Vintage Ness Styled Springer Project - Page 2
We cut these trees and the spring bridge with the water jet and cleaned up the holes with reamers but if you look back at the original old school Springer build article you'll see that these parts can be quickly and easily cut just using a reciprocal saw. The trees are from 5/8-inch stock and the bridge is from 1/4-inch material, all hot rolled.
All we've done so far is to clean up some of the holes and sanded off the heavier mill scale. The parts will be polished later on down the line.
We'll post links to patterns in Adobe pdf format that you can use to do layouts on your own steel a little later in the article.
For time being however all we want to do at this stage of construction is to prepare a mockup of the parts that we can use to determine the exact lengths of legs needed for our particular bike.
The next thing was to bend up some front legs. I just used cheap 3/4-inch 16-gauge steel tube from Home Depot.
These were bent pretty much by eyeball on the prototype of the CBH vertical bender. They aren't perfect but close enough for what we need them for at the present time. Some people call these 'coke-bottle' legs but to me they don't really look like 'coke-bottle' curves so I just call them 'bent-legs'. For those not familiar with Springers these are the 'front' legs, typically called the 'sprung legs'.
Next is just to hack together a rough mockup of the frame and forks. Here we just shimmed the frame up on blocks and got it to set at what we want to be the final actual ride height, front and rear. In most cases you'll want the lowest portion of the front of the frame to be about one-inch higher than the lowest portion of the rear of the frame. Some folks like the front even higher. The ride attitude is a personal thing so set it it up however you want it to look when it's on the road.
It helps if you have the rear wheel and tire mounted. My wheel assembly is on another guys bike right now but I know what the rear axle height is so in this mockup it wasn't a problem.
Some of you eagle-eyed visitors have probably already noticed something else that's a little different on a Ness-styled Springer compared to a conventional fork set. It's the length of the lower compression springs. Normal Springers typically use a 6.5-inch lower compression spring but the Ness/Century forks used springs that varied from 7.5 to 8.5-inches in length depending upon the vintage of the forks. They are also about a quarter of an inch smaller in diameter than most springs. I've seen guys building these forks with the short Harley springs and to my eye they look like crap since the front leg spring bridge is above the lower fork tree, just the opposite of what you normally see on a Springer of any type.
While we're at this stage of the project it might be a good idea to talk about fork length in general since there is a lot of mis-information out there on the web. The table below is taken from the alignment section of the H-D manuals and lists the factory lengths of various fork assemblies:
So that we can compare identical numbers this table is set up so that all measurements are taken from the uppermost surface of the lower tree (bottom of the lower bearing dust shield) and then down to the center of the rear leg rocker pivot point on Springers and to the axle center for hydraulic forks.
As you can see from the table when somebody says they want a set of "3-over" forks they need to clarify that measurement against some type of known stock H-D fork to begin with. To make it easy for manufacturers most companies adopted the old original FL Springer as the basis for all Springer measurements and the 1980 FXWG as the basis for all hydraulic fork measurements. To make things even easier most makers also adopted a dimension of 8-inches as the so-called 'standard' neck length (measured from the top of the lower tree to the bottom of the upper tree).
This system works out just fine as long as you're ordering hydraulic forks or Springer forks that use 'stock' rockers but what happens if you want a Springer with 'custom' rockers like the various types offered by custom builders?
The sketch below illustrates some rocker alternatives.
The drawing shown at the top of the sketch represents a typical 'stock' type rocker. Note that the axle hole is 1-inch below the rear leg pivot point. The drawing in the center of the group represents a fairly typical 'aftermarket' type rocker with the axle hole extended slightly forward (to improve trail) and level with the rear leg pivot point. The drawing at the bottom of the group illustrates another fairly typical type of 'custom' rocker. This time the axle hole is extended both forward and upwards (to improve trail and reduce flop).
Keeping this in mind, if you simply ordered a 3-over Springer but also wanted to used the 'custom rocker-2' style rockers your bike would actually sit two full inches to low in front compared to using the stock rockers. If you used rocker style 1 the bike would still set one-inch to low.
The point is that you need to have some idea about what type rockers you'll need for your Springer project to keep both trail and flop within reasonable ranges before you decide on the actual length of the rear leg tubes.
Most custom builders are aware of these issues and if your order a 3-over set of forks they will automatically factor in the extra length needed in the legs to accommodate whatever rockers they decide to supply with your forks. Unfortunately there are some outfits out there claiming to be custom fork builders who still don't have a clue about making proper forks so shop wisely if you decide not to build your own hardware.
For the forks we are using in this article the rear legs will be the typical 1-inch o.d. as used on the original forks but following the lead set by Chassis Builder Jim Davis when he took over the production of the Ness forks we'll be using tubing instead of solid stock. At this point it's probably a good time to talk about tubing verses solid stock since everybody has a personal preference.
I've built forks using both solid and tube legs and my personal opinion is that tube forks have a far better ride and 'feel' than solid legs. An aerospace engineering once told me the reason that tube legs seem to behave better than solid legs is because there are four axial surfaces at work instead of two so harmonics are dampened better. I don't really know about that but I do think that a set of forks with tubing legs send far less 'messages' up into the trees and handlebars than forks using solid legs. As to strength, if you do the math, a solid rod has very little little advantage over a tubing section so long as you keep the section modulus close to the same number.
In the end the final determination between using tubing or solid stock actually comes down to what you were taught to use. Most of the guys I worked with like Ed Roth and Dick Allen leaned towards hollow tubing, especially on long forks, so that's the direction I took in most of my past work. If I had access to a lathe in my early days I might have gone towards solid stock as it makes building legs a 'no-brainer' and my personal opinion is that those builders who still use solid stock for legs do so because of 'production' reasons and not for issues related to strength.
Keep in mind that a lot of us are building very 'long' forks using relatively thin wall tubing, nothing as massive as what we're using on these forks, and so far after about 40-years nobody has broken anything so I can personally testify to the strength of DOM tubing for fork legs.
I still get a lot of mail about this particular issue from people who claim that using tubing is a 'death-sentence' but that's usually from the same bunch of people who are running with extended hydraulic forks. What are hydraulic forks made from?
Since we're not using a lathe to turn the legs we need to come up with some method of making the 'spuds', as they are often called, so we just machined end-pieces that have a tang that inserts into the hollow of the tube leg. The tang is plug-welded and then the junction between the leg and spud is deeply welded. The rear legs seen below haven't been welded yet.
If you're building at home without access to machine tools you can use the pivot point end-pieces as we've described in the 'Old School Springer Build article.
More to follow ..................................................
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