GSX-R 600/750 K6/7 Fork mod

**Pussy** · 6th December 2007, 09:39

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** · 6th December 2007, 11:52

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

)

**Pussy** · 7th December 2007, 07:30

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** · 8th December 2007, 11:41

#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** · 8th December 2007, 15:38

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** · 8th December 2007, 15:42

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** · 10th December 2007, 09:33

Originally Posted by Robert Taylor

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** · 10th December 2007, 12:19

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** · 10th December 2007, 12:25

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** · 10th December 2007, 16:43

Originally Posted by 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

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** · 10th December 2007, 16:46

Originally Posted by Shaun

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** · 15th December 2007, 13:53

Originally Posted by Robert Taylor

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** · 23rd December 2007, 22:41

Originally Posted by Pussy

...
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** · 24th December 2007, 06:32

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