81 GS650G - what were these bolt holes on the frame used for?

[seinwave]

I have started moving again on a long-stalled project involving a frame mounted fairing on my bike. I've been hemming and hawing and drafting various weird bent-metal mounting solutions for quite a while, somehow without realizing there are two threaded bolt holes (seem to be about M10 or M12) on a cross-beam member just under the headstock. These are ideally positioned for a nice tight vetter-style lower mount.

But what was the original purpose of these mounts? Factory-option oil cooler? Factory-option fairings (or at least easy installation of aftermarket fairings)?

Secondarily... am I going to screw anything up by taking most of an ~8lb vertical load (times a factor of safety for dynamic loads) in shear through these two? I can't imagine I would, but I don't want to find out I'm wrong catastrophically. This isn't some sort of brazed on mount intended for cosmetics or something like that?


(not my bike, I'm away from home so I pulled something off google images. mine is much cheaper - and, dare I say, better - looking).

 

[seinwave]

Not familiar with 650's but horn mounts I think.

That was a thought I had too. However, my bike has the horn mounted up above that on a separate bracket, and from what I can tell from images of other people's bikes, that seems standard. EDIT: I guess it's possible they were intended for aftermarket extra-loud extra-heavy horns, or dual horns, but that seems far more niche than a fairing kit.

 

[Grimly]

Oil cooler mounting holes.

 

[seinwave]

Oil cooler mounting holes.

Thanks for the info. That gives me pause on using these for a fairing mount. An oil cooler probably only weighed about two or three pounds wet, so I'd be gambling a little on how many times the margin of safety Mr. Suzuki put into these threads was...

 

[Grimly]

Thanks for the info. That gives me pause on using these for a fairing mount. An oil cooler probably only weighed about two or three pounds wet, so I'd be gambling a little on how many times the margin of safety Mr. Suzuki put into these threads was...

Well, it depends.
One complete full-length fairing I had was a rectangle of steel bar welded to the front of the headstock. The fairing bracket was held on to that by two 8mm bolts... of course, the bottom of the fairing had other brackets so the entire weight wasn't being taken by the headstock bolts, but plenty was.
Never had the slightest worrry about that fairing, other than it was a bad design that funneled freezing cold air at my knees.

 

[seinwave]

Well, it depends.
One complete full-length fairing I had was a rectangle of steel bar welded to the front of the headstock. The fairing bracket was held on to that by two 8mm bolts... of course, the bottom of the fairing had other brackets so the entire weight wasn't being taken by the headstock bolts, but plenty was.
Never had the slightest worrry about that fairing, other than it was a bad design that funneled freezing cold air at my knees.

Without getting too much in the weeds (I'll probably make a dedicated thread when progress begins again)... what I think you're describing is how the fairing stay (and fairing and headlight) I liberated from ebay for a song is supposed to attach to its bike of origin - a rectangular lug on the headstock. I don't have the skillset, tooling, or desire to weld a piece of steel to my headstock, so I'm having to get creative. Many bikes have enough room to slip a clamp around the headstock, but the 650 is too well-gusseted to allow that.

My current plan is to use the tiny bit of "around" available to put a very slender 5mm u-bolt and some bent adapter pieces to pick up the original headstock mounting points. I will avoid this part picking up major loads - it's mostly to prevent the central stay from vibrating/bouncing against my poor frame, as well as providing a little lateral-linear stability. It'll probably also be okay to take most of the thrust load from drag.

Most of the bending load (weight) is planned to be taken by the bent piece I want to attach to the crossbar I identified in this thread. If you look at old semi-generic Vetter stays, they're basically two pieces of L-shaped angle iron connected by some cross-bars. The L piece goes up the sides of the fork/triple tree and then juts out; the crossbars run transverse and attach the L-beams to the two frame rails (and each other). The piece I'm drafting is essentially that assembly, but made of a cut and bent aluminum sheet (about 1/8") instead of (welded?) steel bar, and supported through the crossbeam bolt holes.

So my plan relies on this piece being supported in single shear through these two bolt holes. The math checks out, but as a trained engineer, I know making sure the math theoretically works is the first step. The second step is to run it by people who know what they're doing so they can poke holes in the plan. If I decide against using these bolt holes, the vetter fairings use souped-up P-clamps to transmit load to the frame, and I think I could go that route too. It's just not as elegant IMO.