Front Fork Fixes

[Moto]

After reading all of the old posts related to various discussions about the midvalve problem with the 426 forks, I am curious first of all to find out if DaveJ has yet to achieve that elusive "fork nirvana". I'm interested to hear if you have been able to make your fork rebuilds last any longer than 40 hours. I would certainly appreciate a run down of your final settings, including what parts worked and the best place to find them, ect. I know that Scott F also has a lot of knowledge in this area. What advise would either of you or any of the other knowledgeable individuals in the group give to someone that has finally mustered up the nerve to actually try messing around with the shim stack? I am curious about what effect altering the shim stack and adding bottoming cones has on the different parts of the fork stroke. I'm also curious if people riding in all conditions could benefit from, for example, removing one or two shims from the high speed circuit or is it more of a subjective matter? I would certainly appreciate some mentoring in this area and I'm sure that that others in our group could benefit from the information as well. Thanks!

[DaveJ]

Moto,

The real trick to this whole thing is to understand that no single fork set-up will provide the best ride under all conditions.

The set-ups I use for general trail use is very different than what I think is best for the big tracks. And if I was just as serious about FMX, I may have a third consideration.

In either case, and to no surprise, it really comes down to time and money. In general, the more you have, the better the ride.

If you use the bike solely for track use, some minor adjustements to the stack may suit your needs. Bottoming cones will aid with the comfort of the occasional hard hit.

For trail use, the rider will suffer from too much high compression, which I feel cannot be resolved with changes to the main valve stack since this is an issue of the mid-valve. But then if you remove the mid-valve, the factory seal head seems to get over stresssed (I think).

Therefore, bottoming cones then serve two purposes. They remove the seal head valving stack, and they provide a cush bottom end.

So the bottom line is to determine what you plan on doing with the bike. Then decide how much time you want to spend making changes. Then how much money you want to throw into all of this. And of course, if you want to do the work or select from the various shops with someone that will set it up to suit your needs.

Hope that makes some sense.

DaveJ

[cfisher185]

If you decision end up being having the fork revalved I would like to make a suggestion. Try calling MX-Tech East Coast Suspension. I have recently had my forks revalved by then and they did an unbelievable job. I race motocross and HS and my forks work perfect in both with a few clicks to transition between. They fixed the mid-valve problem without risky the rebuild life span. My forks go about 60hrs before needing rebuilds now. Its not cheap - $299 (final cost after shipping) but it is worth every penny. I am not sending my suspension anywhere else when I get machines in the future. They were professional and friendly and I was given a Home, Business, and Cell phone number when I received my forks in order to contact them even on Saturday / Sunday for dial in help. Though no setup help was needed - they worked perfect as delivered. Anyway the whole package was above average, the product, people, and service were spectacular. Just thought I'd add my $.02 ...

[Scott_F]

Moto, if you have never worked on forks before, I suggest you educate yourself before diving in. It is too easy to ruin very expensive parts. Right DaveJ? ?

You can learn from a suspension tuner or video tapes.

[DaveJ]

Scott has made a good point. Anytime you tear into this stuff you risk the chance of making many mistakes, and some can be costly.

During my initial quest, I didn't have much luck with the suspension shops and that too was a bit costly.

However, if you can find a good one, it's worth the money. Sounds like MX-Tech may be just that.

By the way, don't ever assume that what I post is the only way of doing something. My process for engineering these forks was trial and error. I don't know if it was luck or persistence, but I'll have to assume there are more sophisticated ways of getting to what I concluded.

DaveJ

[Moto]

I appreciate the advice.

DaveJ, I can relate to your comment about time and money, this seems to be the way that everything mechanical works. It is not an issue of cubic inches, but one of cubic dollars. I’m wondering if you could give us all some approximates of the time and money that your forks have been lucky enough to receive during each new stage of development? Personally, this could give me a better idea if I can afford “fork nirvana”.

My reason for the post was to obviously flush a little more information out into the forum (like Boit was trying to do in a post on 5/16/01) and to get a feel for how difficult it is to make different modifications to the YZ forks for individuals of varying mechanical abilities. Never personally having the guts to do anything other than seal replacements and oil changes on front forks, my curiosity about the subject is growing none the less. I have plenty of experience dirtying my hands in the internals of a thumper engine, but beyond basic maintenance, I have no knowledge about the modification side of the ball game.

Thanks again.

[Scott_F]

Moto, you might not go too far wrong if you buy a Race Tech Gold Valve kit. I think they still come with a video and good instructions, so it will give you a good starting point.

[DaveJ]

Moto,

I guess I should begin with my usual disclaimers.

First, there's no right or wrong way of doing this stuff. So take what I say as a recommendation, but not gospel. Ask around.

Secondly, sometimes big changes do little, and little changes make big differences. Even one or two compression clicks can make the machine handle very differently. Proceed wisely.

Third - no one fork will ideally work for all conditions. The forks I have now are within a few clicks and turns for 90% of my riding, except SuperCross. My ideal SuperCross fork would most likely use a mid-valve.

Lastly, sometimes "fork problems", are rear end problems. Meaning, you had better make sure the rest of the bike is probably dialed before you start wasting time and money on resolving the forks.

Okay, one more. In general, the faster you go, the tighter the fork. Which means what works on one part of the track, may not be best for other parts of the track. Decide on what mods yeild the lowest overall track times...if that's your thing.

Onward.

The first and easiest modification are changes to the compression stack. Yamaha shipped the bike with what's called a two-stage stack. About 40 or so shims are stacked together, in two primary groups. The top is the first stage, or low speed, the bottom is the high speed. Vary at will, keep notes. These mods can be done with the proper 14mm allen driver and impact gun. The fork simply needs to be turned up side down. About 30 minutes total time when you get good at it. Expect an hour or two for the first get go since you have to grind the top of the nut peen off. A minor process.

The next level, would be to replace the entire valve assembly with what's often called an "Ultra Adjuster". These allow both external adjustments of high and low speed. The more you pay, the more incremental the adjustments. Many in the suspension world seem to shun these since true suspension tuners would never vary from the science of making changes to the stack. It’s true that you could probably provide a finer tune via the shims, but when a quick change is needed, they are great to have. I personally recommend these.

At this point I would pause, drink a beer, and take a moment to consider if the next stage of modifications are what you really want to get into.

These involve breaking the forks apart to the lowest level, which means opening the cartridge tubes. This involves drilling and grinding around delicate parts. Slip or drill too far, and you’re quickly in the hole for $200 to $500 each fork. Even a slight ding on the compression rods and your in the hole…deep.

If you so choose, the addition of bottoming cones are a good one. But if you only ride trails, forget it. If you are jumping the bike, they will more than pay for themselves in the cost of medical bills. I have over shoot or cased some jumps I should not have walked away from. What a difference an extra inch or two makes when it come to bodily harm.

These sell from $150 to $250. If you have done them before, you could complete this job in about 4 hours. Perhaps less. First time out, about 8 to 16 hours if you have the right tools on hand.

Once you have entered the realm of the cartridge tube, you now have access to the rebound stack and that infamous mid-valve. What you can’t do, is remove the mid-valve without making a change to the factory seal head. Bottoming cones are one form of a change, a restrictor plate is another. Or do like I did and use a combination of both. One of the other evils is to lesson the stack on the mid-valve. You can add shims, but that’s about it.

And once upon a time, KYB use to sell a collection of pistons for use in the cartridge tube. Now they don’t. Perhaps someone out there is making or could make these. This too would be a consideration to replacing or removing the mid-valve.

My take, unless you’re a pro SuperCrosser, (and I mean “Pro”) is to remove it and run a restrictor plate. However, if you keep the mid-valve, you could probably dial out a lot of high-speed harshness with the ultra-adjusters.

The combo of bottom cones, ultra-adjusters, and mid-valve installed is a good one.

Lastly, for another $50 to $200 per fork tube, you can have them treated with titanium nitride. This is the “gold” color you’ll see on many road bikes, but now less and less on off road machines. Seems to be that many shops had a hard time finding a good margin with a facility that could prep and deliver the work with little or no imperfections. Some considerations have to be given to the changes in the properties of the metal as well. Keep in mind this is not a coating and the only enhancement other than looking cool is less friction between seal and tubes. Oh, and it makes the surface harder.

The only other thing to add to this list is oil. As with most things, usually higher cost yield better results, but does not guarantee it. I’ve been through about four types of oils, the best being KYB 01 from ENZO Racing. $11 to $17 per quart. Seems to be the stuff of unspoken secrets. And check the fork level often, since this stuff seems to disappear…somewhere.

That’s about it.

If you have detailed questions, let me know. Scott F., DaveS, and I’m sure many others can also provide some great inputs to this as well.

Or, save yourself the pain and just take your forks to those MX-Tech guys.

Best of luck!

DaveJ

[This message has been edited by DaveJ (edited 07-30-2001).]