Rear wheel finally swapped.

[X-Ray]

I read that about the GSX600F caliper mount as well Tony, thinking I may still look into that for the '93, as I myself am not totally happy with the footpeg bolt arrangement we have for the torque arm presently. Before the '93 makes the trip to Dartmouth in March, I will hopefully have something different in place.

Gavin, that custom made caliper bracket looks great, from the look of your photo you have welded that onto the swingarm?

[Millietant]

All this makes me happy I opted for the 5" x 17" Thundercat wheel swap option - used the original caliper and torque arm - only needed to machine 8mm off the caliper mount bracket to get the wheel aligned.......verrrry simple !!

[scotiafj]

Hi yeah that was Me that used the rear caliper from a 88 GSX600F , I used it because the bolt that went thru the footrest that held the underslung gsxr caliper torque arm kept breaking ,the last time was when I was at a bike rally and had to use some wire to hold the torque arm in place , and rode home on the sunday after the rally only using the front brakes, it was 120miles from home so I took it easy , anyhoo I used the underslung caliper mount spun round so it was @ the top and sourced a gsx600f caliper and bolted it onto the mount I used a rose jointed arm that I had lying about that jus needed a few turns on the eyes to line up with the FJ caliper mounts which are on the swing arm,Ive done about 3000 miles since fitting the caliper and have had no issues at all,I was so paranoid about the bolt snapping again that at one point I was gonna refit the fj caliper and 16'' wheel back on it was getting no fun riding the bike and wondering if the nxt time I braked the bolt would snap and lock up the wheel or worse ..glad I didnt and fitted the gsx600f caliper n kept the 17'' rear wheel..things is now Ive been thinking of fitting a thunderace rear wheel and caliper

[fj-f3a]

Gavin, that custom made caliper bracket looks great, from the look of your photo you have welded that onto the swingarm?

The mount is manufactured from 6061T6 Aluminium. It is held in by the axle. No Welding. The lip shown in the top photo sits on the top of the swingarm and stops the caliper from rotating.
This caliper is from an XJR1300 and it is fantastic.

If possible, could someone post a photo of the GSXR caliper and mount by themselves.
There must be an easy solution to the mounting problems.

[MACHV]

Hi yeah that was Me that used the rear caliper from a 88 GSX600F , I used it because the bolt that went thru the footrest that held the underslung gsxr caliper torque arm kept breaking ,the last time was when I was at a bike rally and had to use some wire to hold the torque arm in place , and rode home on the sunday after the rally only using the front brakes, it was 120miles from home so I took it easy , anyhoo I used the underslung caliper mount spun round so it was @ the top and sourced a gsx600f caliper and bolted it onto the mount I used a rose jointed arm that I had lying about that jus needed a few turns on the eyes to line up with the FJ caliper mounts which are on the swing arm,Ive done about 3000 miles since fitting the caliper and have had no issues at all,I was so paranoid about the bolt snapping again that at one point I was gonna refit the fj caliper and 16'' wheel back on it was getting no fun riding the bike and wondering if the nxt time I braked the bolt would snap and lock up the wheel or worse ..glad I didnt and fitted the gsx600f caliper n kept the 17'' rear wheel..things is now Ive been thinking of fitting a thunderace rear wheel and caliper

Were any of these broken bolts a 12.9 class?

[FJmonkey]

Here is what I did on my GSXR rear swap. I made a simple bracket out of stainless steel. I got all the bits assembled on the bike to see the correct position to mount the bracket and marked the positions. Then drilled the 2 holes and used riv-nuts. Many thousands of miles with no issues.

[Tuned forks]

Out of curiosity Monkey, are those unhardened stainless steel allen head bolts?  I've experienced a lot of soft SS hardware.  Did you also use Loctite or anti-seize?

Joe

[scotiafj]

Hi yeah that was Me that used the rear caliper from a 88 GSX600F , I used it because the bolt that went thru the footrest that held the underslung gsxr caliper torque arm kept breaking ,the last time was when I was at a bike rally and had to use some wire to hold the torque arm in place , and rode home on the sunday after the rally only using the front brakes, it was 120miles from home so I took it easy , anyhoo I used the underslung caliper mount spun round so it was @ the top and sourced a gsx600f caliper and bolted it onto the mount I used a rose jointed arm that I had lying about that jus needed a few turns on the eyes to line up with the FJ caliper mounts which are on the swing arm,Ive done about 3000 miles since fitting the caliper and have had no issues at all,I was so paranoid about the bolt snapping again that at one point I was gonna refit the fj caliper and 16'' wheel back on it was getting no fun riding the bike and wondering if the nxt time I braked the bolt would snap and lock up the wheel or worse ..glad I didnt and fitted the gsx600f caliper n kept the 17'' rear wheel..things is now Ive been thinking of fitting a thunderace rear wheel and caliper

Were any of these broken bolts a 12.9 class?

Yes they were 12.9

[X-Ray]

I just ordered an '88 GSX600F rear caliper from ebay to try on the '93. If it mounts up ok and gives some more feel/bite than the weak GSRX caliper currently fitted, it will be a win. 

[MACHV]

Here is what I did on my GSXR rear swap. I made a simple bracket out of stainless steel. I got all the bits assembled on the bike to see the correct position to mount the bracket and marked the positions. Then drilled the 2 holes and used riv-nuts. Many thousands of miles with no issues.

Excellent solution. I just wrestled this whole thing back together though. I need some serious mental downtime before I pull it all back apart to do this though.

[FJmonkey]

Out of curiosity Monkey, are those unhardened stainless steel allen head bolts?  I've experienced a lot of soft SS hardware.  Did you also use Loctite or anti-seize?

Joe

Joe, I did not get any special hardness so I really don't know. The bolts are in shear and will have way more strength that the torque arm can put on it. I did use a medium strength thread lock.

[Bill_Rockoff]

Here is what I did on my GSXR rear swap. I made a simple bracket out of stainless steel. I got all the bits assembled on the bike to see the correct position to mount the bracket and marked the positions. Then drilled the 2 holes and used riv-nuts. Many thousands of miles with no issues.

Did you drill those holes in the bottom of the swingarm, in the horizontal element on the bottom?

Got any photos of how it looks now, after the many thousands of miles?

I notice that the stock swingarm has all the fiddly little bits welded onto the outside of the swingarm extrusion. The only exception I can find is the factory bracket on top of the RH side, which is held in by a small screw threaded into the top about halfway between the rear axle and the lower shock mount. Being on top, this screw is under compression radially; the force of the bike's weight on the rear wheel is trying to bend the swingarm up in back, which tries to smoosh the front and back of that bolt's threads together toward each other. You can do this on things that are in compression, because the aluminum from the swingarm would press in toward the center of the bolt and try to squish the bolt. If this screw were on the bottom, this hole would be in tension, and holes make your stuff weaker in tension even if you fill them with other stuff.

What worries me a bit about your assembly is that you have drilled holes into the aluminum on the bottom, where it is under tension. Drilled holes filled with hardware are okay under compression, but they are not okay under tension; you have effectively reduced the cross section of that horizontal bit by the width of your hole. A 1" wide section of flat-stock under tension with a 1/4" wide hole drilled in it will basically be a 3/4" wide section of flat-stock under tension.

Not only have you done that, but it looks like have drilled two holes offset from each other. If you have a 1" section of flat stock in tension and you drill a pair of 1/4" holes, you really don't want them offset from each other, you want them lined up so that they both only effect the same 1/4" of width; if you offset them so they don't overlap at all along the axis of the stress, you effectively turn your 1" section of flat stock into a 1/2" section of flat stock.

And also, you have drilled those holes in the front part of the swingarm, between the frame mount and the lower shock mount, which is the more-heavily-loaded section of a swingarm on a bike with a monoshock setup like the FJ's. This would be hardly a problem at all on a traditional two-shock suspension, where the shock bottoms mount near the axle, but it is a much bigger deal on a swingarm like the FJ's where the shock mounts between the swingarm pivot and the axle. (Since the distance from the lower shock mount to the swingarm pivot is about 1/3 as far as the distance from the lower shock mount to the axle, the part where your holes are is under about 3 times the stress that they'd be on the back part of the swingarm.)

So what all this means is that you have made your bottom horizontal member of your swingarm effectively smaller in cross-section, by the widths of your holes, in the exact part of your swingarm that should be the most effective at keeping it from bending, in the front part of your swingarm that is subject to the highest bending forces. You have basically turned your box-section swingarm into a c-channel-section swingarm, with the open end of the "c" facing down.

I mean, it *could* be fine. But you will definitely want to inspect it visually periodically. You will be looking for evidence that those holes are becoming elongated, or that the sides of the swingarm are buckling.



And if I were you, I would think about sourcing another swingarm (like $45 on ebay?) and taking another pass at your design, maybe either welding a torque arm bracket onto the bottom, or fabbing a completely separate bracket that clamps on around the box swingarm assembly, rather than drilling holes in the part where holes are the most disruptive.

Because you do NOT want to make holes in the bottom of a box-section swingarm. You want the top and bottom elements of a box-section swingarm to be intact, where they can resist the bending load by being in compression and tension respectively. If HAVE to make holes in an assembly like that, you want to make them as close as possible  to the center of bending moment. It's like how you want to drill a hole through the center of a floor joist rather than notch the bottom. (If you drill a 1" hole in the center of a 2x8, it's basically just as strong. If you cut an inch out of the bottom, you have basically made a 2x7.)

___
|   |
|   |
|   |<- you really want to make holes here
|   |
|__|<- and not here.

Meanwhile, definitely check it often.

[Bill_Rockoff]

Too late to edit:
___
|   |
|   |
|   |<- you really want to make holes here
|   |
|__|<- and not here
  ^
and DEFINITELY
not here.

[ribbert]

.........I notice that the stock swingarm has all the fiddly little bits welded onto the outside of the swingarm extrusion.....

Bill, you understand the forces at play and I agree with every single thing you said - technically! 
However, in practice I doubt the holes would compromise the integrity of the arm in operation. Having said that though, I would be reluctant to do it for other reasons.

I would have a greater concern about the rivnuts in aluminium, I would worry the holes would elongate over time, a process that would speed up exponentially as the play increased. It is the sort of thing I might do on my own bike and monitor but not on someone else's.

I would also want a thicker bracket to minimise the shearing risk by spreading the load over more over more of the bolt, especially the one the arm attaches to.

But hey, Mark may just be a better engineer than both of us. If his shows no sign of wear in the above mentioned areas, it's doing all it needs to do.

If someone were to ask my advice on this topic I would simply say "just weld a tab where it needs to go on the arm and move on to the next job, there's nothing to think about". If your skills or enthusiasm only run to finding some other bolt hole somewhere because it's easy, maybe you shouldn't be friggin' around with your brakes.

Someone in this thread suggested welding was no longer an option as the only welder he knew recently died - find another one, they're hardly rare.

Noel

[Bill_Rockoff]

I doubt the holes would compromise the integrity of the arm in operation.

Those holes are on the bottom of the swingarm. When the swingarm is loaded by a rear wheel holding the bike up plus the shock mount pressing down in the middle, the bottom of the swingarm is in tension. A piece that is in tension is acting like a bunch of strings being pulled tight. Drilling a hole in that part is like cutting some of the strings. All the other "strings" have to take up the load. Putting something like a bolt back in the middle is like putting a bolt back in between the cut ends of your strings - it doesn't help at all.

So your doubt is completely unfounded. Drilling holes in a part that's in tension absolutely would compromise its integrity.

Drilling the holes in the top (like the factory hydraulic hose bracket mounting screw) would have been better, because the top of the swingarm is in compression. Material in compression doesn't act like strings, it acts like a bunch of blocks pressed together. You can drill out some of the aluminum in the middle and replace it with a threaded bolt, and it would be fine in compression. So, one more reason why mounting the caliper on top might be a better solution - you would have the caliper's torque arm on top in compression, mounted to the top of the swingarm in that is also in compression. (Now, if you just drilled a hole and didn't thread a bolt in there, it *would* be weaker in compression.)

I would also want a thicker bracket to minimise the shearing risk by spreading the load over more over more of the bolt, especially the one the arm attaches to.

I think the shear force occurs at the interface between the two parts, which is not affected by their thicknesses.  The bolt is the strongest of the materials there; I don't think his mounting plate is going to scythe through the bolt and sever it. And I don't think the shear stress is affected by the thickness of the two elements applying the shear.

Then again, I took that class 35 years ago and I think I got a "C" in it.

Also, as long as it's bolted correctly, there shouldn't be any movement or elongation from forces applied from the torque arm mounting plate. The bolts clamp the plate to the swingarm, and your force is ideally resolved in the friction between the plate and the swingarm which keeps the two parts from moving relative to one another. You aren't depending on the bolt's resistance to shear to prevent movement, you are depending on friction between the two parts. The bolt should be in tension. Otherwise, you're not bolting it tight enough.

But hey, Mark may just be a better engineer than both of us.

It's pretty likely that both of you earned better grades in engineering school than I did. Also, my area of practice is not structural. But most of my observations here are based not so much on my expertise, as on the idea that "the people who had the expertise(*) aren't doing it that way, there are probably reasons for that." Kind of like how, structurally, "open-web steel joists" are a thing, but "serrated-edge beams" are absolutely not a thing, because cutting the tops and bottoms will make it weaker in bending.

(*)There's nothing wrong with reevaluating someone's expertise, but it helps to understand why they made their design choices before you second-guess them. To paraphrase a guy on a car forum I'm on, "there's nothing wrong with reinventing the wheel, but you have to understand the concept of 'round' first."