I need your help! Could you please take a couple of measurements of your frame and note your model number?

Info needed:

Model code stamped on frame (first two numbers)

Outside-to-outside distance between the frame flanges that have the swingarm pivot holes

Distance from front edges of spindle holes to front edges of flanges (mine differed by 1/8")

I'm trying to determine if there is any difference in this area between the different models built, so that I can build spindle kits accordingly.

You can reply here, PM me, or e-mail at grandpaulz@hotmail.com

I really appreciate it.

I think there is a serious and maybe dangerous flaw in your redesign of the Norton featherbed swingarm pivot.

In both the standard street featherbed and the Manx racing featherbed swingarm designs, the through-bolt can be tightened to a torque specified for that diameter and length of fastner. This puts makes a tremendous clamping force pulling the two frame gussets together and in effect creates a frame cross-member. With the Manx setup, which has a larger element going through the swingarm from gusset to gusset under the tension of the through bolt this effect is better than the street bushing setup.

If anyone knows about pre-stressed concrete, where steel cables are drawn into great tension by winches while concrete is poured around them and left to cure, when the winches are released the tension pulling the concrete beam etc. together makes it very much stronger than it would be otherwise.

With modern rubber the featherbed frame is flexing more around the rear swingarm area than it ever did, this is one of the most frequent areas of cracks and breaking up of the frame in competition events.

If I understand your new design, it eliminates tightening of the through spindle any more than is needed to set side play? This also eliminates it's clamping force along with eliminating a mechanical element going through the swingarm pivot that is under this compression, clamping the two frame gussets together and stiffening the frame considerably.

If that is true, your new design is going to have much more flex in it than any standard featherbed parts and the bike is going to handle worse, the extra flex is going to wear, bind and have the frame crack much easier and sooner in use.

To have independent half-spindles work on a motorcycle swingarm, you would have to have a frame that does not depend on the swingarm pivot for part of it's already marginal stiffness.

The stock silentbloc setup works fabulously for street bikes, even hard ridden ones, and the Manx setup has carried racers around tracks in the past at speeds that 99.99% of riders will never ever see.

As you state in the other thread on your fabulous Triton "I want my Triton to be MY Triton". Looks like another instance of ego and style in the neo-cafe bike scene taking precedence over function, engineering and intelligence.

Ego and style. Where would we be without those?

Not snoring around on Tritons!

Actually, with the off-side end plate drilled at the reduced diameter of the fastener, yet both frame webs drilled at full spindle diameter, my retrofit kit does indeed bolt up to form an extremely rigid frame crossmember. Not only that, it is one that is not forcing the downtubes together any more than the manufacturer's spacing variance (which I am finding to be about 1/8" inch in three frames measured so far).

Unless the original setup incorporated a spacer between the bushings, any torquing of the spindle beyond a very slight tension would immediately start placing a detrimental bind on the swingarm's free movement in the OEM configuration.

I've been called potentially dangerous and deadly at least once before, so this is certainly nothing new to me.

Caveat emptor and all that...

grandpaul wrote:Unless the original setup incorporated a spacer between the bushings, any torquing of the spindle beyond a very slight tension would immediately start placing a detrimental bind on the swingarm's free movement in the OEM configuration.Caveat emptor and all that...

How could you not know that there IS a spacer in the original design between the bushes? You have had your hands on these parts right?



Also you are still missing the flaw in your design. For a motorcycle chassis to be rigid between the steering head and swingarm pivot, it has to have either very rigid and large diameter elements between the two, as it the case of the large alloy castings and large cross-section members of the Yamaha Deltabox design, or if the elements are not rigid and small in cross-section, then they have to be assembled in a manner in which they use triangulation for rigidity, as in the case of the Ducati superbike ladder frame of the 1990's etc..

The featherbed frame has a very little bit of both rigidity and triangulation, just enough to make it really good for 50-60 bhp and small section tires. The featherbeds triangulations are long and flimsy, and the rigidity of it's non-triangulated elements is marginal.

The long through-bolts of the swingarm and of the rear engine-fixing cross tube just above the swingarm, need to be torqued to SAE specs to stiffen up the rear of the frame and get the most out of the chassis.

Among other sins, the AMC works eliminated the fastner through the rear engine fixing member on late slimline featherbeds and just welded it in place, saving the company a few pennies per frame, but making it less stiff by eliminating that clamping force and vulnerable if one of the welds should crack.

Paul, it does not matter if you put a four-inch spindle on the featherbed frame. Because if it does not clamp the gusset plates together it is doing nothing to add to stiffness, and it can not rely on the frame for stiffness because it has none unless it is assembled as designed with all it's subtle elements in place, one of which you have eliminated.

Caveat Emptor is what you have to say to your customers? Doesn't sound like you give a shit about them after you have made their money yours......

I have a hard time translating what is going on in my head, and in my shop, so I do it with pictures. Suffice it to say I have 100% confidence in my design.

Installing a Triumph engine with bolt-up conversion plates is costing structural rigidity, so replacing the wimpy swingarm spindle with a beefier bit is adding just a little of it back into the picture.

My chassis came with one bushing in the swingarm, and an incorrect bolt holding it in place, I never looked at or considered the OEM setup for my project.

I believe emptors on this forum employ sufficient caveats, and most have come to know and understand me well enough to deal with me or stay away without being ungracious.

see below...

OK, I love a debate,
So just to add some more fuel to the fire I dug out my dial gauge and vernier calipers, here's the results, bear in mind I've got a wideline frame with a Dresda swingarm which runs on tapered bearings.
The first problem I found was that there are no torque specs in the Norton manual for the swingarm spindle.

Free play in the swingarm with the spindle nuts loosened off = 0.017"
Distance between the Gusset Plates with the spindle nuts loosened off = 8.41"

Distance between the Gusset Plates with swingarm spindle nuts tightened (zero play at the swingarm) = 8.40"

So now we know, the gussets get squeezed by 0.01"

Webby

An engineer knows that all fastners have SAE or equivalent torque specs that are to be used on any machine, especially ones that peoples life depends on.

Oh, and a real mechanic and engineer also has heard of a thing called a "shim", which is used to take up clearances between machine elements that have manufacturing tolerances.

You are neither. And the only reason this is a debate is because you don't have enough upstairs to see you don't have a leg to stand on.

Postby grandpaul » Sun Mar 06, 2011 10:20 am

"Installing a Triumph engine with bolt-up conversion plates is costing structural rigidity, so replacing the wimpy swingarm spindle with a beefier bit is adding just a little of it back into the picture.
I never looked at or considered the OEM setup for my project."

Yea, whatever you do don't look at the OEM design, a breakthrough design by brilliant engineers, just go ahead and start hacking it up and changing things because you are "comfortable" with it and you have to make it yours for the sake of profit and show.

Why would installing a Triumph engine cost rigidity? Everyone knows that a unit construction engine/tranny is more rigid than having separate ones connected by plates, that is why all modern bikes are that way. The Triumph lump is shorter than the Norton assembly and will need longer plates, but it's affect on rigidity is not even an issue compared to you eliminating structural members and features.

Not only does your design fail to clamp and tie the swingarm gussets rigidly together like the OEM setup, your designs alignment also depends on the gussets being perfectly parallel to each other, which you have already found is probably different in every featherbed frame out there. And apparently you can not even understand or see what you are doing, your design is worse than the stock street featherbed, and much less rigid than the early or late featherbed Manx parts.

If this is representative of your engineering, comprehension and reasoning ability then no one should touch your stuff with a ten-foot pole.


Your swingarm conversion is trash for cash.

In response to Beng's post,
Hi Beng,
I've gone back over GPZ's Triton build with pics of his swingarm spindle design and here's what I think.
Provided the butted end of the spindle is machined correctly to allow clearance for both gussets to take up the play in the swingarm I see no reason why the design would not work.
However, yes I do agree with you that IF the spindle was too long it would prevent the gussets from clamping and therefore leaving too much play at the swingarm.
As for the spindle attachment plates, how accurate they are in regards to swingarm alignment will depend upon how you fit them, lets say for example that the holes in the gussets are 1/16" out of alignment, what's stopping you from moving one of the plates back or forward by 1/16" to ensure perfect alignment even if this would mean slightly opening up one of the holes in the gussets. Surely this has to be easier than welding up the holes and starting from scratch?


Just my two cents

Webby

Thanks Webby, but you are missing the point. Any Norton swingarm will have play in it. There is deflection in the street-featherbed rubber bushes, and there is running clearance in the Manx bronze bush setup. Any machine spindle has to have clearance to allow for free movement or lubrication.

What Paul's conversion is eliminating is overall chassis rigidity, and this is because the two long bolts through the swingarm spindle and the rear cross tube above the swingarm need to be torqued tightly. When they are torqued they clamp the two swingarm gusset plates together very tightly against the cross tube and the swingarm bushings and spacer and add greatly to it's rigidity. That is easy to see and common sense.

Pauls design can not be torqued tight or it will seize up solid, it is equivalent to someone leaving the nuts off the swingarm spindle on the OEM setup, and anyone should be able to see why THAT will make the frame less rigid even if the spindle is a tight fit in the gusset holes.

Making the swingarm spindle a larger diameter does not mean a thing because the frame it is attached to is less rigid and flexing because of it's failure to clamp the frame gussets together.

beng-

understood.

Next unit to be built will take a 5/8 threaded fastener and associated frame web hole, and retain the 3/4" spindle diameter, resulting in a tight clamped fit, which may or may not need to be slightly shimmed depending on individual user's exact dimensions.

I believe mine is completely sufficient as the end bolted security plate provides the clamping basis. Yes, it could be stronger without the bolt-up plate. Bottom line is the remaining kits will have one less plate and two less fastener pairs.

Thanx for your input.

beng wrote:Making the swingarm spindle a larger diameter does not mean a thing because the frame it is attached to is less rigid and flexing because of it's failure to clamp the frame gussets together.

So, don't buy one

Jean

grandpaul wrote:understood..

Can you put up a modified drawing of your proposed improvements?