Trunk mounting bolts always break… how to fix?

Hello fello GRiSO peeps!

I have a 2013 1200 with an aluminum trunk by Givi, 30 liters (doesn’t even fit my helmet). The mounting bracket consists of two cross bolts and two under seat bolts that mount to the subframe. The bolts at the bottom of the subframe always break, one of the bolts, and eventually the second.

I do not overload the trunk, in fact it it is empty for most of the time. I do ride in NYC, and somewhat aggressively, but why are my bolts always breaking and how to address?

Is the trunk case so cantilevered that it simply can’t hold much weight?

Has anyone else had this issue?

Is there any way to make the mounting stronger? More bolt locations? Drill out for a larger bolt? I have been using the highest strength 8mm bolts I can find from McMaster Carr…

Should I switch to side cases (good bye lane splitting!)?

What is the best luggage situation on a 2013 GRiSO?

Thanks,
R.

Pix please

Hey! I uploaded… do you see the pics?

[You must be registered and logged in to see this link.]

whyrichard wrote:

Hey! I uploaded… do you see the pics?

no -
when you post there is an icon on the top bar with a floppy disc on top of a picture - that allows you to host a picture

Jon

Can you click on the links in my reply above?

Thanks,
Richard

Ok can see them now - not sure why i could not before lol

The ventura and C-Bow luggage system use the large (8mm?) mounting points that the original luggage bobbins are mounted on.  I have marked them in blue on one picture and left them clear in the other
[You must be registered and logged in to see this image.]

The allen screws further back are 5mm or 6mm and originally just for holding the plastic rear mudguard so if you are mounting to those i am not surprised that they break.

Can you mount it to the 8mm bolt points?

The Givi trunk rack is mounted to the 8mm mounting points, only 2 of them instead of the 4...

whyrichard wrote:

The Givi trunk rack is mounted to the 8mm mounting points, only 2 of them instead of the 4...

so it uses two of those bolts and the side mountings. That may well be the root problem as when the side bolts slacken the rack will pivot on them putting most of the load on those two 8mms underneath.

All i can suggest is put the longest 8mm bolts you can fit into those vertical holes to use all of the thread. Then loctite and torque up all of the mounting screws (at the carrier end as welll) so that the whole thing acts as one rigid load and cannot pivot around the top screws

My wrenching skills are ... erm ... suboptimal ... compared to others here, but I would not have thought that increased rigidity is the answer.

While I have had the Norge's top case crack at the mounting points, cheap plastic, and over-torquing were the cause there.  I solved that with JB on the plastic and large fender washers on the inside to distribute the contact pressure better.

In your case, I would think that higher-grade fasteners -- see, e.g., [You must be registered and logged in to see this link.] at, perhaps,  https://www.mcmaster.com/screws/system-of-measurement~metric/fastener-strength-grade-class~class-8-8/ or higher, might be the answer or, at least, help.

I would also give rubber grommets, washers, or something of that sort a try to cushion the trunk on the rack.  Possibly something like these?  https://www.mcmaster.com/standard-washers/material~rubber/abrasion-resistant-cushioning-washers-6/

Back to getting ready for company here.  Happily for me, it's one of Kathi's all-girl-grade-school-through-college classmates.  As soon as we welcome her, I pretty much get three days to myself in the Moto Grappa with the GRiSO and its friends.  

Bill

That rack design is sub optimal. All the force is applied to the two screws underneath. I'd be getting a second set of brackets made to help spread the load.

Crude drawing:


[You must be registered and logged in to see this image.]

Looks like there's a massive lever effect plus oscillating up & down a lot as you ride, must put lot of fatigue stress on the bolt (not helped if the plastic undershield is sandwiched in as it gives extra wiggle room). I have same problem with bicycle saddle bolts breaking regularly if I push saddle back making bit more leverage from by butt. Electroplated Low-medium grade 8.8 tensile bolts are worst for this & switch to higher (12.9) tensile strength and no plating may help (yes it will rust, but hey ho)....don't over or under tighten it !

Interesting as it looks similar to my Hepco mounts other than they have a small tube welded onto the end to not put pressure on one spot on the bolt, and I have DEFINITELY overloaded mine and ridden on rough roads. I wonder if that might improve it, if you could have someone weld up a slight change in design.