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Author Topic: Race Tech cartridge emulators install and test  (Read 635 times)
Spurlock
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« on: April 27, 2018, 08:55:10 PM »

In the past I've installed Race Tech's gold valve cartridge emulators on two NX250s and my GB500 with great results, so I decided to try them on the CB-1. First, in answer to the question, "What the heck are cartridge valve emulators?," this link to the Race Tech site explains it all:
http://www.racetech.com/page/title/Emulators-How%20They%20Work

But the basics are: Damping in old style damping tube forks is accomplished by forcing oil through small orifices. When riding over a bump at low speed, the damping of the forks' compression stroke will usually be very light, allowing the forks to compress and absorb the bump. But for harder hits at higher speed the forks will begin to compress very fast. But the resistance to oil flow through an orifice increases as the square of the compression speed, so the compression damping effect goes sky high when hitting square edged big bumps. Bottom line is, you don't get full benefit of the available fork travel because the forks can virtually hydraulic lock. By using spring loaded valving, the cartridge emulators convert the compression damping system to one that is speed sensitive, so that as the speed of fork movement increases the damping force stays consistent, giving you the benefit of maximum suspension travel right when you need it most. This mimics modern cartridge-damped forks which use flexible washers or similar to control oil flow. With the emulators, rebound damping remains controlled by the stock orifices which works well enough since rebound speed is fairly constant, rebound being only powered by the fork springs.

As with my other installations I took some (crude) measurements of fork response to big bumps for a before and after comparison to help in fine tuning the emulators. For this I use a (primitive) fork travel gauge consisting of a steel rod clamped to the fork slider....



....and passing through a metal bracket attached to the handlebars at the top. A trimmed down wooden clothes pin records the maximum compression of the forks after hitting a bump.



So I first headed out on familiar roads and deliberately hit the worst mis-matched pavement joints and pot holes on my usual routes, stopping to record the fork travel and speed at each one. Next came pulling out the damper tubes from the forks. On the CB-1 it's not necessary to pull the fork tubes, only the Allen screws at the bottom of each fork slider along with springs and spacers and dumping the damping tubes out the top. Next, extra compression damping holes need to be drilled in the rods so the job of compression damping will be handed over to the emulators which are "downstream" from the original compression damping holes. There are four existing 8 mm holes and two more need to be drilled. To make sure the original holes would no longer be functional, I enlarged all six holes to approx. 9 mm.



After deburring the holes inside and out and thorough cleaning, I chose springs and damping plates. The kit comes with three different springs with different rates. I weigh only 150# with gear, and would classify my riding as "sport touring", so I like a suspension that is compliant but not mushy. I chose the lightest (blue) springs), and set them up with two turns of preload. Spring rate and preload determine the point where the valve plate opens during fast fork compression, and how far it opens. The emulators are easily fished out of the top of the forks later for fine tuning if needed. Low velocity damping is handled by the small holes in the valve plate. I chose the plate with four holes rather than only two.



The emulators sit atop the damping tubes and are held in place by the fork springs, so due to their thickness they add about 16 mm of preload to the fork springs. Static sag with my stock springs was 26% before and with the emulators is now down to 17%, leaving more fork travel available when hitting bumps. I reassembled the forks, added the same type oil as before and went out for the "after" measurements. Since rebound damping is unaffected by the emulators, it is first adjusted by choice of oil viscosity if needed, before tweaking the emulators to fine tune compression damping. I was happy with rebound action using ATF so I stuck with the same brand as before.

The result? Fork travel on the same mismatched pavement joints and pot holes increased by 25% - 33% making the ride less harsh while fast bumpy corners actually felt more controlled. But by the butt dyno gauge I feel an obvious difference in response between front and rear. I am using the Blackbird rear shock, and before when hitting the same sharp bumps I would feel equal hard hits as the front and then rear wheels passed over, like bam-bam. Now the front feels compliant and the rear feels harsh by comparison. I have the spring preload and damping set to minimum on the BB shock, but for my light weight and ride preference I feel it is too firm and had already ordered up a new Hagon before installing the emulators up front. So now I'm anxious to experience an improved back end as well!

-Bill
« Last Edit: April 27, 2018, 09:11:13 PM by Spurlock » Logged

1975 Honda CB125S2, 1989 Honda NX250, 1989 Honda GB500, 1989 Honda CB-1
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« Reply #1 on: April 28, 2018, 08:45:58 AM »

Nice writeup Spurlock.  I've always wondered what was involved with installing those emulators and how exactly they worked.
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1979 Honda GL1000 Goldwing - 1990 Honda CB1
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« Reply #2 on: April 28, 2018, 08:06:05 PM »

Thanks, Bill! As always, an exemplary write up. I like the clever travel gauge you devised.

Does this mean your BB shock will be for up for sale? Would it be better suited for for a 190# geared rider?
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Spurlock
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« Reply #3 on: April 28, 2018, 08:31:26 PM »

Thanks, Bill! As always, an exemplary write up. I like the clever travel gauge you devised.

Does this mean your BB shock will be for up for sale? Would it be better suited for for a 190# geared rider?

Thanks Rick,
Yes, more than likely I will sell the BB shock. I believe it would be much better suited to a heavier rider since I have the spring preload backed way off. Are you interested? If so I will give you first choice and will PM you if/when it's available.

-Bill
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1975 Honda CB125S2, 1989 Honda NX250, 1989 Honda GB500, 1989 Honda CB-1
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« Reply #4 on: April 29, 2018, 03:06:27 AM »

Interested. PM me when available  Wink
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Spurlock
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« Reply #5 on: April 29, 2018, 11:52:51 AM »

Interested. PM me when available  Wink

You got it Rick.

-Bill
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1975 Honda CB125S2, 1989 Honda NX250, 1989 Honda GB500, 1989 Honda CB-1
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