Phat Trakka 2 - Front Forks 


I had two pairs of 74 L model forks to choose form.  One pair came from the original bike that started this stream of insanity, and the second pair came from the Gold/Orange parts bike that pushed me deeper into insanity.

OEM 35mm forks are not what would be considered beefy by modern suspension standards, so the trick was going to be how to improve them at moderate cost  and keep the Old Skool look. 


Obviously new fork seals were on the shopping list and a set of Cartridge Emulators sounded like a good idea but at about $150, I wasn't so sure. Someone suggested I look at Mike's XS which is a fantastic source for all Yamaha XS650 parts.  And what, I hear you ask, is the relevance of an XS650.


The answer is that they are old bikes, Mike has a huge range of parts for them, they are probably the most common base for a street tracker and did I mention they have great prices.


I ordered a set of fork oils seals, fork boots/gaiters/bellows and a pair of Cartridge Emulators. they were shipped the next day.


In the picture above left, the one on the right is a Mike's Xs unit and the larger one to the rear is a 35mm from another supplier. As can be seen in the picture obove right, the emulator does not fit neatly inside the top of the damper rod the way it needs to.  What is needed is ana adapter.  I started to sketch out what I wanted and as I made the design simpler, I realized that all I needed was a washer 1.5mm thick with an OD of 24 to 25mm and an appropriate sized hole.


Of course I didn't have one washer in exactly that size, let alone two, but after some digging around I found two that had the correct OD and thickness and a smaller ID.  So out came the trusty Dremmel and five minutes later they were good to go.



Before the legs were re-assembled, I decided to alter the rebound damping as well. There was an article published many years ago that recommends blocking off one of the holes in the damper rod, so that's what I did.  It's simple fast and in theory at least should improve, or at least increase, rebound damping force aignificantly.


All the parts were carefully cleaned up and oiled before assembly and new seals were installed in the legs with an extra washer from Mike's XS.


When the bike is more complete and on its feet, I'll splash out for a bottle of 15W fork oil and see how that feels.  I suspect that the suspension will take a bit of setting up.

UPDATE (Sep 13, 2009)

The forks felt just fine individually, so onto the bike they went.  I added 160-170mm of 20W Spectro fork oil and pumped them to remove bubbles etc then set the oil level at 416mm with legs fully extended.  The springs had slightly more pre-load than stock but nothing out of bounds. As soon as the wheel and brakes were fitted, I tested teh front end and it's as stiff as a 15 year old boy staring at MotoGP umbrella girls.


The forks are way too stiff and hardly compress at all.  That's odd, because each leg felt fine before I installed them. The pinch bolts were loosened just in case the legs were binding, but that made no difference. Maybe it's becuase the s[rings are designed to handle a stock heavy bike and this one is lean and light, so I jumped on teh fron tbrakes and it probably sank 1mm.  That's a little short of teh static sag number we neeed, so something isn't right.


Rather than just cutting the stock springs to reduce pre-load, I ordered a set of Progressive Suspension #11-1120 double rate springs.  They are 500mm long versus OEM springs which are approximately 550mm long and they come with a pair of 50mm PVC tube spacers.


Then I started to think about what was happening, and realized that I had probably outsmarted myself.  What I suspect is that the Cartridge Emulator is sitting too close to teh damper rod and I suspect that oil is having a hard time passing through the emulators.  if that is teh issue, then the fix is simple enough - get a pair of risers, say 10mm tall to allow the oil to pass through the emulators and let them do what they are supposed to do.


The plan now is to lengthen the damper rods by 15mm to increase fork travel, fit adapters between the damper rods and emulators and optimize the oil level.


UPDATE (Sep 18, 2009)

last night I drained the oil out of the forks and that changed the front end from solid to stock mushy. That was a simple way to prove that we effectively had hydraulic lock.  So now we need to order and install a pair of spacers to raise the emulators.



Forks Page2  dress up