damper rod fork modifica\tions

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Tramp
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damper rod fork modifica\tions

Post by Tramp »

okay techno guys and girls..
my xt660z now runs 6.0nm linear fork springs with yss cartridge emulators similar to the dr650 cognet valves , im running 5w fork oil with correct flow rate tried 2.5w but got too fast rebound..

the trouble im having is on roads at 50mph over any surface they are brilliant..but at slower speeds 30-40mph over harsh bumps or drops I get hits through handle bars....now to me that sounds like lack of fluid flow but hit same bumpsat 50mph and its fine...

on trails same effect slow speeds give harsh bumps..fast and its all roses..

anyone got any input please..im running std damper valve holes ...with sts yamaha fork oil quantity and corect sag with just 1 turn preload out of 27..

its doing my head in.
Seminole
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Re: damper rod fork modifica\tions

Post by Seminole »

Sounds like the spring rate is a tad high for you, lost weight?
garyboy
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Re: damper rod fork modifica\tions

Post by garyboy »

I would guess that a 10W oil would be better?


5W sounds way too low ... at low speeds you are going slow enough for the forks to bottom out somewhat.
higher speeds you are going too fast for the forks to have time to react?



also the 6nm spring rate is lower than the stock 7.2 (I think) in my 250 rally, and that is way too soft!!

= .72 kg/mm (stock) [for the L]
Bart1
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Re: damper rod fork modifica\tions

Post by Bart1 »

Can you adjust the spring on the emulator ? backing it off would let the valve open sooner ie let more oil through with less force required.
catcitrus
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Re: damper rod fork modifica\tions

Post by catcitrus »

I run Race tech emulators--both the emulator valve spring and the preload can be changed/adjusted. The valve responds to the rate of compression and opens up more as the pressure of the oil rises giving you a more progressive damping response--a simple damper "hole" tends to make the fork go "solid" as the oil flow through the hole goes to a maximum on hard bumps. With the emulator the valve orifice size increases still allowing oil flow commensurate with good high speed damping. It sounds like you have the opposite with insufficient damping at low speed?--what does it feel like when bounced hard when stationary--should have plenty of damping like this. Maybe try increasing the damper valve preload a bit. With the Race tech emulators the fork springs have to be shortened slightly to avoid increasing preload due to the emulators taking up spring length--also the traditional damper tube holes have to opened right up to have no additional effect. How was your " kit " fitted?
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Re: damper rod fork modifica\tions

Post by Magnusson »

Try the tie-rap trick to see how much fork travel you are getting.
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Tramp
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Re: damper rod fork modifica\tions

Post by Tramp »

The yss is similar to the other valves in that it has a large disc for fast flow and 2 smaller holes for slow speed oil flow ...it's set at 2 full turns in tried 4 turns was ...far too restrictive..

Firefox racing and ktech UK helped develop the set up too so very good guys...the damper rod fork holes are unchanged unlike Ricor types as we use thinner oil to bypass them ...like the cb500x do from rally raid although they use custom damper rods lol...

I will try to find some second hand xt660 damper rods and experiment lol...

We have 6 guys worldwide with same set up so some different responses ..from different riding styles..

We also accounted for the extra length of yss pd valve and seating spacers...its all same as yamaha spec so we have a good comparison...went from 4.5nm to 6.0nm springs ..ohlins do a similar one....the spring gives excellent static sag of 30mm and rider sag of 50mm...so within spec for total fork travel....

We want from 10w to 5w and even 2.5w fork oil all putloline race synthetic to give good cst @40c...but the 2.5w gave far too fast rebound...and 10w too slow..
catcitrus
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Re: damper rod fork modifica\tions

Post by catcitrus »

If the original damper holes are still there then what is taking priority?---the holes or your emulator?--I don't know the set up but it seems pointless to put an emulator in when the high speed, high load damping is compromised by the hole diameter and the system is basically hydraulicing . That was my original problem on a Honda but when I drilled out the damper holes and fitted the emulators high speed landings off jumps were vastly improved--and that was a CRF 230 on an enduro track ! (not its intended use).What were the fitting instructions, and what is the reasoning behind fitting the emulators WITHOUT removing the original damping control?
Tramp
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Re: damper rod fork modifica\tions

Post by Tramp »

Well some say open up to 8mm the btm compression holes so bypass them leave top rebound at 4mm others firefox and cognet usa say go thinner oil and leave holes as the thinned oil flows faster...

But rallyraid together with tactive suspension in Holland on the cb500x went with a new damper rod larger holes and thinner oil...and emulators....

There are so many variables the only one I've not tried is enlarge holes...so I'm trying to find a used xt660 damper rod to try.

Only so much you can do with basic forks....the rear yss shock is excellent.
Thanks for the feedback from someone who has tried ....
Bart1
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Re: damper rod fork modifica\tions

Post by Bart1 »

The emulators only affect the compression circuit, so if thinner oil is used the rebound will be too fast as it still flows though the original rebound damping hole near the top of the damper rod. Therefore the only way to control rebound damping is with oil viscosity.
To allow the emulator to work the damper rod holes at the bottom need more area, either bigger holes or more holes.
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