KDX250 springs finally

Tom68 · Jul 12, 2010

Ordered 0.44 springs today for my 250sr, the seals started to leak after three years of running between 15 and 25psi with standard 0.29 springs :yikes: , always having positive pressure in the legs probably helped the seals resist packing with dirt.

If the sr comp' valves are the same as the U.S model I'll remove some high speed shims.

Just wondering if I should use a heavier oil for more rebound, currently using 5W and feel it could use more rebound damping.

Tom68 · Jul 14, 2010

Springs arrived, were supposed to be 38.6mm O.D but are 39.3mm and don't fit in the legs.

Tom68 · Jul 15, 2010

Checked the base valve and the high speed compression stack only has two shims, the ports are very small though, not keen to disassemble the cartridge, don't want to damage it, trying to find out more about the piston rod bush, it's either a floating type or mines shot.
Still can't workout how the US model gets a longer spring, everything in mine appears the same as in the U.S manual I'm using but my spring fitted length is 455mm, bottomed length is 165mm. I assume the other 10mm of travel is counted as the rebound spring.
I can understand why you'd want a 505mm spring if it was 0.34 or 0.35kg/mm but for a 0.44 460-465mm will be the right length for these.

glad2ride · Jul 15, 2010

On the USA models, the bushing is a solid piece. Call Terry Hay as Race Tech has the bushings. The cartridge must be disassembled. I have their cartridge clamps and the OEM tool to disassemble the cartridge. I would hate to even guess how someone would try it without the proper tools.

The distance taken up by the spring in the USA forks is 490mm. The USA model is a KDX250, not a KDX250SR. We never got the SR model. Ours is a dirt only version.

Tom68 · Jul 15, 2010

glad2ride said:
On the USA models, the bushing is a solid piece. Call Terry Hay as Race Tech has the bushings. The cartridge must be disassembled. I have their cartridge clamps and the OEM tool to disassemble the cartridge. I would hate to even guess how someone would try it without the proper tools.

The distance taken up by the spring in the USA forks is 490mm. The USA model is a KDX250, not a KDX250SR. We never got the SR model. Ours is a dirt only version.

Thanks, got them apart, warmed up to release loctite and they weren't mechanically very tight, just a teflon bush in these to, loose on shaft and in holder.

glad2ride · Jul 16, 2010

Good job. Heat does in deed help out on that.

On the USA KDX250 forks, one would need to get the rebound valving assembly off to get the bushing changed. I ended up filing a hex shape on the end of my assembly to better get a grip on it, compared to the stock two flat sides configuration.

I am glad to hear you are trying to get some stiffer springs in there, instead of the air method you had been using. Once you get it going, I think you will really like it.

Tom68 · Jul 16, 2010

glad2ride said:
Good job. Heat does in deed help out on that.

On the USA KDX250 forks, one would need to get the rebound valving assembly off to get the bushing changed. I ended up filing a hex shape on the end of my assembly to better get a grip on it, compared to the stock two flat sides configuration.

I am glad to hear you are trying to get some stiffer springs in there, instead of the air method you had been using. Once you get it going, I think you will really like it.

Rebound valve has to come off to.

Air was to get me some bottoming resistance with std springs but am looking forward to a more linear spring rate in the front.

Tom68 · Jul 22, 2010

Ended up with 486 long 38.3 O.D .46 springs, free length is too long but I'll fix that, they just make the bottomed clearance at 160mm, 5mm to spare.

Now I need cartridge bushes, 14mm O.D 10mm I.D 9mm high. Prefer genuine KYB for correct tolerances, local racetech agent doesn't have them not even in racetech branded.Bit of a one off size nothing similar in KX's from '94 to present KLX may be the same, can't find listing.

EDIT. going to machine down some 15mm aftermarket bushes.

glad2ride · Jul 24, 2010

Call Terry Hay, at whatever his shop is. He is in AUS. If you search on dirt bike world, you will find him.

1988 KX125 / KX250 and KX500 have a 10mm diameter cartridge rod. 1990 and newer are all larger.

I think KLX300 (at least in the USA) are the same.

Good luck on getting them down to size.

Race Tech used to have some KX ones that were a blue plastic or other material.

Tom68 · Jul 24, 2010

glad2ride said:
Call Terry Hay, at whatever his shop is. He is in AUS. If you search on dirt bike world, you will find him.

1988 KX125 / KX250 and KX500 have a 10mm diameter cartridge rod. 1990 and newer are all larger.

I think KLX300 (at least in the USA) are the same.

Good luck on getting them down to size.

Race Tech used to have some KX ones that were a blue plastic or other material.

Looks like the sr factor kicks in again, got 15mm bushes off Terry, looked up KYB catalogue for bushes and looks like the sr is an unlisted orphan.

Matt90GT · Aug 2, 2010

all this time on these forks IMHO is a waste of time. They are just about the same as a XR50 fork - worthless.

Get a set of KX250 forks off Ebay and swap them. Better valving, and rebound adjustment and people know the parts for them.

Tom68 · Aug 2, 2010

Matt90GT said:
all this time on these forks IMHO is a waste of time. They are just about the same as a XR50 fork - worthless.

Get a set of KX250 forks off Ebay and swap them. Better valving, and rebound adjustment and people know the parts for them.

Good advice.

I'd also be better off getting a KTM200 and leaving the KDX at the farm, but I'm a bush basher who's forks needed seals so I'm giving them a freshen up whilst they're apart, rebound adjusters would be great but I haven't changed the bump adjusters.

Funny you should mention XR50 forks, my other bike is a XR500 and I don't mind its 37mm damper rod forks, takes 20 psi to reduce the bottoming though.

EDIT. She's back on the ground and feels good, hope to ride this weekend.

Matt90GT · Aug 4, 2010

FYI -XR50 forks are bushings, grease and springs. No oil

Tom68 · Aug 4, 2010

Matt90GT said:
FYI -XR50 forks are bushings, grease and springs. No oil

Just one step down from a damper rod.

Matt90GT · Aug 5, 2010

or a double pogo stick! LOL

Tom68 · Aug 8, 2010

Finally got a ride.

Was 0.29 springs no preload with 15-20psi 130mm oil level.

Is 0.46 springs 10mm preload, 0psi, 100mm oil level, new cartridge bushings increasing damping across the range.

Front wheel initially strikes the ground harder on flat landings, but it doesn't matter.

Much better on hard full bottom out landings, obviously starts retarding the downward motion better high in the stroke.

Heaps better down steep hills, maybe rides a tad higher but still has compliance.

Up hills not sure but I got fired off the pegs over a root that I wasn't expecting to get any trouble from.
But the back wheel most likely hit a step at the same time.

Seems more sure footed on the faster single trail.

Much easier to bounce the front up in 4th.

Yeh I know it's an old ****ter and not worth the effort but somebody may get something out of it.
__________________
KDX at the Broadmeadows table top.
http://i698.photobucket.com/albums/vv347/Tom65/BMX6.jpg

glad2ride · Aug 10, 2010

Hey, all right! Good job and report.

KDX250 springs finally

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