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built my own swingarm

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Guest

Guest
I have built a 4" over swingarm for my 80-1100 and am using a 98 Kat 600 wheel 4.5". I am in the process of lining things up. I know it's crucial to have the sprockets aligned but how perfectly centered in the swingarm does the wheel have to be? Can it be out 1/4" or how about 1".
Secondly, I have to use a 1100 rear axle so I need to swap some bearings around. Will the bearings in the Kat wheel just tap out?

Nastyjones
 
The wheel needs to be exactly in line with the front wheel, no misalignment at all. Not sure what that means relative to geometry of the swingarm on your bike - the wheel could appear to be off to one side when fit to the swingarm, but when the wheel/swingarm is installed on the bike it needs to be perfectly in line with the front.
 
Yeah what he said, it has to be dead center with the front wheels line of forward travel otherwise the bike and bars will be cockeyed going down the road straight. The line up of the spockets are actually secondary to the line up of the wheel, you can correct the spockets or live with some misalignment but the whole bike turns to **** if you move the wheel off-center just to perfectly line up the sprockets.
 
Swingarm

Swingarm

I have built a 4" over swingarm for my 80-1100 and am using a 98 Kat 600 wheel 4.5". I am in the process of lining things up. I know it's crucial to have the sprockets aligned
Click to expand...

After discussing this with Katman over several evenings, I think the chain alignment needs to be within 0.125" ; that is 1/2 the difference between 3/8" offset and 5/8" offset

but how perfectly centered in the swingarm does the wheel have to be?
Can it be out 1/4" or how about 1".
Click to expand...

Wheel only needs to be aligned well enough to achieve clearance. Since chain is usually closest to the wheel look there for your constraints. On my GSXR conversion, the Bandit arm does not provide enough clearance for the rear master cylinder. So I moved the swing arm over by 5 mm and adjusted the wheel spacers by an opposite amount to keep the wheel in the same spot relative to the bike.

As Ed said, ultimately it is the wheel alignment to front wheel (and center of the bike) which are important.

Rear wheel centering with respect to the frame should be about +/-0.030" . The reality is there are some big tired Hyabusas that are off by much more than that (inches) and they work but not sure how the handling is affected.

Secondly, I have to use a 1100 rear axle so I need to swap some bearings around. Will the bearings in the Kat wheel just tap out?
Click to expand...

Probably

A note of caution: I hope you are in the process of bracing that arm. It looks extremely prone to flexing. :-k.

Pos
 
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As mentioned, the critical offset is that of the center of the wheel respective to the centerline of the frame. I know that there are bikes out there that have wheels offset to make fitment easier (I would not suggest this) and they seem to run down the road just fine. That being said, line it up perfect and you can ride hands free if you want.

Also, it will GREATLY effect tire wear on the chicken stripes and when in a tight curve, you WILL feel the "hop" over the ridge. This is a feeling that you don't want. Spend the time and effort to do it right. :-\\\ ;)
 
I hadn't planned on bracing the arm. It is 1/4" steel and I just can't see flexing being a problem. As for the rest of the answers, thanks guys, I appreciate it. I will make sure the wheel is centered and then worry about the sprocket. Not sure if the arm will work but I am going to give it a try.
And the bearings? I can just drive them out right?

Paul
 
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I hadn't planned on bracing the arm. It is 1/4" steel and I just can't see flexing being a problem.
Click to expand...

Go look at a modern sport bike and see what the swing arms look like. That should be enough to suggest to why any swing arm flex is bad and why people swap out for stiffer arms and brace arms than the ones you already have.

Given your comment about 1/4" steel, I'm assuming you have never taken a strength in materials class. Enclosed cross-sectional Area has more to do with stiffness than wall thickness. Actually it it is more precisely cross sectional moment of inertia, but I suspect that is not telling you anything.

Don't be surprised if your rear squirms around, in fact look out for it. This should be a learning experience for you; just wear a helmet and jacket.

When you do try and improve your arm, think about what makes an "I" beam stiff under bending moments but weak under torsional moments. It will help.

http://en.wikipedia.org/wiki/I-beam

Pos
 
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If the wall thickness in those tubes is truly 1/4" thick, it should be fine. The stock GS tube swingarms have less cross sectional area and are no where near 1/4" thick, yet they seem to hold up fine.
 
Nessism said:
If the wall thickness in those tubes is truly 1/4" thick, it should be fine. The stock GS tube swingarms have less cross sectional area and are no where near 1/4" thick, yet they seem to hold up fine.
Click to expand...

And they are engineered by real engineers, welded by real welders, and braced appropriately.
 
Ed

Ed

You can hardly compare that swinger to stock. The stock swinger was designed by an mechancal engineer with some knowledge of structures.

The mear fact that nastyjone's swinger does not have a cross brace at the radius of the tire has weakened the swinger by about 50% from what the brace would provide (the bending and twist moment arms are 50% longer without the brace).

So at the very least if the only thing that was different was the material stiffness, figure a 50% penalty for this lack of cross brace.
 
tkent02 said:
And they are engineered by real engineers, welded by real welders, and braced appropriately.
Click to expand...

Point well taken about bracing in the front of the swingarm. On second review, I'd add something up near the pivot...like the stock swingarms. I still think the legs will be okay, but bracing the front, with some extensions down the arms would stiffen that thing up significantly. One other question is the axle length at the rear, looks like the swingarm legs are splayed wider than necessary.

Edit: How do you guys like my paint job? Poor mans CAD.:)

swingarm.jpg
 
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BTW, I'm a mechanical engineer so I know what I'm doing.^o My consultation bill will be coming in the mail.:D
 
BTW, I'm a mechanical engineer so I know what I'm doing.^o My consultation bill will be coming in the mail.
Click to expand...

Well now you have really gone and done it:( . Instead of folding on a 40 mph corner where it would have been relatively safe, now we are looking at a 60 mph highside :eek:

Full leathers with a racing hump advised :D.

Pos
 
Mannn, all this talk of stiffness and elongation has me a little concerned as to the content of the thread. :eek: :p

POS you do have some genuine concerns but keep this in mind: the moment needs to be chased all the way around the structure. In this case (with the spring/shock combo located at or near the rear axle) there is more vertical surface area (add the trig and call it a day) than in a mono shock configuration. Were it a mono shock set up, I would be worried. :-#
 
Were it a mono shock set up, I would be worried. :-#
Click to expand...

Ironically, if it were monoshocked, he would have at least cross braced the swinger (for the lower shock mount) improving the stiffness by some 50%.
 
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