WAY too stiff KYB sss forks - Drain oil inner/outer chamber?

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5/14/2020 1:40 AM
Edited Date/Time: 5/14/2020 2:00 AM

My bike is a 2016 YZ250f. I bought it with 20 hours on it and I was told it is 100% stock (suspension wise) - the forks looked completely new.
I have 40 hours on the bike now and I serviced the fork twice with oil/seals. The forks have always felt EXTREMELY stiff. I compared to other YZ250f's and they are so much plusher and nicer when you stand beside them and press down the forks (and nicer to ride).
I also compared to other 2016's, which aren’t as stiff as mine either. I am almost sure something is wrong.

My oil amounts are exactly as the manual states - I know we all have our preferences, but am sure it is not meant to be this stiff in stock form.
I don’t know if it matters, but for some reason, one of the forks has 29 clicks of rebound while the other only has 23 clicks from in to out.

I am 183 pounds with gear - not the fastest, but definitely not a beginner, but as I said, the bike is noticeably stiffer when I stand beside it compressing the forks, so my weight shouldn’t matter too much when comparing this way.

Things I have tried to make it softer so far:
- Loosening and tightening the axle nut (with a torque wrench of course)
- Aligning the fork legs
- Tightening the brackets to the right torque spec.
- Replacing the springs with ones I KNOW are stock (4.6) - I later found out the ones already in it were stock too.
- Replacing oil (5w suspension oil, "light") in both chambers + new seals
- Bleeding air before every ride

None of this helped, so I began experimenting with oil levels (even though I find it weird that the stock amounts seem to be so far off, when everybody else likes Yamaha’s stock suspension).

I tried taking 30cc of oil out of the outer chamber (through the bottom of the fork). In this part of the fork, the manual states that the extent of adjustment is between 300cc-365cc, so I figured this was the right place to remove oil from to make it feel softer. I initially put in 355cc (following the manual) but then took out 30cc, so there should be 325cc left. This did not help at all, but I left it that way.

Then I tried taking 30cc of oil out of the inner chamber (upper part of the fork, from the chamber with the compression piston in it). This helped a lot, but it is still a little too stiff. The fact that it worked is strange, as I think this is the wrong place to drain oil from.
The manual states 204cc goes in (or a height between 145-147mm) with no extent of adjustment, so I poured the oil back in even though it helped taking it out simply because I thought this was the wrong place to drain oil from - and of course it became WAY to stiff again.

What am I missing? As I understand it there should be exactly 204cc in the inner/upper chamber with no extent of adjustment. And as I understand it, you regulate the oil amount in the outer chamber/bottom end of the fork to control the stiffness.
Why did it work for me to take out 30cc from the upper part as opposed to the lower part of the fork? Can I do any damage by taking 30cc of oil out from the inner/upper chamber again? It worked pretty good - I am think about taking out a little more than I did last time.

I am desperate to understand what is wrong with my suspension - or with me :-) If anybody would share some wisdom, I would be so grateful, as I live in a country with no dedicated suspension shops (Denmark) and I wanna be able to do all my bike work myself. Thanks in advance!

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5/14/2020 3:15 AM

If you replaced your seals yourself and did not replace your bushings that is most likely your problem. Damage to the Teflon on the bushings during disassembly will cause binding between the sliding tubes making them feel very stiff/harsh. Also using aftermarket seal/bushing parts like Pivot Works, K&S, All Balls, etc... Use only OEM NOK brand or SKF.

The fork with 29 clicks of adjustment id not assembled correctly. The rebound base bold was not screwed all the way onto the damper rod fully before tightening the locking nut so there is a small amount more gap for the rebound adjuster rod to move inside the damper rod causing the extra clicks.

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5/14/2020 4:50 AM
Edited Date/Time: 5/14/2020 4:55 AM

slipdog wrote:

If you replaced your seals yourself and did not replace your bushings that is most likely your problem. Damage to the Teflon on the bushings during disassembly will cause binding between the sliding tubes making them feel very stiff/harsh. Also using aftermarket seal/bushing parts like Pivot Works, K&S, All Balls, etc... Use only OEM NOK brand or SKF.

The fork with 29 clicks of adjustment id not assembled correctly. The rebound base bold was not screwed all the way onto the damper rod fully before tightening the locking nut so there is a small amount more gap for the rebound adjuster rod to move inside the damper rod causing the extra clicks.

Thanks for your input, I appreciate it!

I think you're right about my rebound clicker problem, I probably made a mistake when assembling it!

About the bushings: you could be right, be they dont seem to be worn out to me - and I have had the problem ever since it was almost new, so I am not quite sure about that. I'll wait for some more opinions before I replace what seems to be perfectly fine bushings. Do you have any other suggestions?
Even if they were a little worn, do you think it would make that much of a difference?
I mean, it is EXTREMELY stiff.

Care to take a guess on how long the KYB sss. stock bushings usually last? :-)

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5/14/2020 5:34 AM

slipdog wrote:

If you replaced your seals yourself and did not replace your bushings that is most likely your problem. Damage to the Teflon on the bushings during disassembly will cause binding between the sliding tubes making them feel very stiff/harsh. Also using aftermarket seal/bushing parts like Pivot Works, K&S, All Balls, etc... Use only OEM NOK brand or SKF.

The fork with 29 clicks of adjustment id not assembled correctly. The rebound base bold was not screwed all the way onto the damper rod fully before tightening the locking nut so there is a small amount more gap for the rebound adjuster rod to move inside the damper rod causing the extra clicks.

Loft80 wrote:

Thanks for your input, I appreciate it!

I think you're right about my rebound clicker problem, I probably made a mistake when assembling it!

About the bushings: you could be right, be they dont seem to be worn out to me - and I have had the problem ever since it was almost new, so I am not quite sure about that. I'll wait for some more opinions before I replace what seems to be perfectly fine bushings. Do you have any other suggestions?
Even if they were a little worn, do you think it would make that much of a difference?
I mean, it is EXTREMELY stiff.

Care to take a guess on how long the KYB sss. stock bushings usually last? :-)

I usually get 20 hours. You can get the oem bushing and seal set for 30 bucks.

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5/14/2020 7:32 AM

Don't take any oil out of the inner chamber. It's not adjustable like the outer. It probably felt softer because you had air in there and had less damping.

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Take it to the limit, one more time!

5/14/2020 11:37 AM

5W is also too thick. Use KYB S1 in those forks.

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Braaapin' aint easy.

5/14/2020 1:59 PM

In addition to what slipdog said above, I'd say your main problem is you don't have the inner chambers bled correctly. The first thing is stop thinking of an "amount" that goes in the inner chamber. The amount is irrelevant. What matters is that they are completely filled and bled entirely of any air - and then all excess oil must be drained and removed completely from the upper portion by the base valve assembly before putting the inner chambers back in the fork and reassembling.

The 204cc stated is just an amount to get you started to ensure there is at least enough. Some of this will be removed after properly bleeding the inner cartridge. I would guess you ended up with some of the excess oil in the area at the top by the base valves and were creating a hydraulic-lock condition and/or some of this oil transferred through the weep holes to the outer chamber creating an excessively high oil condition also contributing to a stiff feeling. You'd be best off to have someone who knows what they are doing help you get this right.

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Powerband in every gear !

5/15/2020 4:02 AM

FGR01 wrote:

In addition to what slipdog said above, I'd say your main problem is you don't have the inner chambers bled correctly. The first thing is stop thinking of an "amount" that goes in the inner chamber. The amount is irrelevant. What matters is that they are completely filled and bled entirely of any air - and then all excess oil must be drained and removed completely from the upper portion by the base valve assembly before putting the inner chambers back in the fork and reassembling.

The 204cc stated is just an amount to get you started to ensure there is at least enough. Some of this will be removed after properly bleeding the inner cartridge. I would guess you ended up with some of the excess oil in the area at the top by the base valves and were creating a hydraulic-lock condition and/or some of this oil transferred through the weep holes to the outer chamber creating an excessively high oil condition also contributing to a stiff feeling. You'd be best off to have someone who knows what they are doing help you get this right.

Thanks for the reply!

I think you're right, that makes perfectly good sense.

I am sure there is no air in the inner chamber. I probably did not bleed it correctly, as I intentionally made sure no oil came out through the holes when installed it.

Am I right in assuming that I can just tear it apart, pull out the inner cartridge, turn it upside down and make it go through it's stroke to bleed out any excessive oil (or will it all come out that way?) - and then make sure the right amount of oil is in the outer chamber and make sure it does not hold any excessive oil that the inner cartridge may have bled out? :-)

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5/15/2020 12:58 PM

As someone else said, at 40 hours, replace you inner and outer bushings. Fill the inner chamber, and bleed it correctly, and dump the excess fluid after bleeding. Then put ~325cc oil in the outer chamber. Oh yeah, make sure you fix the rebound clicker issue as well. And lastly, when installing the forks, make sure the axle is not binding, and do not over torque the triple clamps. It is something like 12-14 ft-lbs.

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5/15/2020 1:33 PM

OK, a little update:
I got the rebound clicker issue fixed, so thank you!
I drained the forks completely and started from scratch - filling and bleeding the inner cartridges correctly.
Everything was done exactly as shown in different youtube-guides - and measurements, oil amounts/heights and torque specs completely as stated in the manual. The bushings show no wear at all (and even if they were worn out, I don't think i would make them THIS harsh)
All this makes absolutely no difference at all. They are still way too stiff.
Although I highly doubt it, maybe the previous owner had it revalved? What else could it be?


The only thing that worked for me was to drain 30cc's of oil from the inner cartridge (which I know is the wrong solution)

Just for the experiment, I tried putting in a correctly filled (and bled) inner cartridge into a fork without any oil in the outer chamber - and weirdly, it felt exactly the same. I am really beginning to think something might be wrong.
To me, it feels like a way to high spring rate, but it is the stock one, so not really sure where to go from here.

Thanks to everyone who replied already, I appreciate it!

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5/15/2020 1:51 PM

I would try a lighter spring rate to see if that helps. Unless your not installing the front wheel correctly to avoid binding it seems like you've covered everything apart from valving and lighter springs

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5/15/2020 3:49 PM

What are your clickers set at?

Can you post a picture of your front axle (throttle side)?

You said the main springs were stock spring rate. But what about the inner chamber springs?

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5/15/2020 11:46 PM

garagedog wrote:

What are your clickers set at?

Can you post a picture of your front axle (throttle side)?

You said the main springs were stock spring rate. But what about the inner chamber springs?

My clickers are as MXA recommended for the '16 model:
Comp: 14 clicks out
Rebound: 10 Clicks out

I actually don't know the spring rate of the inner chamber spring, but I was told it is stock.

And yes, will post a picture, but I think it's perfectly aligned.

Thanks for replying!

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5/16/2020 9:28 AM

Should be able to tell if they have been revalved by looking at the nuts for factory staking

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5/16/2020 1:33 PM

Loft80 wrote:

OK, a little update:
I got the rebound clicker issue fixed, so thank you!
I drained the forks completely and started from scratch - filling and bleeding the inner cartridges correctly.
Everything was done exactly as shown in different youtube-guides - and measurements, oil amounts/heights and torque specs completely as stated in the manual. The bushings show no wear at all (and even if they were worn out, I don't think i would make them THIS harsh)
All this makes absolutely no difference at all. They are still way too stiff.
Although I highly doubt it, maybe the previous owner had it revalved? What else could it be?


The only thing that worked for me was to drain 30cc's of oil from the inner cartridge (which I know is the wrong solution)

Just for the experiment, I tried putting in a correctly filled (and bled) inner cartridge into a fork without any oil in the outer chamber - and weirdly, it felt exactly the same. I am really beginning to think something might be wrong.
To me, it feels like a way to high spring rate, but it is the stock one, so not really sure where to go from here.

Thanks to everyone who replied already, I appreciate it!

Even if the bushings still have the Teflon coatings on them, but are rough texture and not silky smoothe the forks will bind. One of many many things I have learned in 30yrs servicing suspension.

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5/18/2020 2:50 AM

Loft80 wrote:

OK, a little update:
I got the rebound clicker issue fixed, so thank you!
I drained the forks completely and started from scratch - filling and bleeding the inner cartridges correctly.
Everything was done exactly as shown in different youtube-guides - and measurements, oil amounts/heights and torque specs completely as stated in the manual. The bushings show no wear at all (and even if they were worn out, I don't think i would make them THIS harsh)
All this makes absolutely no difference at all. They are still way too stiff.
Although I highly doubt it, maybe the previous owner had it revalved? What else could it be?


The only thing that worked for me was to drain 30cc's of oil from the inner cartridge (which I know is the wrong solution)

Just for the experiment, I tried putting in a correctly filled (and bled) inner cartridge into a fork without any oil in the outer chamber - and weirdly, it felt exactly the same. I am really beginning to think something might be wrong.
To me, it feels like a way to high spring rate, but it is the stock one, so not really sure where to go from here.

Thanks to everyone who replied already, I appreciate it!

karlz wrote:

Even if the bushings still have the Teflon coatings on them, but are rough texture and not silky smoothe the forks will bind. One of many many things I have learned in 30yrs servicing suspension.

Correct, the Teflon actually comes off and is suspended in the oil, I change them every 20hrs, also forks don't just go up and down they are side loaded hard.

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5/28/2020 2:13 AM

UPDATE:

Thank you everyone for your replies! I am so happy to be a part of the motocross community where people from the other side of the world are willing to help out idiot strangers like me. This sport is awesome.

I think I might have figured it out - doing this little writeup if anyone else has the same problem in the future. While a lot of you mean people were hating on my poor bushings ( :D ), I tried draining the forks completely and filled them agin - this time making sure I was bleeding the inner cartridge correctly. I took out 30 cc's of oil in the outer chamber. Initially, I thought it made no difference. I stood besides the bike compressing it and it felt as stiff as I'm used to - but now, I rode it a couple of times and even though I didn't replace the seals, I think it had to break in a little. Either way, it made a difference. It is so much better now. Before I would have crazy headshake when trying to go fast over little bumps - now I i just twist the throttle and hold on and it works beautifully. I still think it is a little stiff, but that may be because I compare it to my dads 2013 yz250f which is really soft.

Next time, they'll get new bushings and hopefully that will give me the last 5% of comfort on the bike.

Advice for all you guys trying to rebuild your forks on your own: Bleed your inner cartridges correctly and get out any excess oil so it doesn't bleed out into the outer chamber making the oil level way too high - resulting in way to stiff forks!

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5/28/2020 4:19 AM

You said it has stock springs, 4.6 in there. Stock is .43, if you are running .46 springs your forks will be stiff with your weight and speed

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5/28/2020 5:05 AM

chump6784 wrote:

You said it has stock springs, 4.6 in there. Stock is .43, if you are running .46 springs your forks will be stiff with your weight and speed

I don't know what unit you are reffering to, but in europe we typically use newton meters. My manual states that the stock spring is 4.6 NM in EU-model. I even bought new ones that were definitely 4.6 NM and compared to the stock ones that were in it and they are completely the same.

But thank you for trying to help!

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