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Discussion Starter · #1 · (Edited)
This is not an easy swap, however it is possible and the results are very nice.
my bike is a non ABS gen1. I can't know if any other bike would have additional clearance issues.
One of the first annoyances I had with the gen 1 FJR was the inability to dial in a proper rider sag. or to fine tune compression damping and of course the saggy stock spring.
An internet search of shocks with appropriate spring rates, compression and rebound damping, and a similar length found the hayabusa shocks. all years are 130mm long (the FJR shock is 125mm)
this, for me, provided the added benefit of raising the rear which makes the steering a tad quicker, but not so much that I can't still use the center stand. as a matter of fact, with new tires front and back, the rear tire still clears the ground by 1/4"
the gen 1 bussa shock has a 131 n/m spring. the gen 2 bussa shock sports a slightly stiffer 145 N/M spring.

So what is required.
On my non-ABS gen1 there is a plastic storage compartment under the riders seat. Under that is what appears to be another small storage container. it is part of the under tail plastic, but, forward of the flap that keeps the shock clean.
I had to cut a section of this plastic to clear the remote reservoir of the new shock about the full width of the small box shape and about 1/2 the length and 1/2 the depth. I did this with a whole saw and a sawzall. the results were fast and easy but since you can't see it I wasn't too woried about a clean cut.
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the next step involved the unusually wide upper mount. my first thought was to add spacers to either side of the upper shock mount but decided to just press out my OEM upper shock mount, grind down the OD to fit the busa shock and press it into the bussa upper shock mount. centering it perfectly in the shock. this was by far the most dificult and time consuming part. lastly i drilled the lower shock mount to 12mm and bought a 12mm bolt from tractor suply. the 80mm M12 1.75 had an un-threaded shank of just the right length. a M12 1.75 nylon lock nut, also from tractor supply was also used. before installing the shock i installed the new bolt and nut on the lower mount and leaving just a couple of threads past the lock nut cut the excess threaded portion of the bolt off.
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after installation I set my race sag (also called dynamic or laden sag) to 35 mm and had 11mm of static or unladen sag. this indicates a good spring rate (static sag approximately 1/3 of race sag) too low of a spring rate will require more preload to achieve a good race sag, which reduces static sag. as a 230 lb rider, my preload was minimal with only 5 threads showing above the spring.
I started with the sport rider recommended damping setting for the 2018 Hayabusa, but ultimately settled on 12 clicks out (out of 24) on the compression damping and 9 clicks out (out of 24) on the rebound damping.

this is obviously much more involved than buying an aftermarket shock and bolting it in, however the final result is a very well planted, firm rear suspension, with a good spring rate and almost an inch more travel than the factory shock, for only $100. but does require more than basic hand tools. you will need a press, a set of calipers (for precision measurements) a drill press with 12mm bit and a bench grinder at the minimum. I also used a drill with whole saw, sawzall, and a grinder with a cutting disc.
 

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Discussion Starter · #3 ·
This.
Is.
Fucking.
Wild.

I love it.

This is "Red-neck-ery" of the highest caliber and I highly approve.
View attachment 88365
Thanks 😊
back in the early 90s I was an old school hot roddder. Which meant, rather than ordering new performances parts for our cars, we scoured junk yards for parts from other cars, that could be made to fit ours for a performance upgrade. This always involved a lot more work, some creative re-engineering and no guarantees of success, but I always found it a lot more satisfying when it worked out. Being able to research specs on the internet and having parts delivered to the house has made this easier. Most shock swaps are a lot less involved than the FJR with its unusual top mount.
 

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Most folks would have just bolted on a Gen 3 stock FJR shock. That is some outside the box thinking.
 

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Discussion Starter · #5 ·
Most folks would have just bolted on a Gen 3 stock FJR shock. That is some outside the box thinking.
I looked at that, but, really wanted to be able to set my sag and that requires a preload adjustment. Independent compression and rebound adjustments are nice too.
Despite the fact that I ride a lot slower than I did in younger days, I still want to dial in my suspension as close as I can.
 

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Nice. I had a Gen 2 FZ1 and there was a guy selling an adapter for the shock that allowed a fully adjustable shock from an R1 to me mounted. Quite the upgrade.
 

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Nice. I had a Gen 2 FZ1 and there was a guy selling an adapter for the shock that allowed a fully adjustable shock from an R1 to me mounted. Quite the upgrade.
I've got a similar thing on my Gen 1 FZ1. Guy makes a couple small mods to R6R shocks and provides new dog bones so it all bolts in.
 

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Discussion Starter · #9 ·
I've got a similar thing on my Gen 1 FZ1. Guy makes a couple small mods to R6R shocks and provides new dog bones so it all bolts in.
I liked the S1000rr shock for my gen1 FZ1
That one was the propper length so you didn't have to monkey with the rising rate geometry by changing dogbone length (shorter dogbones mean less shock travel for a given wheel travel) and as an added bonus had both high and low speed compression damping.
 

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Discussion Starter · #10 · (Edited)
I think racetech.com under rated the spring rate for the gen2 bussa shock. So, at this time, actual spring rate of the gen2 bussa shock remains unknown.

1st reason for suspecting a higher than advertised spring rate. This spring provides a surprisingly firm ride for a 230lb rider. Even 2 up , with soft damping settings, and a combined wait of 400lbs without gear, I never used the full shock travel, even on rough SC roads.

2nd reason. As an experiment I swaped a spring from a gen 1 busa shock onto my gen 2 shock, it has the same Uninstaller free length and should only be 10% softer, however, obtaining the same sag went from nearly no preload to 100% of it, with a noticeably softer ride

3rd reason. Look at this picture comparing my YSS shock I tried previously with the gen 2 bussa shock. Notice the difference in spring thickness at what should be nearly the same spring rate.
140 n/m to 14.5 kg/mm.
these are just my observations. do with this information what you please.
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