H Series with KYB SSS Forks from 16' YZ250F

[ebulic19]

Hello all,

I recently purchased a full front end off of a 2016 Yamaha YZ250F. Included in this was the triple clamps, forks, wheel, and full front brake. I have begun to mock things up and ended up purchasing the steering stem bearings with the assumptions that I will not be pressing in the OEM KDX stem.

Based on my knowledge the bearing dimensions are as follows.

YZ250F
Upper bearing: 28x52x16 mm
Lower bearing: 30x52x16 mm 

KDX 200
Upper bearing: 25x47x15 mm
Lower bearing: 30x55x17 mm

This lead me to purchase the following bearing sizes.

Upper bearing: 28x47x15 mm (off of Amazon from a Chinese retailer)
Lower bearing: 30x55x17 mm (NSK bearing)

Upon looking at the YZ stem in the KDX head tube a little closer, it appears that it is slightly longer than the KDX stem. With that I have read on here that there is mainly one option, being option one below. Has anyone tried options two or three below?

1. Shim the upper bearing race slightly higher to get more crush to adjust steering movement. This appears to be done by either putting a shim on top of the bearing or underneath the outer race, if I am thinking of it correctly.

2. Take a 28 x 1.0 metric die and tap threads a little lower on the aluminum stem to where the steering adjustment nut then puts enough pressure on the upper bearing. Coupled with this I would run a concial washer on top of the top triple clamp, so I do not bottom out the flange nut on the top triple before getting the nut torqued to spec.

3. Press the stem slightly lower in the bottom triple clamps, effectively lowering the overall stem length to where it is closer in total length to the KDX stem.

Any insight is appreciated.

[Chuck78]

Where is the upper bearing steering stem position bottom limit located at in relation to the bottom of the actual bearing installed in the frame as stock, with the updated adapter bearing size? If it is anywhere in the vicinity of the bottom of the bearing give or take 2 mm, I would run it as is, and if you needed additional stack height on top, which from memory should only be a few millimeters, I would add an extra spacer above the bearing and seal on the steering stem, in order to get the lock nut to clamp down properly.

[Chuck78]

The only reason I would shim the upper bearing outer race higher in the frame with a custom shim would be if I were using the Japanese NSK (or All Balls version) 30x47x12 bearing where the KDX frame itself is 15mm tall, which one other's wise results in the bearing being 3mm down in the hole since it's a skinny profile height bearing.

I have a couple of these bearings for my swaps, the 30x47x12 NSK bearings... Pyramid Parts stoped selling the kit that I bought that includes the seal and a 3mm spacer, so that's unfortunate, but the bearing is still available from them. I'll have to look and see as the seals came from the USA and bearing from japan, even though pyramid Parts is from the UK somewhere. So perhaps I can get a part number off of the USA made seals and just get those separately. Cutting a spacer in my lathe there's no problem. Finding the time to work on fun projects is the only problem for me these days!

All Balls sells that kit readily, 30x47x12 with spacer and seal, but for your application, you would still need a custom machine to match up to the 28mm stem, a bearing reducer bushing that is 1 mm wall thickness with a large flange on the top like a washer to sit on top of the bearing and seal and keep the spacer sleep from sliding down on the stem into the frame.

[ebulic19]

Update - I ended up getting the bearings in that I had ordered. The outer races pressed into the KDX stem without issue. I also got enough crush on the upper steering bearing without having to tap more threads onto the steering stem itself. I ended up modifying some of the upper bearing seal off of my KDX to cover the new upper steering bearing. The bottom seal sat on top of the bottom triple without issue. I also included washed underneath the flange nut that tightens the triple clamps down as I was bottoming that nut out. Forks mocked up well but appear to be way too long. Potentially needing to shorten them internally by about 1 to 1.5 inches. I also will need to weld on a steering stop tab as the lower triples miss the stops by being slightly lower than the KLX triples.

So far this appears to be a viable option based on stem length.

[Chuck78]

Perhaps one of these might correct the steering stop position and range? Or fabricating something very similar. Mounted upside down, it would lower the stop location if that's needed .

https://trickeng.com/product/kx125-250- ... p-adapter/

[ebulic19]

Do you have experience with that product? Is that to stop any potential chipping of the aluminum stops via the steel steering tab on the front of the frame?

[Chuck78]

Do you have experience with that product? Is that to stop any potential chipping of the aluminum stops via the steel steering tab on the front of the frame?

I have not purchased this and I likely would just fabricate my own to my exact needs and specifications as I have some basic manual machine shop equipment in my home shop, but this stop is made I believe for those fitting modern KX450 forks onto a KX500 frame. The KX500 frame will have very similar steering stops as the KDX and KLX. KLX300 triple clamps on a KDX 220 / 200H come up just a slight bit short, but are almost perfect. The fork does hit the gas tank.

So I would imagine this would be pretty close or maybe too much and need ground down. I'm not sure if you could find out the dimensions of this and compared to what your bike needs, but this style of stop fixes a lot of problems.