Two Stroke Motocross
Two Stroke Motocross Forum => Technical => Topic started by: Stusmoke on December 28, 2012, 05:23:55 AM
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G'day all.
I've been spending a fair wad of time out in the shed lately trying desperately, without success thus far, to eliminate the godbloodyawful harshness of my 2001 CR125 Kayaba forks.
I was initially getting severe headshake and front end wiggle so violent under hard acceleration that it was grossly dangerous. The fixes below have somewhat lessened my woes, but its still pretty crap.
Things I've tried: I've bled the forks, and replaced the oil to acceptable specs. I've taken out 27 ccs of oil, I've slowed down the rebound and softened up the compression. I've done everything I could think of but its still quite crap. Better, but still pretty crap.
Best I can discern, they are the factory fork springs (.43). No marks on them that I can see.
Thanks for your time,
Stu
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How much do you weight?
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fully kitted I hit the scales at 90. Thats what I wear when riding anyway.
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Two questions: 1. Are the forks even with the top clamp? 2. Have you made any adjustments to the rear shock (rear sag, rebound, compression, etc)? 3. What is the condition of your steering stem bearings (lubed and free moving, especially the lower bearing)?
The reason I ask is if the forks are even with the top clamp and reducing sag should help tame down the head shake. Also, if the lower bearing is frozen, rusted up, it can affect the head shake as well. I would suggest making only one change at a time, forks first, to see what had the most effect.
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Stock springs settings are for a rider of 80kg according to racetechs calc.
If the 90 you weight are kg I reckon you don't have stock springs or the forks internals are dirty.
Best is to start at the rear shock and linkage. If the linkage is not well maintained all bets a re off anyway.
That alone could be the reason for harshness although more at the rear.
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Ive always been impressed by how well the rear soaks up small hits, big hits and miniscule bumps. I checked all the bearings when I first got it, but I'll run over it again anyway. I'll also try reducing the sag and getting the forks flush with the clamps.
Cheers guys, I really appreciate it.
I'll report back soon.
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Have you checked the tension on the clamps, if they are overtightened (check your manual for torque settings) it will cause the internals to bind up. Get a tension wrench onto the bolts, you will be suprised at how loose it is.
Second thing to check is your front axle, the way you put your front wheel on can also cause forks to bind.
I'm not to familiar with that year forks, but always spin the front wheel and grab a handful of front brake (to center the disc) and pump your forks up and down a couple of times before tightening the clamps on the axle lugs at the bottom of your forks.
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Have you checked the tension on the clamps, if they are overtightened (check your manual for torque settings) it will cause the internals to bind up. Get a tension wrench onto the bolts, you will be suprised at how loose it is.
Second thing to check is your front axle, the way you put your front wheel on can also cause forks to bind.
I'm not to familiar with that year forks, but always spin the front wheel and grab a handful of front brake (to center the disc) and pump your forks up and down a couple of times before tightening the clamps on the axle lugs at the bottom of your forks.
Interesting, I'll do all of the above. Cheers.
I also made a fair bit of progress. I dug my manual out of a pile of random junk and set everything back to bone stock. Worked my way back to a more of a trampoline setting rather than a jackhammer. Its still not good, but its much better. Had arm pump so so so bad in less than a minute before.
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Do you grip your bike with your legs? That could reduce arm pump if not eliminate it.
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Do you grip your bike with your legs? That could reduce arm pump if not eliminate it.
I've always said that motocross makes you work muscles you never knew you had. I'm always hanging on with every muscle that can be used to hang on. The armpump I was getting was mainly because of the insane feedback I was getting from the forks. My muscles went tingly and numb inside 5 minutes. It sucked.
I missed out your comment on the spring rate sorry. I've looked and looked and looked but best I can see there is no discernible marks on the spring.
Thanks
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Yeap I hear you, gripping the bike with the leg makes it easier to be loose on the handlebar. But to grip the bike is not something coming easy really.
I have a bike with a bit harder springs and get no arm pump. I'm in the middle of the YZ250 ('09)rider weight max. 65kg and the RM250 ('08)with YZ250 engine rider max weight 85kg. The softer bike is still better IMO I ride off road, most open area and a few single trails.
I use ATF D3 in my forks and change that oil every 40 Hours but I think to go to 20 hours for the fork oil change it is worth it.
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Listen friend, you've got several good tips already, but let me suggest something real simple. Tighten the nut on your steering stem. My boy was having sever head shake on his '01 CR125R, and we cured it in about 10 seconds by tightening the steering stem nut. I may get flamed because we didn't torque it according to the book, but the front end is still plenty loose, and he hasn't had a bit of headshake since. Good luck!
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I guess his way would work, but that's not very nice to the bearings. A steering stabilizer effectively does the same thing but better. As for arm pump, don't grab the bars with all your strength. I'm running the same crappy 46mm KYB's as well and they do indeed blow, no real way of fixing it unless you do a revalve. Apparently you can get them fairly close to SSS forks with a revalve, I would even go as far as throwing sub chambers on as well.
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Im without money at the moment unfortunately. Even when I do find a job, I'll be saving my money for a 2014 150sx. Depending on the changes that it gets that is. I personally have dreams of DFI..
At any rate, I've relubed the steering stem bearings, and tightened the nut. I'm going for a ride today and will report back.
Thanks guys.
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I would aim for the smart carb and if anything 144 stroker kit. And believe it or not your CR can be cleaned up to the point where it is on par with the KTM. That's lame some what cool side of two strokes from the last decade, nothing really has changed except for suspension, which the later crf stuff should bolt up with little to no issues..
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I would aim for the smart carb and if anything 144 stroker kit. And believe it or not your CR can be cleaned up to the point where it is on par with the KTM. That's lame some what cool side of two strokes from the last decade, nothing really has changed except for suspension, which the later crf stuff should bolt up with little to no issues..
It could be, but its not the best handler in the world. Its good, but not amazing. Thats one thing the KTM is down with. Even if I did spend 3 grand getting it hopped up and good to go, the KTM would still more than likely have many advantages.
Besides, I've always wanted a brand new bike and I'm sick of Hondas and Yamahas. Time for a change.
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Plynn41 has good advise. On any mx bike you should have to push on the bars to move the bars when the bikes on a stand. The bars should stop and not move, when you stop pushing on the bars with your palm on a stand. On 04-07 cr125,s you can run up to 110 mm of sag, most bikes you can run more sag than the book says. I rode a pals 01 cr125, no head shake at all. Alot of riders put there body weight on the bars and not on the pegs. Once you relax and keep your body weight on the pegs, you,ll rip.
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After a fair while of tweaking and trying different combinations of everything suggested here, I've made it MUCH more comfortable. Headshake is gone completely but theres still more harshness in the first inch or so of travel then I would like. Its certainly not BAD though.
Thanks everyone.