How To: Race Tech Gold Valve Cartridge Emulator and Spring Kit

In 1935, BMW released the R12, a watershed motorcycle most notable because it was the first bike offered to the public equipped with a hydraulically damped, telescopic front fork. Despite the many advances in motorcycle technology over the ensuing 75 years, the fixed orifice/damper rod front fork has changed little; a technician familiar with BMW's seminal design would have little trouble working on any variation that's succeeded it.

This isn't necessarily a bad thing. Damper rod forks are inexpensive to produce, easy to maintain, and-so long as cutting edge suspension isn't required-work quite well, which is why so many motorcycles continue to use them. Unfortunately, they have one inherent flaw.

The Problem
In the simplest terms, fixed orifice dampers control the natural oscillations of fork springs by pumping oil through a series of small holes. Because it requires some energy to force the oil through the orifices, the springs' natural tendency to rebound uncontrollably after being compressed is reduced, or "damped," so the bike remains controllable (rather than turning into high-powered pogo stick as it would if damping were dependent solely on internal friction).

The major flaw with the design is that when fluid flows slowly through a hole, resistance to flow is very low, so there's little damping effect. However, as speed (meaning damper movement, not motorcycle road speed) increases, the oil's resistance to flow increases at the square of its velocity-move the oil twice as fast and you'll get four times the resistance.

Taken to an extreme, this "velocity squared" effect can cause the fork to behave as if damping is nonexistent at low speed, yet literally lock solid when some impact- a pothole, for example-forces it to move rapidly. For a simple visual of the phenomena at work, look no further than your most basic fixed orifice damper-the common screen door closer. Allow the door to close under its own weight and it'll move smoothly; try to slam it and the closer will lock solid.

In essence, while fixed-orifice forks can be made to work decently over a fairly wide range, they'll only work perfectly over a rather limited range. Their action and the amount of adjustability will always be limited by the size of the orifice.

The Solution
Suspension technology has always lagged behind engine development, and by the late seventies suspension shortcomings were becoming a real problem, particularly on the racetrack. The solution that suggested itself was to vary the size of the damper orifice in response to the speed of the oil passing through. That way you could create suspension that was linear in action; supple and firm at low and moderate velocity, yet free from potential lockup at the highest (damper) speed. That's precisely what the cartridge fork, which arrived in the mid-Eighties, does.

The cartridge fork does away with the damping rod and its drilled holes, replacing them with a cartridge tube and speed-sensitive valves or pistons. Although I don't have room for a full explanation here (partly because each manufacturer has their own design), the short version is that pistons can adjust their orifice size quickly in response to oil pressure, and as such are able to deal with both large and small hits in a proportional manner. This makes suspension action smooth and progressive, and because valves are almost infinitely adjustable, suspension characteristics can be tailored to the individual rider's needs.

While the cartridge fork is undeniably a better device than the fixed orifice type, it does have a drawback: cost. Cartridge forks are more expensive to build than an orifice-damped fork so manufacturers have to charge more for bikes equipped with them. That's why they're more often found on machines that require premium suspension units, like high-end sport bikes and motocrossers, than on things like cruisers and standards.

Installing the Race Tech Gold Valve Cartridge Emulator
While I'm a huge proponent of cartridge forks, I'd be the last guy to suggest you replace your cruiser's OEM damper rod fork with one. I've done it a time or two and trust me, it's expensive and time-consuming. In my opinion, a better idea is to convert your damper rod fork to one that mimics the actions of a cartridge type, which fortunately is relatively easy and inexpensive to do.

The Gold Valve Cartridge Emulator is a device developed by Race Tech founder Paul Thede, that allows a standard damper rod fork to imitate the action of a cartridge fork, hence the name. (see the side bar for a brief description).

Installing the Gold Valve requires little more than lightly modifying the OEM damper rod, then dropping the valve into place, a procedure that takes less time to do than it did to write the foregoing paragraphs.

Although we installed our valves in a fully-equipped shop, we're going to assume that you don't have access to things like 1/2-inch air impact guns, so where appropriate, a "shade tree" alternative is provided.

By the same token, while we're installing our kit on an Electra Glide, the basic procedure is virtually the same for all bikes, so the following pertains to a majority of damper rod forks. I say 'majority' only because I don't want someone with a 1947 Vard telescopic fork conversion on their Indian Chief sending me an irate e-mail because Race Tech doesn't make a Gold Valve to fit.

Once the spacer has been cut, set it aside for a moment and pour in the fork oil, using the OEM's recommended viscosity and height (If there's any question contact Race Tech's service department and they'll provide a recommendation.)

Work the fork through a few compression/rebound strokes to bleed out any trapped air and recheck the fork oil level. Install the fork spring and preload spacer, double check the preload height, then install the fork cap.

From here on in it's just a straightforward reassembly of the front end, although I'd be remiss if I didn't provide the obligatory warning to work patiently, consult the shop manual as far as bolt torques go, and be sure to apply locking compound wherever it's called for. Remember this is the front end we're working on, so if something comes loose or is improperly installed it's going to get ugly quickly.

Tuning Notes
Suspension modifications are just like any other type of elective moto-surgery in that, if you cross the T's and dot the I's in accordance with the manufacturer's instructions you're pretty much on the path to a harmonious outcome, and that's particularly true in this instance. In my experience, Race Tech's recommended settings are usually right on the money. However, in some cases, fine tuning may be required, or you may just want to experiment and find out what happens when you add more or less preload to the valve spring.

In either case, my advice is to work slowly and methodically, making only one change at a time. It's easy to lose your way when working on suspension-"let me think, did adding fork oil make the fork more responsive or just mushy?"-so record each change and your impressions of what that change did to the bike so you don't get confused. If you do get bollocksed you can always return to the base settings so no need to be overly cautious either. Suspension tuning can be time-consuming, even with something like the Gold Valve, but in the end it'll be well worth the effort.

How the Gold Valve works

Low (damper) Speed
When the fork compresses, oil flows through the center of the OEM damper rod into the Gold Valve. As long as damper speed is low, flow is controlled by a small bleed hole in the Valve's damper plate. This provides a smooth, firm ride over gentle bumps.

High (damper) Speed
When something big whacks the fork, like a sharp or square-edged bump, it increases the suspension speed, causing the oil velocity and pressure to rise until it overcomes the Gold Valves check plate spring preload. This forces the check valve (plate) off its seat, which allows the oil to bypass the bleed hole and flow directly through the valve's ports. The fork is no longer bound by the physics of velocity-squared damping, so it behaves in a more progressive manner. The spring's weight and preload determine the GV's high-speed compression damping

Rebound Damping
Rebound damping is controlled by the fork's OEM rebound damping holes and check valve. However, since the Gold Valve doesn't restrict return flow and the stock compression orifices are now radically larger, the returning oil has an easier time reaching the rebound orifices, so cavitation (an influx of air) on the return side-always a potential problem when an orifice-controlled damper is overworked-isn't an issue.

Resources

RACE TECH
www.racetech.com
Race Tech suspension kit $259.99
Race Tech SW3 fork oil $29.99

Tool Box

A Bike Jack is prerequisite for this job; doing it on a milk crate is asking for trouble.

Appropriate hand tools: Sockets, Wrenches, Plastic Mallet, Hammer, Center Punch.

A 3/8th Electric Drill and a 5/16ths Bit. You might want an extra bit in case you dull or damage one.

A Pipe Cutter to cut the preload spacers to size.

A Small Rat-Tail File to deburr the drilled holes.

You'll also need a Drain Pan, Tape Measure, Flashlight, Lots Of Rags and Aerosol Degreaser (like brake clean or electrical contact cleaner).

I'd also recommend installing New Washers under the damper rod bolts; you can use OEM or over-the-counter copper or aluminum crush washers.

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