Cartridge emulators for 1970s forks

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David Lahey
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Re: Cartridge emulators for 1970s forks

Postby David Lahey » Sun Oct 13, 2013 10:08 pm

finally got to do a good comparison test of the fork action with the Gold valves. Immediately before a trial today I went for a ride on a bike with standard TY250 forks, following a specific course, then I rode the same course on the bike with the TY250 forks with Gold valves. Then I rode the trial on the bike with the TY250 forks with the Gold valves, then straight after the trial I rode the bike again with the standard TY250 forks.
The forks with the Gold valves worked noticably better on stream-bed stones, and on other smallish obstacles like fallen limbs, roots and small tree trunks. Big obstacles and grippy dirt didn't seem any better or worse than with the standard forks. It might be useful to get some slow motion footage to compare the fork action from one bike to another but I don't have a suitable camera.
I now want to try a set of gold valves on a different set of forks - maybe the KT250 forks


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Geoff Lewis
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Re: Cartridge emulators for 1970s forks

Postby Geoff Lewis » Thu Oct 17, 2013 7:57 pm

Hi David, Could you explain where in the forks these things go and will they work on very basic forks with crude damping rods like on my CZ's. or other oldies? Or are they only suited to later Japanese and Euro bikes. Do they screw onto the top of the damper rod? or underneath? Are they expensive?
Regards, Geoff.


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Re: Cartridge emulators for 1970s forks

Postby David Lahey » Thu Oct 17, 2013 8:50 pm

They sit between the top end of the damper rod and the suspension spring, and have a low friction sealing ring that seals against the inner surface of the fork tube. They are held in place by the load on the suspension spring. They are made in different diameters to suit the different IDs of different fork tubes. Any Ceriani copy forks with internal springs should be suitable. I haven't seen inside 1960s CZ forks. In the case of the TY250 forks and probably many other 1970s Japanese forks, the spring seat has to be cut off the top end of the damper rods, so that the oil path is changed to being straight along the centreline of the forks. Another mod required is to increase the number of oil holes in the bottom end of the damper rods, so that all the compression damping is done by the gold valve, rather than through the bottom holes. Because the damper rods are shortened, and because of the height of the gold valves, the existing spring preload spacers need to be resized to achieve the same suspension spring preload setting as before.
They say in the instructions that higher rate springs might be needed after fitting gold valves, but I did not find this in my case. I suspect that the instructions are mainly intended for fitting gold valves to MX bike forks, where the reduced high speed compression damping might need to be compensated for.
Gold valves have no effect on rebound damping, so rebound damping can still be tuned by changing the fork oil viscosity. I don't hop the front end, and TY250 forks are already quite under-damped in the rebound stroke, so I used 15WT oil, and may try heavier grade oil later on. The instructions claim that changing oil viscosity has very little effect on compression damping with the gold valves in place, so there lies an opportunity to tune the forks for heavier rebound damping.
The one set of GOLD valves cost me about $200, and there are also YSS brand emulators available which I have seen advertised for $175.
The forks have to be completely disassembled so combined with the machining, it would probably cost 2-3 hours labour to do the installation if you had to pay someone to do it.


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Re: Cartridge emulators for 1970s forks

Postby Guy53 » Sun Jan 12, 2014 1:47 am

I've been checking for update on this thread since it was posted . The std fork on my TY ts are basicaly original exept for a mod on the the lower aluminium '' plug '' at the buttom, and are far from confortable on river bed or rocky section. I was planning on drilling the holes on the damper rod but I am looking at a less '' let's try that '' solution.
As you mention , David, the modified fork on your majesty felt more like Mono fork and felt a bit like the one on a later Bultaco, after a while, do you think the same way ? I am a phone call away from ordering a set of Gold Valve ( the part # FEGV 3004 for a TS Yamaha, can you confirm ? ). This year, suspension tuning is the project, first the fork, than the rear shock as I don't think my NJB shock are at there best or if they are a new set of better quality will be on the wish list.

Guy



David Lahey
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Re: Cartridge emulators for 1970s forks

Postby David Lahey » Sun Jan 12, 2014 8:32 pm

Hi Guy
I had forgotten about this forum string so thanks for reminding me. Since my last post on this topic I rode two more trials on that bike, and both trials featured slippery rounded streambed rocks, as well as larger obstacles, so were a good test for the fork setup. The front end worked as as well as I have ever felt on 1970s forks so I am planning to stick with the same setup I mentioned earlier on that bike (250 Godden Majesty).
Since then I have learned that people have been doing interesting things with damper rods to improve the action of these sort of forks in VMX racing. The intention is to create an effect where the damping effect is reduced for the part of the stroke when there is not much compression load on the forks, but retain the standard damping in the final stages of compression of the forks. I am keen to do some experiments with this idea on another set of TY250 forks or KT250 forks but haven't started yet.
As far as the Gold Valves go, I can recommend the settings I mentioned for TY250 forks as being a pretty good thing, but of course modifying the damper rods instead would save a lot of money, and may be just as beneficial. I'll look for the part number for the Gold Valves I bought later tonight


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Re: Cartridge emulators for 1970s forks

Postby Jansk » Sun Jan 12, 2014 8:52 pm

Hi David,
I have been following this thread for a while with quite some interest. Can you elaborate on these damping rod mods you have learned of?
2 shocks are better than 1.



David Lahey
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Re: Cartridge emulators for 1970s forks

Postby David Lahey » Sun Jan 12, 2014 9:13 pm

The Gold Valves I fitted are FEGV3004


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Guy53
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Re: Cartridge emulators for 1970s forks

Postby Guy53 » Tue Feb 25, 2014 10:16 am

Just got the Cartridge Emulator today and I will start the mod., either this friday or the next. Any last minute advise?

Guy



David Lahey
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Re: Cartridge emulators for 1970s forks

Postby David Lahey » Tue Feb 25, 2014 10:35 am

Guy, I'm quite happy with the action as it is, but will soon be trying with the spring preload fully backed off ie with zero preload on the emulator spring, to see if the action can be made even better


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Guy53
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Re: Cartridge emulators for 1970s forks

Postby Guy53 » Tue Feb 25, 2014 12:04 pm

I read and re-read the instructions and I cannot understand the part where I have to machime the top part ( aluminium part where the spirng seat ) . Do I have to cut it the lenght of the emulator ?

Guy




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