Monday, October 28, 2013

Lowering Conventional Forks - The Art Of Height Reduction.

I'll be honest... I looked up how to do this on the internet, and what a simple idea!

One pair of standard length, conventional forks.

Here's why.
The GSX750ES has a clip-on style handlebar with one major issue - it's mounted above the top yoke/triple clamp. If you're going to lose this awful looking tiller, you're left with about 30mm of stanchion stuck above the yoke. This, in itself, looks crap. I've seen lowered cafe racers with that done to them, but it's not really the look I want.
So I need to shorten the forks themselves. Now apparently you can get shortened stanchions from someone in the States, but that'll no doubt prove expensive and probably come with its own set of problems. But by fitting a spacer inside the forks themselves, you can actually reduce the working range of the forks. You'll need to cut the main spring too, but then the fork can be dropped through the clamps, maintaining the bike's original height if need be, and cleaning up the top yoke area.

Here's how.
First, strip the forks. Make a start by slackening the top nut/preload adjuster. I used an airgun to cheat/make it easy. If you're taking them out of the bike first, slacken the top clamps only, and use a tight fitting socket to undo the nut. The lower clamp will prevent the fork from turning.

I then removed the four bolts holding the anti-dive unit on to the bottom of the fork leg. That way I can drain all the oil quickly - strewth, what a state! These forks haven't seen a service in years, maybe never.

This is the back of the ant-dive unit. That'll be stripped, cleaned and checked in another post.

With the dust cover already removed, the circlip is now visible above the washer and oil seal. A right-angled circlip pliers makes this job easy. It's corroded and takes a bit of moving to free up.

The next job is to remove the bottom bolt holding the damper assembly into the bottom of the fork leg. Again I'm cheating. Usually a tool is needed to prevent the damper spinning inside the stanchion while unscrewing the bolt. If you use an airgun, it will normally whip it out before the damper has chance to turn. Happy days.

Next I grab the stanchion and pull it up hard against the seal. It takes a few smacks, but eventually pops up through with the top bush. The seal is now easily removed to reveal the carnage inside. Man, this oil is crappy!

Oil with this amount of metal suspended in it just wears the internals away. Changing it regularly prevents wear, and gives a much better ride.

The damper assembly pulls apart and the rod and top-out spring are removed through the top of the stanchion. Now it's time to degrease every component.

This is the damper rod and top-out spring, and this is what I'm altering. Simply placing a spacer above the spring prevents the fork from extending fully, and fork height is reduced. As luck would have it, a piece removed from the frame is a perfect fit on the tube. I cut a couple of pieces just slightly short of the oil bleed holes (don't want to block those). 
Damn, I miss having a lathe sometimes - hacksaw and file it is then.

And that's it!
Reassembly will commence when the sliders have been painted, and I've acquired new stanchions. Watch this space.

Friday, October 11, 2013

Traxxion Dynamics' Linear Rate Springs - GSXR1000

Curing the K6 thou's bumpy bits.
Previous posts dealt with the suspension upgrades on the trusty '06 Gixer. The shock was re-shimmed, serviced and fitted with a linear rate spring. No problems there (with my limited ability at least). The 43mm Kayabas were re-shimmed and filled with fresh oil but, due to funding, came back with the standard 0.95kg progressive springs.
As the months progressed, they started to leak oil and preload adjusters were screwed right in to try and prevent bottoming out. The front was getting very harsh to say the least. Put up against modern bikes and she was beginning to show her age. Smooth roads were fine, but the bumpy stuff was iffy, sometimes scary.

A couple of emails to Traxxion Dynamics and they sorted me out with their straight-rate springs with an overall rating of 0.975kg. I just had to choose the fitting method for the type of spring - either cut the spacer, or alter the top-out springs within the cartridge. I decided to leave the cartridges alone and just cut the spacer.

Forks were stripped as per, leaving cartridges in place, then the old seals were taken out and plenty of brake cleaner inside the outer fork tubes to remove the dirty residue. Photos are limited unfortunately - I got carried away with the job and forgot to take enough of them!

Spring compressed ready for the fork top to be removed from the damper rod assembly.

New springs, note the extra length.

Traxxion provide all the instructions on how to measure the amount to be cut away, but they'd already given me the nod that 40mm was the way forward for the Gixer. The picture below shows the 40mm cut off the spacer (left), and new holes drilled in what's left for the spring compressor.

With new oil seals fitted, it was time to refill with oil and put them both back together. I'm running with the Suzuki standard air gap of 101mm. 
(Both forks were leaking, and when I stripped them they had an air gap of 140mm - no wonder they were getting harsh!)
I slipped the forks back into the clamps and refitted the mudguard, wheel and calipers. I only tighten the lower triple clamp bolts once the wheel is in and the suspension bounced up and down a few times. This relieves any tension/twist when fitting the wheel etc. 

Road test time.
I think we're onto something here. I basically just set my compression damping at ten clicks out, rebound at seven clicks and the preload to the first line on the adjusters. 

A blast along some of my favourite roads and I've still got an inch of travel in reserve! What a difference. It feels so much more stable in the bends now which could be as much do with oil level as well as the different geometry. I'll experiment with less compression damping to see if I can get a softer/more plush ride next.

Overall, I'm happy as. No leaks (for now), and the bike's actually easier to ride. A highly recommended mod. If you're not using a zip tie on your stanchions, go get one now. That little plastic tie is a mine of information!