GS 1000 with Yamaha YZF R6 RSU fork and GSXR 1st gen wheels

[John Kat]

I had already modified a GS 1000 suspension with a GSXR 1100 2nd gen monoshock swingarm and it's accompanying 43 mm RSU front fork..
This modification brought the bike in the "modern" bike category expected from a cartridge type fork and Ohlins rear shock.
The result however was not ideal as the GSXR 2nd gen fork remains very firm despite using the softest settings available both for compression and rebound.
Looking around for a better RSU type fork, I discovered that Yamaha uses a fully adjustable RSU fork on it's YZF R6 bike.
The dimensions are OK with a length of 750 mm and 43 mm stanchions spaced 210 mm apart.
This is great as worst case one can use the stanchions in the GSXR triple with no modification.
In practice, I discovered this was the only possible option as the R6 triple requires a 30 mm ID top bearing that will not fit a GS 1000.
The good news goes one step further if you want to use the GSXR 1100 first gen 18" wheels!
While you need to machine some adapters to fit the wheel spindle in the front fork, you can reuse the R6 calipers by using ZZR 600 disks.
These are 300 mm in diameter compared to the 298 mm Yamaha OEM's and their 12.5 mm offset puts them about 1 mm closer than the OEM version.
Nothing a small shim behind the calipers can't catch!
The adapters are currently beeing machined and I'll post a picture when done.

[mmattockx]

The result however was not ideal as the GSXR 2nd gen fork remains very firm despite using the softest settings available both for compression and rebound.

Was the fork rebuilt with fresh oil and springs appropriate to your and the bike's weight? How is the sag? You could also change oil to a lighter weight to soften the damping up.


Mark

[John Kat]

Was the fork rebuilt with fresh oil and springs appropriate to your and the bike's weight? How is the sag? You could also change oil to a lighter weight to soften the damping up.


Mark

Yes, I did all of that.
I even looked at the shim stack but stopped short of modifying it...
In any case I'm going from a 1980 to a 2004 design not to mention the calipers and the overall weight!

[steve murdoch]

Looking forward to the pics.

[mmattockx]

Yes, I did all of that.
I even looked at the shim stack but stopped short of modifying it...
In any case I'm going from a 1980 to a 2004 design not to mention the calipers and the overall weight!

I see I misread your OP, I was thinking a later USD fork. Hopefully the R6 fork is a significant improvement for you. Though, if the GSXR fork used shim stack damping I'm not sure you will see that big of a change. I am also looking forward to seeing the finished version.


Mark

[80GS850GBob]

I had already modified a GS 1000 suspension with a GSXR 1100 2nd gen monoshock swingarm and it's accompanying 43 mm RSU front fork..
This modification brought the bike in the "modern" bike category expected from a cartridge type fork and Ohlins rear shock.
The result however was not ideal as the GSXR 2nd gen fork remains very firm despite using the softest settings available both for compression and rebound.
Looking around for a better RSU type fork, I discovered that Yamaha uses a fully adjustable RSU fork on it's YZF R6 bike.
The dimensions are OK with a length of 750 mm and 43 mm stanchions spaced 210 mm apart.
This is great as worst case one can use the stanchions in the GSXR triple with no modification.
In practice, I discovered this was the only possible option as the R6 triple requires a 30 mm ID top bearing that will not fit a GS 1000.
The good news goes one step further if you want to use the GSXR 1100 first gen 18" wheels!
While you need to machine some adapters to fit the wheel spindle in the front fork, you can reuse the R6 calipers by using ZZR 600 disks.
These are 300 mm in diameter compared to the 298 mm Yamaha OEM's and their 12.5 mm offset puts them about 1 mm closer than the OEM version.
Nothing a small shim behind the calipers can't catch!
The adapters are currently beeing machined and I'll post a picture when done.

I'd say the springs were too stiff for your application, but the donor bike should've been lighter in nature than the GS...since the GS is heavier I'd figure she'd be a softer rather than harder ride. Maybe look into softer springs....?
What fork oil weight did you use?
As for the top bearing I'd say try allballs.com for a swap to one that'll fit.

I'd also love to see a pic even if it's current...I've got a '95 gsx-r 1100w front end for my 1000g {still sorting brakes}.

[80GS850GBob]

I'll add this - I'd assume you checked the fork tubes for run out so you know they're not bent....used parts can sometimes have not so easily seen problems.

[John Kat]

I'll add this - I'd assume you checked the fork tubes for run out so you know they're not bent....used parts can sometimes have not so easily seen problems.

I exchanged the fork tubes at one stage but the situation remained almost the same.
In the end, I believe the issue comes from the fact that the fork travel is very small on the GSXR 11 K.
More info here:

http://www.thegsresources.com/_forum/showthread.php?206668-A-modern-fork-upgrade-for-17-18-and-19-quot-wheels/page3

[80GS850GBob]

I exchanged the fork tubes at one stage but the situation remained almost the same.
In the end, I believe the issue comes from the fact that the fork travel is very small on the GSXR 11 K.
More info here:
http://www.thegsresources.com/_forum...t-wheels/page3

Ah, so the heavier current bike, with those gsx-r forks, might very well be bottoming out then....this is why checking sag is important...too much sag and your loosing travel.

[posplayr]

Ah, so the heavier current bike, with those gsx-r forks, might very well be bottoming out then....this is why checking sag is important...too much sag and your loosing travel.

When I was setting up my GSXR 1st gen forks, I rode around on a lot of curve and bouncy roads with the zip-ties on the front forks. That would allow me to keep track of maximum stroke over the course of teh ride. It was also always easy to stop and reset the zip-tie if I wanted to gauge the stroke I was using over a particular section of road.

[80GS850GBob]

When I was setting up my GSXR 1st gen forks, I rode around on a lot of curve and bouncy roads with the zip-ties on the front forks. That would allow me to keep track of maximum stroke over the course of teh ride. It was also always easy to stop and reset the zip-tie if I wanted to gauge the stroke I was using over a particular section of road.

That's a good idea....general sag when sitting is one thing, but overall from use can give a better picture.
...crud, now I'll have to go look up the travel specs on the gsx-r forks I have and compare that to the GS specs....I can't imagine they're too different...

[John Kat]

When I was setting up my GSXR 1st gen forks, I rode around on a lot of curve and bouncy roads with the zip-ties on the front forks. That would allow me to keep track of maximum stroke over the course of teh ride. It was also always easy to stop and reset the zip-tie if I wanted to gauge the stroke I was using over a particular section of road.

My GS 1000 ST is equipped with 1st gen GSXR forks improved with Racetech emulators, a pure delight to ride on bumpy surfaces but not in the "modern" bike category in terms of chassis control.
It's difficult to get the best of both worlds!
The best sofar is my 1100 Kat with Bandit 1st gen forks.

[John Kat]

As for the top bearing I'd say try allballs.com for a swap to one that'll fit.

I'd also love to see a pic even if it's current...I've got a '95 gsx-r 1100w front end for my 1000g {still sorting brakes}.

You are right Allballs has a top triple bearing that will fit!
It's model N° 99-3540-5
This is very good news as the R6 triples will reduce the trail compared to the GSXR 2nd gen triples.
I'll have a look at what needs to be done about the lock stops though.
Another good news is that this bearing allows the use of a Hayabusa front fork...
Update:
The lock stop is no issue: it will only need welding a piece of metal to the frame in front of the lower triple bearing.
A quick calculation of the trail gives for an 18" wheel assuming a 28° rake
T=R*tan(a)-D/cos(a)
Gives for the GSXR triples ( D=32 mm) Trail = 134 mm
And for the R6 triples ( D=40 mm) Trail = 125 mm
Of course a 17" wheel will lower these values.
For the R6 triple it gives 114 mm of trail.
We are still far off the GS/GSX OEM specification with 103 mm trail...
However if one lifts the rear of the bike by 2.5 cm the rake will decrease by 1° and the trail with an 18" wheel now becomes
Trail=118 mm and finally for a 17" front wheel
Trail=108 mm that's not too far away the OEM spec

Here's a picture of the R6 triple tree positionned above the GSXR triple

[thebrandonbeezy]

I just wanna see the bike :/

[John Kat]

I just wanna see the bike :/

Here's my GS 1000 ST with the 1st gen fork and wheels.
It will take some time before you see the new project bike as it will be very special...DSCF7160.jpg