81 GPz 550 forks

I recently rebuilt the forks on my 550 GPz, new seals, O ring and 15 fork oil. They still feel very mushy. Don't know if the springs are original. Should I call progressive for new springs? They feel like very light fork oil, but I put 15 in. Any ideas?

What about the fork air system?
How much air pressure are you running in there?
Is each fork leg balanced in amount of air?

I run about 12 psi in my 81 and get firm handling.

If you buy a spring kit from Works, get the 280XH kit. The one they have listed for the 81 gpz550 is wrong. It's too skinny. The spring should be a 28mm, not the 25mm they have listed. When you cut the preload spacer, it must be at least 60mm long, but prefereably 65mm or more if you are heavier than 160 lbs. Then I don't run more than about 5psi or so with 10W30 oil in the summer. The lower pressure should take it easier on the seals too.

By the way, the stock springs are almost always mush by now.

I did call Works. They recomended the 250X springs. How did you decide that the 280XH springs were better?

cpgpz wrote:

I did call Works. They recomended the 250X springs. How did you decide that the 280XH springs were better?

I bought the 250XH. The outer diameter is 25mm (nominal, they are actually around 24mm). The stock ones that came out are 28mm (actually 27 or so).

I then had to re-order the 280XH kit.
(With the 280XH kit, the preload needs to be cut no less than 60mm, but I found 65 to be better.)

Been through this twice with them, actually. The second time, recently, I told my friend who just bought an '81 550 gpz to get the 280 kit. Works talked him into the 250 kit, so back it went. It took two weeks to get the 280 kit. My friend had to argue to have them pay for the shipping.

You don't have to trust me, take out a stock spring and measure the diameter. It will be between 26 and 28 mm. The 250 kit will be between 23 and 25mm. The 280 kit will be between 26 and 28mm just like stock. I think a 28mm spring should be replaced with a 28mm spring. Maybe they disagree, but I don't like the idea of the spring zig-zagging inside the tube.


By the way, this info is for the 1981 KZ550 D (gpz) only. Other years had different forks.
I have about 7 or 8 pairs of '81 gpz 550 forks. They are all the same.

And, I really do love the Works kit. I haven't compared it with other brands, but they do exactly what I wanted. The laden sag, unladen sag, and bottoming force are just about perfect, especially when used with Works shocks in back (stock is way too mushy). BTW, Works has the wrong dimensions for the rear also. I had to talk with one of their techs and send him geometric measurements of the rear suspension so they could custom make some shocks for me. They don't charge extra for that and they will adjust the springs etc for free if it is wrong. They are a very good company, but during the busy (racing) season they are slower to respond.

I don't know why their info on the 81 gpz is wrong, though. Maybe they are mixed up with another model.

Post edited by: loudhvx, at: 2006/10/14 21:36