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Author Topic: Cartridge Emulator Installation  (Read 606 times)


  • Grand Gearhead
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Cartridge Emulator Installation
« on: September 08, 2012, 03:04:55 PM »
The following is pasted verbatim from my post on Ace's page; thought it might be of interest.  Apologies for a lack of pics on my end, but the instruction sheet with the product has a good set of diagrams.  (Edit:  I just attached it to this post)


Long time coming, but I finally installed the YSS cartridge valve emulators.

Executive summary--FANTASTIC! But you may need to do a little more work than just pop them in. Still a hell of a lot easier than a front-end swap.


I've seen reference to them as a Racetech clone but I have no personal idea, and don't know how much the Racetechs cost. These were $135, plus $10 for cutting
me some spacers. Believe they're made overseas. (Thailand, I think I once read?)

My fork is the old-school Bullet fork from the 1977 model year, with the screw-down oil seals. Can't speak for all bikes with all forks, obviously, but most of the Bullet forks seem to share the same basic configuration and operation.

I took measurements from a disassembled fork and Klaus at YSS tech support in NJ told me the 29mm would be a perfect fit.  (AMENDMENT:  The 29mm valves will not fit in the disc fork I just tried to transfer them into!  Looks like 28mm or less will be necessary; next size down seems to be 26.5mm.)


Basically, the procedure is to drill extra holes in the pumping rod ("hollow stud" or "spring stud" in the fork leg in most Bullet technical manuals) to allow oil to move freely; the cartridge emulator then provides all your damping via a speed-sensitive shim stack. On the Bullet, you drill out the existing bottom hole to 8mm (or 5/16") and then add three more 8mm holes on top of it.

The emulator itself is a small cylinder with an adjuster screw coming out the top. It sits on top of the pumping rod and under the spring, trapped by light spring tension at rest. Because of the nut on top of the pumping rod, you need to add a cylindrical spacer to give the emulator a place to sit. (Some other makes' rods have a cupped shape on top, so they don't need this.)

Klaus provided me PVC spacers, but they ended up being 1) too thick-walled, and covered up the existing rebound valving holes 2) too short, according to Klaus, when he saw how the rebound system operated; he said the oil needed more space to flow. So I got thinner steel ones machined...17mm high, about 1.5mm-thick
walled. They fit perfectly.

So, the valve was around 14mm tall IIRC, and the spacer was 17. Obviously, this height shoved under the spring was going to add an intolerable amount of preload to the spring. I simply had the springs cut to correspond and ground flat again, taking the spacer/emulator stack height off the top portion of the coil. This portion is static; the coils are touching one another and don't add anything to the operation of the suspension, so it's no-loss.

In reassembly, I used 200ml of 20wt Motul fork oil. 20wt is all I can find locally so I gave it a shot.

Initial Evaluation:

When I got the front end buttoned back up, I was a bit concerned. It felt like a rock at first. But you need to remember suspension is not designed to feel good sitting still. (A common problem with mountain bike suspension...they under-spring and under-damp because they know most punters will just buy whatever feels squishy on the showroom floor!)

I was a bit cautious for about 30 seconds on the test ride before I was blasting over speed bumps at a pretty shocking speed [Enfield-relatively speaking...]  The speed sensitivity of the valving is obvious once you're moving. Took the rough choppy stuff and big humps just fine at speed. I picked my way down some ledges and steps, and the bike took them nicely...soft landing with good
progression mid-stroke.

The valves were set with 2.5 turns preload on the shim stack adjuster screw(2 being the stock recommendation for lighter riders...I am 160 lbs.) Oil weight is the only way to control rebound and the 20wt was suitably fast.

Overall, a rider on smooth pavement might like a bit more cranking on the adjuster screw, or maybe a higher oil height for greater progression, but for India's chopped-up roads this setting felt great for a start. The front of my bike feels better than the Hagons on the back now.

Unfortunately, you need to open up the fork to change settings, but even as it is, it's a massive improvement, so I will likely ride it like this until my new fork bushings show up. Then I'll add a turn of preload and see how it does.

I'll re-post if there are any future problems or revelations.

Website for the product is: http://www.yssusa.com/products_yss_pdforkvalve.html
« Last Edit: March 18, 2014, 03:38:41 AM by AgentX »


  • Bulleteer
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Re: Cartridge Emulator Installation
« Reply #1 on: September 09, 2012, 07:01:49 PM »
This is fantastic news! Thanks for sharing AgentX  !  I'm very interested cuz I'm not happy at all with the shocks on my bike. Have you noticed if the the heavy diving when breaking hard has lessened after the up grade?


  • Grand Gearhead
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Re: Cartridge Emulator Installation
« Reply #2 on: September 10, 2012, 05:25:24 AM »
Yes, there's less dive now.  I never had a lot of it before, but my fork (it turns out) had some elastomer top-out bumpers installed, which decreased shock height and increased preload...this may have helped me in that regard, even prior to the installation.

You can tune the valve, so you can stiffen the damping if that's your preference.

The valve doesn't have separate high speed and low speed compression damping adjustments, however, so you can't really tune out brake dive specifically without making the fork overall less compliant.  Generally, I'd guess that only top-end super-modern bikes have separate high and low speed compression circuits.