I have the standard luggage rack from Yamaha, so if you have something else, it's likely different. There are 3 screws holding the luggage rack on and I removed the two rear ones. These are M8 x 110mm long. These can't be reused as once the case is in place, there isn't enough length to reach the threads. I found some 130mm long on Amazon and that was perfect.
https://smile.amazon.com/dp/B01FYBY4EW?psc=1&ref=ppx_yo2ov_dt_b_product_details
There is a gap between the case and the rack which I measured to be 0.506", so I found some spacers, also on Amazon.
https://smile.amazon.com/dp/B09DK4WSS7?psc=1&ref=ppx_yo2ov_dt_b_product_details
For good measure, I placed some rubber washers under the case. They came from this Harbor freight kit.
https://www.harborfreight.com/141-piece-washer-seal-assortment-67552.html
I also added two more screws further back. There are two holes in the luggage rack that I used. These are M8x25mm button head screws with flat washers, lock washers and hex nuts. I had some in the garage, so I didn't have to buy any.
I didn't take photos when did this, but here's the process:
Place the case on the bike and determine where you want it. I had my wife sit on the passenger seat to be sure I was leaving enough room for her. Remove the case and luggage rack. With the case upside down and the luggage rack on top, mark and drill (4) 5/16" holes using the luggage rack as a guide.
Re-install the luggage rack but only using the front stock screw. Make sure the rear holes line up and tighten the front screw. You won't be able to get to that one once the case is in place.
Now comes the fiddly part. Place (2) of the 1/2" spacers on the luggage rack centered on the forward set of holes. Place the stock washers on the new 130mm long screws and insert them through the corresponding holes in the case. Place two rubber washers on the screws on the bottom side and while holding them in place get the case in place the get the screws through the spacers and the threads started. Only give them a couple turns at this point because you still want to move it around.
The rear screws have a flat washer inside the case, a rubber washer under the case and then a flat washer, lock washer and nut on the bottom. Tighten everything up.
I will probably change a couple things to make things easier and stronger. I will probably glue the rubber washers to the case with some silicone. This will make is less fiddly to install. I would like the washers inside the case to be larger, to spread out the load on the case a bit. I am thinking 5/16" fender washers or maybe an aluminum plate that would go under all 4 screws. We will see...
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