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2015 YZ250 inner cartridge seals/Bushings?

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I will be servicing the Forks on my 2-stroke pretty soon. I have about 50hrs on the bike now. I have changed the metal slide and piston bushings, oil seal and wipers a couple times now.

However I have never changed the inner cartridge rod Bushing and seal before.

Is these items hard to do? I have changed the seal head bushing in the shock though, so I know how to press the bushing in an out to replace it.

Just not sure if the forks inner cartridge rod bushing is done the same way or close to the way as you would do it on the shock.

I am sure by now this inner cartridge rod bushing that is in the forks is ready to be replaced by now. Been 2 yrs/50 hrs.

Here is a image of the bushing I think is the one I need, along with the seals. These images are from SDI direct.

f14.jpgf15_7.jpg

Here is what it says about the seals.

12.5mm Cartridge Seal Backup 06-09 YZ (all), 07-09 KX450F, 09 CRF450R ea..ID-12.8mm OD-17mm TH-1.8mm.

Is this the seal I need that is located at the bottom portion of the inner cartridge tube? In other words......like when you are taking the inner cartridge apart and you unscrew the jam nut off of the end of the rod.

Then when you push the rod up through the Top portion of the cartridge to take this rod out.

Is this seal located at the bottom portion of the cartridge?

And exactly where is the Fork Bushing located at?

Sorry for all the ?'s. Just trying to learn and once I have thus part figured out then I will be able to rebuild the whole Fork by myself. Then will just need to learn valving.

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50 hrs is not much if the oil is kept fresh.  Unless your leaking, which will be obvious during cartridge bleeding,  just clean, reassemble and ride.   Drill your free pistons also.  I have probably close to 200 hrs on stock cartridge rod bushings/seals. 

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Keep them as spares if you ever need them.  You may or may not ever wear out the ones in there now. 

How many times have you replaced the fork seals and bushings at 50 hours?  I'm all about preventative maintenance but that sounds like a lot more $75 rebuild kits and expensive oil than you need to be buying.  I do them whenever they start leaking.  I do change the oil pretty frequently which prevents the accumulation of metallic debris and any dust or grit that gets past the seals.  I think the last set of 48mm KYB's I rebuilt with genuine KYB parts was going on two years on that set of seals and bushings.  Had to be close to 100 hours on them, albeit almost entirely in dry and dusty conditions with no mud drying on the tubes and chewing up the seals.

Unless you're running them in some serious mud most of the time I wouldn't think of running them for less than 50 hours, with a few oil changes during that interval. 

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Outer seals and bushings should easily be getting over 100 hours with moderate use and even longer for cartridge seals and bushings.

If you are going through seals and bushings this often, something is off.

What kind of oil are you using?

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50 hrs is not much if the oil is kept fresh.  Unless your leaking, which will be obvious during cartridge bleeding,  just clean, reassemble and ride.   Drill your free pistons also.  I have probably close to 200 hrs on stock cartridge rod bushings/seals. 


Wow! I thought those rod bushings should be replaced seasonal or at least every other year.
I keep fluid changed about every 15hrs. I like about 3 more hours til I have reached 15 hrs.

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Keep them as spares if you ever need them.  You may or may not ever wear out the ones in there now. 
How many times have you replaced the fork seals and bushings at 50 hours?  I'm all about preventative maintenance but that sounds like a lot more $75 rebuild kits and expensive oil than you need to be buying.  I do them whenever they start leaking.  I do change the oil pretty frequently which prevents the accumulation of metallic debris and any dust or grit that gets past the seals.  I think the last set of 48mm KYB's I rebuilt with genuine KYB parts was going on two years on that set of seals and bushings.  Had to be close to 100 hours on them, albeit almost entirely in dry and dusty conditions with no mud drying on the tubes and chewing up the seals.
Unless you're running them in some serious mud most of the time I wouldn't think of running them for less than 50 hours, with a few oil changes during that interval. 


I have replaced my Fork piston Bushing and metal slide, wipers and seal twice all ready. The First set I replace was at 30ish hours.
Second set was because forks felt funny to me riding at the track one day. I had the clickers turned all most all the way open.
Took the right fork tube apart to find that the top portion of the inner cartridge had came unscrewed. Reason why I replaced the bushing,slide and seal,wipers then was because when I was separating the outer tubes I messed up the Teflon on the outside of one piston bushing.
Now I take some map gas and heat the outer tube up around about where the seal is located so that it makes separating the tubes easy.

Seems like to me my parts look worn at the end of each racing season. I usually have around 18 races in 2 classes plus practices when there isn't any races.

So The Forks and shock get a good bit of beating.

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Outer seals and bushings should easily be getting over 100 hours with moderate use and even longer for cartridge seals and bushings.
If you are going through seals and bushings this often, something is off.
What kind of oil are you using?

I ain't saying I am going through seals and bushing. Matter of fact......the times I change bushing,slide,seals,wipers..... The seals have never leaked.
However though...... I race MX only and Race in the Vet Expert A class. The Forks and Shock go through a beating. When I change the fluid out at around 15hrs, the bushing and slide still have copper around the inside and out side but do show some wear.
This time when I change fluid in the Forks the bushing and slide and seals,wipers will have 41 hrs on them.
I will just change fluid this time and wait till the next 15 hrs before I check em again. I will post pics on here when I change my fluid so you can see how much the bushing and slide has worn.

I use Yamaha S1 Suspension Fluid in Forks and Shock.

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Keep them as spares if you ever need them.  You may or may not ever wear out the ones in there now. 
How many times have you replaced the fork seals and bushings at 50 hours?  I'm all about preventative maintenance but that sounds like a lot more $75 rebuild kits and expensive oil than you need to be buying.  I do them whenever they start leaking.  I do change the oil pretty frequently which prevents the accumulation of metallic debris and any dust or grit that gets past the seals.  I think the last set of 48mm KYB's I rebuilt with genuine KYB parts was going on two years on that set of seals and bushings.  Had to be close to 100 hours on them, albeit almost entirely in dry and dusty conditions with no mud drying on the tubes and chewing up the seals.
Unless you're running them in some serious mud most of the time I wouldn't think of running them for less than 50 hours, with a few oil changes during that interval. 


How do you set the preload on the Forks? Do you do it by buying those preload rings and put them in?
If so......I was thinking about buying 4mm's and putting 4mm's of preload on each Fork.
Reason why.....is because I think my Forks are a tad on the soft side and they ride a little low.
I have had the Forks valved and sprung for my weight at that time which was 175 lb. Now I am at 165lbs but still that isn't much difference.

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Here is what I was thinking.
Getting the 5mm spacers.
Just got to figure out how to get them on.
Any ideas?
f29-2_2.jpg

SDI Elite Fork Preload Spacers - 5mm
- The easiest way to adjust preload on Twin Chamber Forks
- For forks with 24mm Cartridge Rods
- Available in Three Different Sizes
- Sold in Pairs
- Made in the U.S.A.

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What is your sag with current setup?

Right now my race sag is 102mm with a free sag of 30mm

I am wanting the bike to ride a little higher up in the stroke like on my 2016 YZ450. It has stock 5.0kg springs in forks and a 5.6kg rear spring.

However though .......my 2016 YZ450 valving is stock. It's stiff but I like it because it rides high up in the stroke.

My clickers on it are opened up though.

All lost all the way on Forks Comp and Rebound. Shock's comp is also at 18 clicks out.

I just need my 250 a little bit more stiffer/Plusher. It's not too bad now but would like it to bit a bit more stiffer in the upper part of stroke on forks and shock.

Not the valving harder/stiffer but for it to ride a little higher in the stroke if that makes since.

I thought if I put a 5mm preload spacer on the forks that would help achieve what I am wanting. Maybe get a next stiffer rate spring on rear also. I may need a stiffer rate springs in forks also.

What do you think? I belive my valving is good. Just need to do something to make it a tad more Plusher in the upper part of the stroke on forks and shock.

Forks I believe have the next rate stiffer in springs in it than stock like 46kg. May benefit with 48kg.

Rear I believe is a 5.1kg may benefit with a 5.6kg like on my 450.

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Need to know your fork sag.  Just like race sag in the rear, measure when fully extended on a stand and measure them with you on the bike and the front end settled.

You're probably already where you want to be in terms of sag and preload.  Would likely cause other problems trying to fix a valving trait with springs.

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I will do that before I go riding after while. I will do it with all my gear on. I will first measure from bottom of Fork lug (like the square part where the axle pinch bolts are) to where the chrome piston goes inside the outer tube.

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You can just have someone mark the tube with a sharpie with you on the bike and then measure the gap with the fork fully extended.  Or put a zip tie on the leg.  Doesn't have to be too scientific.  Just measure the gap.

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You can just have someone mark the tube with a sharpie with you on the bike and then measure the gap with the fork fully extended.  Or put a zip tie on the leg.  Doesn't have to be too scientific.  Just measure the gap.

My Fork sag measurement was 43.66mm's which is 1.7188976 inch's

Is this too much? I know on my 2016 YZ450, I can just barely get the fork to move. It goes down about 2mm.....lol
Its pretty stiff.

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That's just about right.  I'm at 45mm and I'm running more preload than is recommended on stiffer springs than are recommended.  I wouldn't run any less if I were you. 

You could try stiffer springs with the same or even less preload.  That would keep the sag right and make them stiffer in the mid stroke.  That might work if you don't want to change valving.

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That's just about right.  I'm at 45mm and I'm running more preload than is recommended on stiffer springs than are recommended.  I wouldn't run any less if I were you. 
You could try stiffer springs with the same or even less preload.  That would keep the sag right and make them stiffer in the mid stroke.  That might work if you don't want to change valving.


Do you mean same Preload or less that is on the rear Shock spring? Like leave it at 102mm or maybe down to 98mm?

I don't really know how to change preload on Forks other than using those preload spacers that you buy. I have never used them and don't have any in the forks now.

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I am referring specifically to the forks. 

Adding preload requires spacers or longer springs.  Removing preload requires internal mods to the fork spring seats.  You're already on the low end of the fork sag realm so you're limited in terms of what you can do.  Going to stiffer springs will reduce your sag by a certain amount and you're already running very little.  You can always try it and see if you like it.  That's what really matters.

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I am referring specifically to the forks. 
Adding preload requires spacers or longer springs.  Removing preload requires internal mods to the fork spring seats.  You're already on the low end of the fork sag realm so you're limited in terms of what you can do.  Going to stiffer springs will reduce your sag by a certain amount and you're already running very little.  You can always try it and see if you like it.  That's what really matters.


Well....if I did try some stiffer springs, would you go up a rate stiffer on the rear shock also?
Sorry for all the ?'s. But just talking with you about this has helped me really understand more about preload, on how to get more preload and take preload off. Also on how to measure fork sag and knowing how much fork sag one should have.
You have really helped me learn a lot more.
I will try and find me some good used springs to try out sometime. What rate would you recommend on springs?

I weigh 168lbs and the springs in my bike now are probably a size stiffer than what stock was. I have my stock springs that were in the bike in my shop. Don't know exactly what rate the tuner put in. Just guessing......he probably went one rate stiffer but not sure.
I believe 44kg was stock and he probably put in 46kg ones. So I could go to 48Kg.

Is there a method you can use to test the rates of the springs when you have them out? Same for rear spring?
Probably have to have some kind of scale.

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You don't have to change the rear rate.  Won't affect rear sag regardless of what you're running in the forks.

There are spring rate testers but its not usually done.  Aftermarket springs should be marked.  They can vary but I wouldn't worry about it.

If you like the way your other bike feels run the same springs you have in that one.  If you go stiffer it may reduce the sag but if you like it run it.

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