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.