an experienced welder who is certified for the equipment and position to be used) is not knowing the grade (Type) of material and its "condition". There are some filler rods that work well on a variety of aluminum types but very often cast and forged and even extruded shapes have been "heat treated" or are alloyed to "age" into a "condition" (i.e., 6061-T6). So the dire results and foibles you mentioned regarding welding can have several causes.

Bottom line, for most people, a rivnut is simple, inexpensive, effective and expedient for this application compared to welding.