Fork Spring preload

clw · Dec 20, 2002

2002 YZ250N I think this stiff chassis may benefit from less preload on the forks. Its static sag is just over an inch (28mm) and it transmits the trail trash to my hands.

Questions:
The manual shows washers to add, but no way to reduce, can the preload be reduced?

What's the key to getting less input to my hands on this stiff beast. Once it's in the stroke it's OK, but the initial sharp hit is painful. Can this chassis be beat? It has been revalved twice.

russ17 · Dec 20, 2002

First I would say contact the person or company that you had the revalve done.Explain to them what the bike is doing and where it is happening on the track or coarse ect. Your tunner should be able to go by the information that you give them and make it right.I also know alot of riders that say that they are a B rider and truthfully they are a honest C- rider. It will only benifit the rider to be honest with themselves on the level that they ride. This is just a general statement and not directed at you. I have spent countless hours on the YZs for my personal use and I believe that they can be tammed

marcusgunby · Dec 20, 2002

To reduce preload you often have to machine the top washer to allow the spring to drop into the cap-im not sure you can do this on the bumper forks.The only way i can think of is to buy shorter springs, also i really dont think a small change in preload is going to make your problem go away-i havnt done any work on the late yzs but i know a few have had problems getting them plush-sorry i dont have the answer.

clw · Dec 20, 2002

Thanks Russ and Marcus:
I hope it's not a problem with my ability, I do ride the A class but told him to valve for an older A (that's me) or a younger B. I spoke at lenghth with him this AM. His suggestions were to be sure the forks aren't binding and to increase the sag a little (to transfer a little more weight to the rear). When I compared the lack of plushness to the WP43's he said that's a given, the new Yammys are stiff. At slow speeds it feels very overdamped, almost like the forks resist motion, this isn't felt when standing next to the bike pushing down on the forks though.

When asked he said that he used a 12mm clamping shim. Would it be appropriate to drop the claming shim to an 11 and add a 1mm larger shim in the 2nd position off the piston? Just a thought. I'm getting close to just doing it myself like I did with the Gas Gas.

russ17 · Dec 21, 2002

C/W- the clamping shim plays a big part, I would also ask if he made any mid-valve changes.

clw · Dec 21, 2002

Russ:
Asked and answered-no mid-vavle changes. Commented on how he likes the YZ mid and mods the KX mid to be like a YZ. He said all changes were made at the base valve.

Marcus:
Machining doesn't sound very practical. 3mm or so gained probably wouldn't be noticed.
So this stiffness is a common complaint! I saw in one of the new mags that one of YZ's 2003 improvements was adding more flex into the chassis.

marcusgunby · Dec 21, 2002

clw the stiffness is a common complaint-im not totally convinced these forks wont work well when modded as most things can-its a case of spending enough time developing setting.I would whip the base valves out and fit the 11mm clamp shim with no other changes-it will reduce the whole stack stiffness and it would be interesting to hear the results.

clw · Dec 21, 2002

Thanks Marcus; After dredging around on this and other forums for the last hour I think I'll do as you suggest with the 11 and if I need to take more off either remove or go down in diameter on the large shim on the HS stack. Probably won't be able to acquire the shims till next week. The KYB's are 8mm and my stock of 6mm's are for the WP.

russ17 · Dec 21, 2002

clw I agree with marcus. Very interesting on his aproach on the KX mod mid though. I feel that the relationship between the the active valve and the and the passive is where its at as far as the forks are concerned. ther was some good threads on this on here that opened my eyes to this, even though I had to read it a 100 times. Remember this is just my opinion

clw · Dec 23, 2002

Had an hour or two to burn Sat. PM so I pulled out the base valves of the forks and had a look. No 11mm, so I removed the large HS shim from the stack. Rode yesterday, a very noticeable change in the action, for the better as the sting and choppy feeling was at a reasonable level. Also seemed to help with the Yamaha mid stroke spike.

Questions:
1. Should I have moved this shim to the other side of the crossover instead of pulling it?
2. Changing the clamping shim affects? Pulling the largest HS shim affects? Are both changes similar in results?

marcusgunby · Dec 23, 2002

c/w i have recently had my eyes opened to which shim has what effect.The truth is shims right in the middle of the HS part affect HS and LS about equally.As does the clamp shim for that matter-its very hard to for example just increase LSC and not effect the HSC.

If your forks work better then you did the correct thing-no right or wrong as long as it works.

Fork Spring preload

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