Friday, August 24, 2012

DR650 Front Fork Upgrade: Suzi transformed to Siouxsie...

My new local test ride route - dirt on the way to work: can't beat that!
Just like when you hear about that woman down the road who got the boob job, Suzi has had her front end done, and is feeling much perkier than before! 
The DR has been fabulous off-road and a forgiving platform for me to learn how to ride dirt, crush and all the other obstacles that off-road riding throws up at us.  Forgiving is the word though; her front end was always a little saggy - which is just what you want when you're learning, but as I've got faster and more aggressive, I have bottomed the forks out occasionally.  Not a nice sound, and with an over sized gas tank, it was time to think about the next step.  So I contacted ProCycle and chatted with Michael Graham who specializes in DR's, among other bikes like the KLR and KLX250s.  He asked some questions and got back to me with what he thought would be the best solution for my style of riding.  I ordered a set of stiffer front springs (.55s which are 35% stiffer than stock and linear) and a set of Racetech Cartridge Emulators.  Fork dive under braking was a problem as was bottoming over rough crush at speed.  He also sent 3pints of 10 weight fork oil, new forks seals and custom springs for the emulators in case I found the stockers too stiff.   So a week ago the package arrived with some sketchy instructions. 
So a few days ago I decided to get my hands grimy and start tearing down Suzi's forks.  They were starting to squeak of late, and I worried that a couple of real clangers that I had heard at serious speed over some real bumps had perhaps done some damage.  The Suzuki is amazingly simple to work on and this was no different.  I had the garage floor covered in carnage in no time flat with every sort of bushing, shim, washer, spacer, seal, spring and damper rod known to man laying all over the show.  The shop manual is on line, and thankfully I had saved my copy via pdf and had the laptop running with pictures for help! 
 Some parts are deliberately left out of the picture to avoid overwhelming the viewer...and bringing back the flashbacks...
After removing the front wheel, brake caliper, and forks (quick and easy), the hard part begins - getting into the forks, draining the fork oil, separating the top fork leg from the bottom, catching the various shims,springs etc, and removing the damper rod.  There is an allen key at the base of the fork.  In order to turn this you must stop the damper rod turning inside the fork.  For this you need a special Suzuki "damper rod tool".  In fact it's so special, that, despite looking like a huge allen key with a T grip at the top - something that could be fashioned for mere cents, Suzuki want the princely sum of $75.  Kiss my armpit.  I made a substitute for less than a fiver using a few nuts...
The long hex nut is a 3/4", which measures 28.5mm across in new money.  The damper rod has a female size of 30 mm.  This works without chewing it up.  The 2 other 1/2" nylock nuts are to stop it turning on the 1/2" bolt and to allow me to get a socket around it.  Between the two nylocks is a split washer to add further pressure and to resist turning by the nylocks.  It worked a treat.
Once the damper rods were out, it was over to Ryan's shop (thanks, Ryan!) for the drill press and 6 5/16" holes in each rod with 7/16" centres.  Wow, the drill goes through these things like butter, the hard work was deburring the holes so none of those little metal fragments get into the fork and damage seals.
The bottom of each damper rod needs six holes drilled in them. They already have 4 each, but the diameter needs enlarging to allow for more oil flow up to the emulators.  The emulators sit on top of these and resist oil pressure on the compression stroke.  The emulators are adjustable, so they can open earlier or later, depending on how much resistance to compression you want.  Adjustable forks!  Awesome.
The emulators come with 3-4 turns preload.  I reduced them to 2, but, depending on how they work off road, will increase them if I need to. They are machined to fit right over the top of the damper rods, held there by the springs.  It's a nice fit, but I used the circlip to make sure they are oil tight. 
 The emulators are the gold items at the top.  One is seated on the damper rod.  The spring sitting out of the top can be wound tighter or loser with an allen key.  This does mean if you want to adjust them you must pop the top tube bolt off, pull the spring, grab the emulator, adjust and drop it back in.  About ten minutes, and quite easy.
Mid operation: Suzi deforked, and undergoing surgery for a more pert front end
Getting everything back together was a cinch, except for getting the bushings in.  I had to make a slide for a rubber mallet using pvc pipe as I was very worried about denting or scratching the fork surface where oil seals would be attempting to keep oil in the fork!  After a few hours, I got this right and and the forks came together nicely. 
Next is adding oil and preload.  The aftermarket springs are linear (not progressive like the stockers), and shorter.  I had to enlarge the spacer.  After a lot of reading, I decided to make my spacer two and half inches, giving a half inch preload, rather than the recommended 3/4" preload.  I did this because I got very firm straight rate springs.  If you add more preload, you will make the suspension firm immediately, and the bike will be too stiff for every day commuting.  I also filled the oil to 165mm of the top (6.5inches).  This is where Procycle recommend you start.  More oil makes it more progressive and resists bottoming at the end of the stroke. Less oil will make the fork action feel more linear.  I'm not really sure what I'm doing yet, so I figured it's easier to add oil than remove it (Clem doesn't like the taste - the first time with the straw worked, but...)
Then it was off for a test ride.  I headed over to Ryan's to help with a canopy; he'd done it.  So it was off to my local dirt test track - which I've never been up before, but Clem and Iringo had told me there was a dirt track from the top of our residential neighbourhood to my place of work.  Worth a try.  So I headed up and hooked up with the dirt road.  It was more crush actually, very large jagged crush, but worth a test.  I was very impressed!  The mushiness is gone, the forks are still smooth on the road, but incredibly fast and responsive on the dirt, and seemed to urge me to go faster.  The faster I went, the better they worked.  Now this was only a ten minute test, and I'm certainly not ready to call this a success yet, but first impressions are that it was well worth the time.  The trail itself is fun and challenging and takes me down to Long Lake Road.  Perfect!  It'll be my dirt fix on the way to work every day!
I'm off for a serious date with Siouxsie tomorrow (Saturday) to give her a real work out.  Her front end sits an inch or so higher now, and the sag is history.  Oh, Siouxsie, you're a bad girl...
 Suzi is no more: say hello to Siouxsie with the bodacious front end!

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