GSX-R 600/750 K6/7 Fork mod

[Pussy]

A year ago Gassit Girl and myself bought a new K6 GSX-R750 each. Great little bikes. The Showa forks on them are better, in my opinion, than the Kayaba forks on the 1000, as delivered from the factory.
I did notice after a short while a bit of a deficiency in the rebound characteristics of the stock Showas, especially the high speed. I ended up having the rebound adjusters screwed almost right in, but as that only controls the low speed side of things, it didn't really achieve what I wanted.
A call to Robert Taylor, and an explanation. Robert phoned me back a couple of weeks later. In that time he had put a set of K6 GSX-R600 forks on his you-beaut shock dynomometer, and identified that the rebound curve was indeed fairly weak. Leave it with me, he says.
After some thought, Robert comes up with a spec to re-valve the rebound stack. This he has now done, and the forks have been refitted to Gassit Girl's 750. The forks were also serviced with Ohlins 5wt oil.
What a difference! We still have the compression set to stock position, and the rebound to one turn out. The bump absorption is VERY plush without being mushy (firm but compliant), the low speed rebound is spot on, but more importantly, the high speed rebound glitch is eliminated. No more patter from initial too fast fork extension, and no more too fast extension with chicane type flip flops. And the whole action of the forks is super smooth.
We have left my bike stock in the fork department to do comparison testing. The difference is very noticeable. Gassit Girl and myself have done lots of bike swapping over the last few days to try the "before and after", the guts is the mod has worked a treat, so much so that Gassit Girl has told me to leave the bloody forks alone now, she likes them how they now are.
This mod will fit K6/K7 GSX-R 600/750. The cartridges in the forks are the same part number, only the low speed rebound control rod is different between the 600 and 750.
The modification costs around $500.00, including the Ohlins oil. Well worth it.
I'm happy to give any more feedback anyone may want

[Kendog]

Sounds great, I really hope I can make it over there to do some bike swapping soon. looking forward to comparing my exhaust and tuning changes (more on these soon in another thread :cool:)

[Pussy]

You're welcome, Kendog, to have a go on the bike. I'll warn you, though, you will more than likely want to shell out some dosh to Robert after trying the mod. By the time you get here, I should have a different mod on my bike for you to try as well

[Shaun]

#10 weight fork oil and .95 springs (120mm air gap as a starting point) only was all I had to do to a Suzuki for racing on the street's, like where you guy's ride!

So this option is a shit load cheaper than changing full dampning stack etc

However, after saying that, the tech work that Robert does, is very good! But this is a cheaper option if any one wants to try it

[Pussy]

I reckon that would make the low speed compression damping a bit too hard for my nana riding. The new characteristics of the damping action is a combination of comfort and good feedback

[Robert Taylor]

There are distinctions here,

1) Spring rate according to rider weight / height and how much weight has been pared off the bike for racing. The standard springs in the 750 are 10s and that suits most riders 75 - 80 kilos up to about 90 - 95 kilos, dependent on how early the throttle is opened and for how long.

2) 0ils with bigger centistroke numbers ( thicker viscosity, the sae ratings on bottles are roughly indicative only ) will flow less fast through the bypass bleeds but have very little effect when the shim stacks open.

3) Racers in fact require relatively fast rebound characteristic because they are arriving at the next bump a whole lot sooner, requiring quick recovery. Road and track day riders require slower rebound because of their slower forward velocity.

4 ) Tuning by viscosity with a modern shim stack cartridge is not really the correct way. Moreover, if you instal a thicker oil to ''tune'' rebound ( we are talking about cartridges, not damper rods ) it will make the low speed compression feel firmer. That is not always desirable.

The mod has corrected a very real problem with the latest k7 and onwards forks, LACK OF HIGH SPEED rebound due to a very soft shim stack. By incrementally and subtley firming up that stack it has also allowed the installation of a thinner viscosity oil, allowing more low speed compliance and ALSO allowing the rebound clicker to a position that allows adequate low speed flow.

There is ALWAYS a very fine window of position where the clickers should be set. If they are close to being maxed out inwards or outwards then you are compensating for a valving spec that is not suitable, FACT.

Inm the end event it is always a choice between a cheap fix or one that will work better

[Shaun]

There is ALWAYS a very fine window of position where the clickers should be set. If they are close to being maxed out inwards or outwards then you are compensating for a valving spec that is not suitable, FACT.

Inm the end event it is always a choice between a cheap fix or one that will work better



Agreeed!! RE costing as above, that is why I offer the alternative rather than the full monti, there are riders that do not want to spend what they have not got, but want a little better bike.

[Fatjim]

Yeah, I'm thinking the same may be an option for the SV1000. The stock weight fork oil is less than 5wt apparently. Would it hurt to stiffen up everything with springs and 10wt oil when your a Fatjim?

Currenlty the bike floats like a butterfly on smooth roads and stings like a bee on rough stuff. Worst of both worlds

[Pussy]

I've only ridden a couple of SV1000s, and found they have quite aggressive high speed compression damping. Thicker oil will make it feel worse. I'm certain there is a relatively low cost revalve mod available from Robert

[Robert Taylor]

Yeah, I'm thinking the same may be an option for the SV1000. The stock weight fork oil is less than 5wt apparently. Would it hurt to stiffen up everything with springs and 10wt oil when your a Fatjim?

Currenlty the bike floats like a butterfly on smooth roads and stings like a bee on rough stuff. Worst of both worlds

Its because the compression pistons have ports that are too small and there is a lot of inbuilt friction. Oil is NOT going to fix that. Its a choice of spending some money to actually do it properly and being delighted with the result. The ''cheap fix'' is almost always just that, despite what anyone says. It is also very important to differentiate between racetrack settings and compliant road settings that also offer decent ride height control.

[Robert Taylor]

Agreeed!! RE costing as above, that is why I offer the alternative rather than the full monti, there are riders that do not want to spend what they have not got, but want a little better bike.

You know, one of the first things people do is to fit a set of noisy cans ( there often seems to be money for that ) when the suspension needs sorting first.

[Shaun]

You know, one of the first things people do is to fit a set of noisy cans ( there often seems to be money for that ) when the suspension needs sorting first.


True, and normally the stearing head bearings need attention as well. ie, re grease, and tensioned correctly!

amazing how much a badly set up stearing head can effect a bikes handling

[Sanx]

<snip>...
This mod will fit K6/K7 GSX-R 600/750. The cartridges in the forks are the same part number, only the low speed rebound control rod is different between the 600 and 750.
The modification costs around $500.00, including the Ohlins oil. Well worth it.
I'm happy to give any more feedback anyone may want

Interesting. Thank you. I'll pass that on to my K7 750-owning mate who's never quite been happy with the suspension on his bike. Though, with Cowpoos' help, we discovered today that there's a disturbing amount of free play somewhere in the swingarm / shock linkage which he's going to get addressed first.

[Pussy]

The mod has been in for a few weeks now, and is great. The front end feels VERY planted, feedback is right up there, and comfort is spot on. The sag settings are of course set up for Gassit Girl, who is considerably less gravitationally challenged than me, but even set up that way, there is a night and day improvement over stock

[KS34]

Have any of you noticed on the 750 k6, in fastish corners the clipons/wheel turning into the apex all by it's self?

[Pussy]

Have any of you noticed on the 750 k6, in fastish corners the clipons/wheel turning into the apex all by it's self?

See the other thread, KS34. A friend with a K7 750 is having a similar problem. I suspect it is an alignment problem. Your average K6/K7 sem fiddy handles like a dream, especially with the mod Robert has come up with

[Pussy]

The modded cartridges have done about 5500km now. Another added bonus is showing up... markedly reduced front tyre wear. Mind you, if it is being kept in proper contact with the road, ie the suspension doing the work and not so much the tyre, it makes sense.
Waiting for Kendog to chime in with his impression of the mod... :whistle:

[Kendog]

Waiting for Kendog to chime in with his impression of the mod... :whistle:

I hated it.................

Cause it made me think about spending more money on my bike :mellow:
If I had the money I would love to put Ohlins on my bike, it really did feel so confidence inspiring riding yours.

Damn you Mr Ohlins.

[Pussy]

RT is fitting a slighly different valving spec in the Ohlins front end 750. I will report in the other thread when I get the forks back. Give RT a holler regarding the modified stock cartridges, Kendog. You know you want to...

[Robert Taylor]

There are distinctions here,

1) Spring rate according to rider weight / height and how much weight has been pared off the bike for racing. The standard springs in the 750 are 10s and that suits most riders 75 - 80 kilos up to about 90 - 95 kilos, dependent on how early the throttle is opened and for how long.

2) 0ils with bigger centistroke numbers ( thicker viscosity, the sae ratings on bottles are roughly indicative only ) will flow less fast through the bypass bleeds but have very little effect when the shim stacks open.

3) Racers in fact require relatively fast rebound characteristic because they are arriving at the next bump a whole lot sooner, requiring quick recovery. Road and track day riders require slower rebound because of their slower forward velocity.

4 ) Tuning by viscosity with a modern shim stack cartridge is not really the correct way. Moreover, if you instal a thicker oil to ''tune'' rebound ( we are talking about cartridges, not damper rods ) it will make the low speed compression feel firmer. That is not always desirable.

The mod has corrected a very real problem with the latest k7 and onwards forks, LACK OF HIGH SPEED rebound due to a very soft shim stack. By incrementally and subtley firming up that stack it has also allowed the installation of a thinner viscosity oil, allowing more low speed compliance and ALSO allowing the rebound clicker to a position that allows adequate low speed flow.

There is ALWAYS a very fine window of position where the clickers should be set. If they are close to being maxed out inwards or outwards then you are compensating for a valving spec that is not suitable, FACT.

Inm the end event it is always a choice between a cheap fix or one that will work better

I thought it timely to bring this up again because we have recently done a lot of dyno work with 20mm fork cartridges. With these particular Showa type forks they use a bending shim stack mid valve, the paricular mix of components is also used in the current model CBR600RR. This technology works very well but as JD has correctly pointed out elsewhere you have to be very careful about pressure balance. Get it wrong and the forks readily cavitate, that means the pistons are passing through ''froth'' and there is no damping / delayed damping.
The K6 on GSXR600/750 is notorious for woefully fast high speed rebound damping and as we discovered today on our dyno so is the CBR600RR. The instinct of the rider/tuner is to close in the rebound clicker to as little as only 1/4 to 1/2 turn out to give it more return control. That delivers at least three very negative by products 1) you may get an increase in high speed rebound damping but you also get more low speed damping which you very definitely do not want 2) As the rebound bypass cross talks / flows both ways you also get an appreciable increase in compression damping which again you do not want 3) The forks cavitate like mad with very very pronounced hysterisis / damping delay.You not only see this on a dyno, you feel it when you bleed the fork and it just feels horrible on the road / track. It also screws tyres. ( 25mm cartridges are a lot less susceptible and more ''forgiving'' re this issue )
The only soultion is to revalve the cartridges so that the high speed rebound damping provides the appropriate amount of damping force and also allows the rebound clicker to operate within a window of around 2 to 2 and 1/2 turns out to prevent this hysterisis problem.
''Fully adjustable suspension'' ( via external clickers ) is as big a lie as ''I didnt sleep with that woman''

[JD Racing]

A good informative post Robert, the external adjusters are also partially disabled by the increasing use by manufacturers of bleed holes in the pistons, the cavitation you see is visible witha crank dyno, imagine what it would be like if you could spike them as in real use with an EMA dyno.

[Robert Taylor]

A good informative post Robert, the external adjusters are also partially disabled by the increasing use by manufacturers of bleed holes in the pistons, the cavitation you see is visible witha crank dyno, imagine what it would be like if you could spike them as in real use with an EMA dyno.

Yes Id love an electromagnetic or a hydraulic dyno but the market here is just not big enough to justify spending telephone numbers on such a piece of equipment. I hear what you are saying, indeed when you are hand bleeding the rods you can hand dyno / spike it to feel for cavitation. Its also interesting to evidence the variations in bleed hole sizes / slots for different makes and models.
The average owner / rider would be horrified to realise just how ineffective those ''fully adjustable'' ( bollocks! ) clickers are and how easy it is to introduce cavitation. There is so much deliberate misinformation out there it is unbelievable.

[Pussy]

I've just been communicating with another KBer regarding this mod.
One of the symptoms of the stock shortcomings is a feeling of "vagueness" from the front when the forks become "unloaded" rapidly (say over a brow, or off camber or rapid change of direction), and a pattering effect on corrugated corners. These are caused, in MY opinion, by the weak high speed rebound.
The "Gassit Girl" mod fixes it! It is the same mod that Toot Toot had done to his K8 sem fiddy

[dipshit]

"vagueness" is putting it mildly. Felt like the front momentarily lost traction.!

[Shaun]

"vagueness" is putting it mildly. Felt like the front momentarily lost traction.!


You got it in one

[Pussy]

"vagueness" is putting it mildly. Felt like the front momentarily lost traction.!
The above mod puts decent oil in the forks, too, dipshit.
We have found the 15 centistoke oil works great for a road application

[dipshit]

Well dropped my forks out and sent them off to RT last week for this mod.

...Holy crap! I wasn't expecting this much difference in the feel of the bike after putting them back in!

The 600 steers and holds its line so much better now.

Before sometimes the 600 would feel like it wanted to run wide if you weren't fully on the game or was going through a corner on a trailing or neutral throttle. Gassing it mid-corner would suddenly tighten its line.

But now after sending the forks off to CKT the 600 is transformed!

Responds and goes exactly where you point it and holds its line no matter what you do with the throttle. Exactly how I like it.

I wasn't expecting this relatively simple fork re-valve to address those issues. I thought that's just the way the bike is and/or was my lack of riding skills for a modern performance based bike.

Very pleased with the handling and the feel of the ride of my GSXR now.

[Pussy]

Good one, dipshit.... I knew you'd be rapt!
Amazing, eh, how such a relatively inexpensive mod and some decent oil can make such a difference.
Annie is still VERY happy with the way the forks on her sem fiddy perform.
I've still got the "leave the bloody things alone" mandate to adhere to!

[dipshit]

Amazing, eh, how such a relatively inexpensive mod and some decent oil can make such a difference.

Hell yeah.

I got the 600 with the idea of making a sweet handling bike.

Two bikes I had ridden in the past really made quite an impression on me because of the way they handled.

An RZ 350 that had lots of suspension work done on it. It was very easy to change direction on yet still very stable and sure footed. Great fun to ride!

And a friend's 998 S. Point it in any direction and it would hold its line, bumps or not. Sweet.

Now my 600 starting to feel like this.


:niceone:

[dipshit]

Anywho... so how dependent is this rebound fork mod on the 5 wt Ohlins oil..???

If I was to get a fork oil change, would any 7.5 wt fork oil be still be within working range?

[Shaun]

Anywho... so how dependent is this rebound fork mod on the 5 wt Ohlins oil..???

If I was to get a fork oil change, would any 7.5 wt fork oil be still be within working range?


No mate, Ohlin's is best and consistent

[dipshit]

No mate, Ohlin's is best and consistent


Bugger, that was a waste of $160. I hate it when mechanics don't do what you ask... and they think they know best. :crybaby:

[Shaun]

Bugger, that was a waste of $160. I hate it when mechanics don't do what you ask... and they think they know best. :crybaby:



ASk for your money back then dude, IF you asked for Ohlin;s Oil?



also, Don't ask the internet and so called knolegable people mate, email Robert at CKT direct for a factual awnser

[Robert Taylor]

Different brands of oil all too often react against one another. Unless you start with completely dry components, INCLUDING cartridge strip two differing brands of oil can often end up creating a gummy sludge. We have seen this time and time. Its surprising how much oil a cartridge still retains, as well as that trapped inbetween the inner and outer sliders

[dipshit]

I had rung the motorcycle shop a week ago to sound them out (the mechanic was supposedly one of the better suspension guys in the south island) and told him that the forks have had a re-valve from CKT/Robert Taylor and did he have or could get Ohlins fork oil for a strip and clean and new oil.

I then asked the workshop foreman again in the morning when I dropped the bike off if they had Ohlins oil - "Oh yes"... though I din't ask the mechanic who was doing the job, but he was the guy I had talked to the week earlier. And with the CKT Ohlins sticker on the forks and Ohlins shock on the back... you would of thought. :facepalm:

But no, when it came time to pick the bike up... Ohlins oil... phfff, oil is oil... it will be fine... :brick:

from the job card and what he told me, it has some Motul Expert 7.5w oil in them now.

Will this be ok till next winter, or would they need a strip and new Ohlins oil again?

[Robert Taylor]

I had rung the motorcycle shop a week ago to sound them out (the mechanic was supposedly one of the better suspension guys in the south island) and told him that the forks have had a re-valve from CKT/Robert Taylor and did he have or could get Ohlins fork oil for a strip and clean and new oil.

I then asked the workshop foreman again in the morning when I dropped the bike off if they had Ohlins oil - "Oh yes"... though I din't ask the mechanic who was doing the job, but he was the guy I had talked to the week earlier. And with the CKT Ohlins sticker on the forks and Ohlins shock on the back... you would of thought. :facepalm:

But no, when it came time to pick the bike up... Ohlins oil... phfff, oil is oil... it will be fine... :brick:

from the job card and what he told me, it has some Motul Expert 7.5w oil in them now.

Will this be ok till next winter, or would they need a strip and new Ohlins oil again?

Some oils dont react, impossible to say if the Motul will react with the vestiges of Ohlins oil that will have still been in the forks. On its own its in fairness an excellent oil. To not put too fine a point on it there is a lot of misunderstanding or should I say total ambivalence to this issue where differing brands of oil can react against one another. Out of sight out of mind.....