Rear fender swingarm mounting

thrillseeker

Been Around the Block
I've been doing a little contemplating on how I'd mount a rear fender to the swingarm of my CB360 and so far I've decided on a design that seems like it should work. I'm using a fiberglass fender so the mount doesn't need to support much weight. But I do understand that it will be subject to a lot of stress from bumps and vibration. I came up with a rudimentary sketch and would like some input.

I'm planning on using 1/8" steel. The mount will fasten to the swingarm with 4 bolts. The fender will attach to the bracket with 3 staggered bolts. Two towards the bottom and one closer to the top. The fender is about 10" long. I'm hoping to mount it so it hugs the tire. Maybe sitting an inch off the tire. But if that's not a good idea I'm okay with moving it forward a little more

Does this seem sturdy enough?
Is it bad to put holes/bolts through the swingarm?
Should I weld it to the swingarm instead?
Is the diagonal brace on the bracket needed?
Is it okay to extend out close to the tire like I have it?
Any other suggestions?

Thanks all.

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I hope everyone enjoys my artwork. It may be worth big bucks in the future
 
Seems like it should work. You could always go for 4 bolts through the fender. Have two "upper" fasteners on either side of your gusset. Having them staggered like that is a good idea.
 
Thanks guys! 1" was an estimate. I just want it fairly close but not too close that it rubs from flexing. It will have bolts/nuts sticking out so it can't go too close. Unless I jb weld it instead. Ha. I like your design Kanticoy. I may have to modify my design to be somewhat similar.


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Okay I think I have something I'm pretty happy with now. I think I'll just make the mounting tabs a little wider to give it more stability. I like this design a lot better than my original design. Thanks Kanticoy!

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I had a helper too

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Use button head allen bolts from the tire side for a smooth look and most clearance. I had clearance issue with the fender mount bolts on the legs being too wide(or is the tire too wide?) to fit the tire in easily,button heads gave me the clearance I needed and while still tight it is easier to push the tire past the smooth heads than if they were sharp edged bolts.
 
thrillseeker said:
Thanks guys! 1" was an estimate. I just want it fairly close but not too close that it rubs from flexing. It will have bolts/nuts sticking out so it can't go too close.

I'd go for alloy rivets to through the fender then the bracket, keep the mass down and only a couple mm protrusion.
 
both good suggestions. thanks guys. I do like the idea of rivets. I dont have a rivet gun but this would be a good excuse to get one. I think I'll also make slots in the bottom plate so the fender can be adjusted as needed. I also realized I need to make sure the tire is straight to determine placement of the bracket. So I may want to wait until the front end is together before I actually drill holes in my swingarm!

Now to find someone with a tool that can cut 1/8" plate steel. I wonder if anyone near me has a metal cutting band saw. hmmm...
 
True, I guess I could use a coping saw for the curved piece. +1 on the loctite.


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First, you may want to consider making your fender longer. It depends on how functional you want it to be. Flak from the rear tire does not fly straight away from the center, but also gets thrown from a tangent due to the tires surface speed. So you can count on anything above the long arrow in my pic to be unshielded by the fender.

I'm guessing that you do not intend to add struts - the longer the fender the more you will need them. They solve several problems. With the single mount, the mount has to keep the entire fender from flexing under impact with bumps as well as being stiff enough to not flex itself. This is easy with steel but very heavy, challenging out of aluminum due to fatigue problems. with struts, you could make the fender longer, lighter overall with a very tiny lower mount made of steel more like your original drawing. Two small bolts on the swing arm and two on the fender. very strong, very stiff, very functional and no problems.

Regardless, a good way to attach your fender to your brackets is to make an 1/8" curved plate to conform to the curve of the fender to mount inside the fender on the tire side. Through bolt it to your outside mount to a pair of horizontal bolts by threading the plate itself. Assemble everything off the bike and cut the bolts almost flush on the tire side. This way you have a very easy to assemble bracket assembly and you can use the attractive button head bolts on the outside with a split lock washer under the head. The inside plate can not turn with two bolts in it, will be invisible, offer vastly better and more friendly clamping force on the fender, and be easy to assemble on the bike with no fiddly bits inside where it is hard to reach. Always use the Loktite!
 

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