KX Fork Conversion / Required Knurling?

[Bigdavelittle]

I have just had a 2006 KDX stem pressed into a 2002 KX lower clamp, no knurling required. Pressed in nicely.
The KDX stem was very tight to remove from the KDX lower clamp, the KX stem came out way easyer.

[SACTO_STEVE]

I JUST DID A KX SWAP THE FRONTEND WAS FROM A '96 KX250 ALL THAT WAS REQUIERED WAS TO SWAP STEMS AND TO MACHINE TWO SPACERS (ONE FOR THE PRELOAD ADJUSTER AND ONE FOR THE TOP STEERING NUT) DO TO THE LENGTH OF THE KDX STEM IN THE KX TREES

[ITracerMike]

I just installed a 2001 KDX stem into 2004 KX250 clamps with no press required. We use liquid nitrogen for chilling large shafts at my work so while a tech was chilling a shaft this morning I placed my stem into the container of liquid nitrogen long enough for me to warm the bottom clamp to approx. 180f . I was able to slip the stem into the lower clamp with virtually no resistance and held it long enough for the clamp to cool to an interference fit. For those without access to a press you may be able to get the same results by freezing the steering stem ( leave in deep freezer overnight) and heating the lower clamp just as I did . note: all parts were measured beforehand to confirm an interference fit upon assembly.

[GATOROC]

Thought I'd add my experience on here as well. I picked up a complete 1997 KX250 front end, and after pressing out the KDX/KX stems and putting the KDX stem in the KX lower clamp, it had very little resistance and could be pressed in buy hand. I finally found a shop to do the required knurling and then it was able to be pressed in properly.

[rampeyboy]

1999 KDX200. Used 1994 KX250 front. Did not need to knurl bottom clamp. Did require press to remove and install stem. Used .020 aluminum around top of stem for "bushing" where top clamp fits. Worked perfect. My bars are 7/8 so had to swap the bar mount from KDX to KX top clamp. Only thing left now is to secure the brake line to the fork shield and put KX rim on front and ride!

[Chuck78]

As an alternative to knurling + having a custom spacer machined for the upper triple onto the stem, you could look into a custom steering stem from Emig Racing:

http://www.emigracing.com/steering-stems.html

I also saw that KX Guru sells stems to fit later forks onto a KX500 (KX500 uses same bearing sizes as KDX frame and stem), since the earlier KX forks use a different stem press in diameter at the lower triple (96 and older). I think it was 2006+ KX250F Showa Twin Chamber forks that the stems are intended for. Those are REALLY NICE FORKS...


I also was wondering if anyone had ever tried just using the KX stem (IF it's the correct height for the KDX frame) and instead of doing a stem swap, keep the nice aluminum stem and machine an upper bearing spacer + top hat shaped stem (bearing ID) spacer instead? This would have been the obvious first choice for me if I hadn't heard of the prevalence of knurling the stems...

The KDX upper bearing is 25mm i.d. x 47mm o.d. x 15mm tall. So the KDX frame takes a 47mm o.d. bearing that's 15mm tall.
The KX stems upper bearings are 28mm i.d,
So we'd ideally use a 28x47x15 bearing, right? Well, they are nonexistent. Not a standard size.

BUT...

a 30 x 47 x 12 bearing is in fact available... All Balls part # is 99-3540-5.
You can also get a Japanese NTN bearing, I've purchased two + their appropriate upper seals from Pyramid Parts overseas in the U.K.

a 30 x 47 x 12 bearing could be fit onto a stem with a 28mm upper bearing diameter, using an upside-down top hat shaped stem spacer 15mm tall and 1mm wall thickness where it sleeves inside the bearing over the stem, to make this a proper fit, and then either have the wider brimmed portion above that be 3mm tall to come up to the top of the frame, or perhaps machine a 47mm o.d. spacer 2mm thick to press into the frame UNDER the upper bearing, and have the top hat flange above be only 1mm tall to keep the spacer from dropping down through the bore of the bearing...

I am baffled as to why no one has chosen this route with this common bearing size in the past, as you're paying the machinist to do about the same amount of labor or perhaps even less since pressing stems out can often be incredibly painstaking, with 20,000lbs pressure and heat from a torch required...

I bought a set of 97-04 KX500 forks at a great expense (as they use a stem nearly identical to the KDX with the KDX bearing sizes = direct swap) because I hadn't figured this out prior, but now I'm looking at the KX125 triples with a slightly different offset and the aluminum stem, and thinking that'd be nice to save weight with an aluminum stem and also have geometry change options. Seems a no brainer to me, but the deal breaker would be if the bearing surfaces on the KX stem were not within the height range needed for the KDX frame.

UPDATE - I'm doing this exact configuration on a 2019+ KX450 triple clamp with a 30x47x12 NTN upper bearing and adapter to 28mm stem, although I think these 2019+ KX450 / 2021+ KX450X / 2025+ KX250X / 2026+ KDX300R forks may possibly clamp into the same era of CRF450 triple clamps as they are both the same forks although there might be variations on the clamping diameters. The CRF450 uses 22mm offset vs 23 on the KX, & 30mm upper bearing size vs 28mm on the KX, and maybe a more appropriate length steering stem, the 450 steering stem is about 6 mm taller than needed but this is easily workable as the steering stem bearing surface extends down to exactly where it needs to go to in regards to the KDX frame. That actually raises the triples and allows you to slide the forks up higher on the bike, lowering the effect of the taller forks. No bearing adapter bushing required would be nice though if the CRF triples work, although they may be nearly the exact same triple clanps.

I've also swapped an aluminum Suzuki VStrom DL1000 steering stem into 98 RM125 triple clamps (almost the same steering stem but in a taller correct bearing spacing height perfect for the KDX other than the stem protrudes above the thinner RM triple clamp higher. Using the same 30x47x12 bearing size, 30mm stem o.d. upper and lower.

[Chuck78]

If anyone could perhaps take a photo of a KX stem with a tape measure next to it where the lower bearing would have seated, or hold it directly next to a KDX stem, that'd be awesome to confirm or debunk this method. Thanks!

[SS109]

IMO pressing stems is super easy and I have done it on my Harbor Freight 20ton press and have never needed heat. The knurling is the hardest part but you can do it yourself at home, by hand, with the proper tool. Also, plenty of people have done a fork swap without using RB's top adapter but it does make the install look nice and works better than the DIY solutions I've seen.

On to your question, IMO, the setup you're suggesting would introduce a weak point. The KX stem is longer than the KDX stem and where the bearing seats on it would be higher than the stock KDX frame can accommodate. By introducing an adapter to raise the bearing out of the frame to the proper height, the bearing itself (and the loads placed on it) would be outside of the frame and creating leverage on the adapter. The adapter would have to be made from a nice alloy steel that can be press fit in to the where the KDX top bearing race would normally reside and then be strong enough to contain the stresses of the leverage placed on it by side loading. This would still more than likely lead to binding to some degree and, at worst, breakage/bearing failure due to the side loading. However, this is just my educated guess and maybe I'm overthinking it. If I'm misunderstanding what your saying please let me know. I'm a visual based creature and sometimes miss what someone is trying to explain.

[KDXGarage]

I am thinking a 1 mm thick sleeve / shim between the stem and frame might do it. Just stack a 3 mm washer on top to take up the missing height. You better get it to not be sloppy though. :-)

2003+ KX stems are 6 mm taller. I don't know when the bearing area starts / ends in case it does not line up.

Maybe you have used your modern computer to look up something that was not so readily available back in 2004 when the fork conversion subforum got started. :-)

[Chuck78]

Well this could work if what SS109 is referring to is the 2003+ KX stems being longer. As long as the 1992-2002 KX stems are close enough to the KDX bearing locations, the upper bearing spacer sleeve idea might actually work! I'm curious particularly for a 1996-1997 KX125 or 250 triple clamp as it will work on my 1997-2004 KX500 forks. Although I have the KX500 triples which have basically a KDX steel steering stem, so they are a direct bolt-on. Some people have pointed out that the KX125/250 have a different offset than the 500, and 500 owners preffered the 125/250 offset better. KX owners is the key here. The 97+ KX500 was basically just a novelty BIG big bore play bike at that point, as there were no longer open classes for these suicidally fast machines to run in at sanctioned races.
Also according to KX Guru Racing, 1997+ KX500 stems are a larger press fit diameter than 1996 & earlier...
KX Guru Racing also sell billet steering stems for the older 500's whose steering stems don't as easily swap into the newer choices of upgrade forks without the knurling etc.
Emig Racing also makes custom steering stems per customer spec.

Personally the knurling to make a slightly sloppy fit into a tight fit somewhat bothers me, but with permanent cylindrical bonding spec loctite or other brand retaining compound, I doubt anyone would have trouble with a knurled stem.


Regarding RM125 Showa Twin Chamber 49mm & 47mm forks 1996-2008, I revisited the V-Strom DL1000 triple clamps which would work for some of my vintage street bike swaps. They have the same type of aluminum steering stem as the '96+ RM125/250, DRZ400, & probably '06+ RM-Z - with 30 mm ID bearings as what the RM Showa forks do, as well as GSXR & Hayabusa models 1990's & 2000's...
The VStrom DL1000 steering stem is the exact bearing spacing height for the KDX frame, and will swap perfectly after milling the raised pad off the RM triples' loser bearing seat area to make it a normal thickness triple clamp... I just got a VStrom DL1000 triple in the mail today for $12.98 + shipping as a steering stem donor. Coincidentally the shorter RM or GSXR steering stems that I have, swapped into this V-Strom triple clamp, will also solve my street bike fork swap problems!
One member bored out the lower triple from underneath so that the stem sat up higher, as well as milling off that raised step. I don't like the idea of less and less press fit area, I'm okay with milling the top flat, but recessing it from the bottom as well is too much. These v-strom stems are commonplace for cheap. Non-ABS models, it has to have the aluminum steering stem, ABS models have a steel steering stem for some reason. Newer and different forks.
RM250 used Showa suspension 1996-2000, but lapsed a few years & ran KYB instead. I'm not sure if the triple clamps were the same, But it seems to be a Suzuki steering stem theme to use the aluminum 30mm upper and lower bearing stem from the mid 1990's & on, as well as Honda CR125+ / CRF250+

[KDXGarage]

I remember someone mentioning your portion of the bearing area being too thick for a few mm when putting a KDX stem into some KX lower clamp. The thickness of the clamps is different.

A lot of people have ran with knurled stems. This website is approaching 18 years of fork talk. :-)

[Chuck78]

I remember someone mentioning your portion of the bearing area being too thick for a few mm when putting a KDX stem into some KX lower clamp. The thickness of the clamps is different.

A lot of people have ran with knurled stems. This website is approaching 18 years of fork talk. :-)

Yes I believe that was the original reason for having it machined down, but I realized it would solve a problem when using the original Suzuki aluminum stem still as well.

When the motocross bike steering stems are a much nicer aluminum stem, I don't see the point of putting in a substantially heavier steel stem that has to be knurled in order to obtain a fairly tight fit, when you have the option to pursue other methods and end up with a better result and a lighter weight steering stem without any knurling needed.

[KDXGarage]

The KDX250 has an aluminum stem. I think it is the "smaller" OD. The later KX ones and last KDX one is a touch larger.

I took a 1996 stem out. It was huge compared to all the other ones I separated. This was 16 years ago, so I can not remember all the specifics. :-)

[Chopperpilot]

As an alternative to knurling + having a custom spacer machined for the upper triple onto the stem, you could look into a custom steering stem from Emig Racing:

http://www.emigracing.com/steering-stems.html

I also saw that KX Guru sells stems to fit later forks onto a KX500 (KX500 uses same bearing sizes as KDX frame and stem), since the earlier KX forks use a different stem press in diameter at the lower triple (96 and older). I think it was 2006+ KX250F Showa Twin Chamber forks that the stems are intended for. Those are REALLY NICE FORKS...


I also was wondering if anyone had ever tried just using the KX stem (IF it's the correct height for the KDX frame) and instead of doing a stem swap, keep the nice aluminum stem and machine an upper bearing spacer + top hat shaped stem (bearing ID) spacer instead? This would have been the obvious first choice for me if I hadn't heard of the prevalence of knurling the stems...

The KDX upper bearing is 25mm i.d. x 47mm o.d. x 15mm tall. So the KDX frame takes a 47mm o.d. bearing that's 15mm tall.
The KX stems upper bearings are 28mm i.d,
So we'd ideally use a 28x47x15 bearing, right? Well, they are nonexistent. Not a standard size.

BUT...

a 30 x 47 x 12 bearing is in fact available... All Balls part # is 99-3540-5.

a 30 x 47 x 12 bearing could be fit onto a stem with a 28mm upper bearing diameter, using an upside-down top hat shaped stem spacer 15mm tall and 1mm wall thickness where it sleeves inside the bearing over the stem, to make this a proper fit, and then either have the wider brimmed portion above that be 3mm tall to come up to the top of the frame, or perhaps machine a 47mm o.d. spacer 2mm thick to press into the frame UNDER the upper bearing, and have the top hat flange above be only 1mm tall to keep the spacer from dropping down through the bore of the bearing...

I am baffled as to why no one has chosen this route with this common bearing size in the past, as you're paying the machinist to do about the same amount of labor or perhaps even less since pressing stems out can often be incredibly painstaking, with 20,000lbs pressure and heat from a torch required...

I bought a set of 97-04 KX500 forks at a great expense (as they use a stem nearly identical to the KDX with the KDX bearing sizes = direct swap) because I hadn't figured this out prior, but now I'm looking at the KX125 triples with a slightly different offset and the aluminum stem, and thinking that'd be nice to save weight with an aluminum stem and also have geometry change options. Seems a no brainer to me, but the deal breaker would be if the bearing surfaces on the KX stem were not within the height range needed for the KDX frame.

I ordered this bearing from amazon..... while there I typed in 28mm x 47mm bearing, and guess what? there's one of them too! I have it on order for fitting a 2003 YZ250 front end to a kdx. I'll let you guys know if it works. The bearing is a 28 x 47 x 12mm and should work wonderfully! The factory KDX bottom steering bearing should work as the YZ stem is 30mm at the bottom like the KDX.

[TheScrambler]

I ordered this bearing from amazon..... while there I typed in 28mm x 47mm bearing, and guess what? there's one of them too! I have it on order for fitting a 2003 YZ250 front end to a kdx. I'll let you guys know if it works. The bearing is a 28 x 47 x 12mm and should work wonderfully! The factory KDX bottom steering bearing should work as the YZ stem is 30mm at the bottom like the KDX.

Did that bearing work out?

[Chopperpilot]

The bearing of course is the 'right' size. Did mounting the front end work? Unknown so far, I wasn't going to take apart a running bike during our short riding season. Well at +5f and a foot of heavy snow on the ground I'm in 'winter bike restoration mode'. Unfortunately the storm knocked down trees and I'm still without power a week later (maybe today!) So after I clean up all the mess and organize my garage, I'll start seeing about fitting the front end to the KDX

[Chuck78]

Well in light of Yamaha YZ250 2-stroke steering s/stems being appropriate lengths for the KDX frame, as well as some or all of the Honda CRF steering stems, I've found 2019+ KX450 (& likely 250F) steering stems are a workable length for our bikes, 7-9/16" roughly from lower bearing bottom seat to upper bearing top seat on the stem at the edge of the threads and bearing surface thanks to eBay seller Applegate MX, who has 16 pairs of these 2019+ KX 49mm Showa forks from race team bike take-offs/ part-outs.

The KYB KX250X & especially the 49mm Kashima-coated Showa KX450X off-road model forks get pretty great reviews for trail riding & from suspension tuners, & even the 2019-2023 MX versions were soft enough for woods riding compliance (not '24+ MX), and the X model valving is softer by using one or two less shims and slightly thinner shims but almost the same valve stack configuration aside from shim thickness and mid valve float.

This KX stems use the same lower bearing our KDX uses (30x55x17), but upper bearings differ slightly:
KDX220/200 25x47x15
KX450 2019+ 28x52x16
conversion = 28x47x12 or 28x47x15

All Balls does not have a 28mm ID 47mm OD bearing, but you can find them on Amazon and all over the internet, although this is not an industry standard size and largely seems to be generic Chinese sizes.
AllBalls DOES in fact have 30mm I D. x 47mm O.D. x 12mm tall bearings... While the generics might be just fine, and I might even order one and try it out riding locally, I just ordered some 1" I.D. x 1.5" O.D. 6061 T6 aluminum tube stock, Brinell hardness 95 (Rockwell hardness 60), in order to machine a 1 mm wall thickness bushing 30mm O.D. and 28 mm I.D., 15mm tall, with the top portion being left 1.5"/38.1mm as the reverse top hat type configuration I was referring to previously.
This would also allow me to use the same bearing races for either fork that I have, the 1998 RM 125 Showa 49mm Twin Chamber forks or the 2023 KX450X Showa Twin Chamber 49mm inverted... Maybe the same fork seals as well!

SS109 - I described this a while back in posts above, and you thought that I was trying to make an adapter to raise the bearing up out of the frame and sit outboarded in order to use a longer stem. That is not what I was trying to convey, and I would not use a steering stem that was too long for the job.

This would simply be using a reputable quality bearing of too large of inside diameter and 3mm shorter thickness, and making an adapter to get it down to the 28 mm inside diameter of the KX steering stem, and making up the difference with a 3 mm flange, like an upside down top hat, at the top, so that the spacer does not fall through the bearing, and so that the spacer makes up the height of the bearing back to the full 15 mm thickness to sit level with where the stock KDX upper bearing height would be.

In another paycheck or two after I pay for my broken wrist and a massive amount of parts for the wife's bike, I will probably go ahead and buy some OEM Kawasaki triple clamps for the 2019-2025 KX450/450X, and proceed with this fitment.
The 450 fork springs are all SIGNIFICANTLY stiffer than what a 155 lbs woods rider like myself would require for a lighter weight KDX, but Race Tech makes down as low as 0.38kg/mm, & Diverse Spring makes their lightweight silicon-chrome steel springs in .40kg/mm. I believe both of those rates would work well for me - the .40kg with some slightly lighter ICS compensator springs perhaps, and virtually no preload on the spring if I can manage to adjust it that way in these modern forks.

The forks come at quite a premium price though, but I'm tired of buying eBay forks that the sellers swear are in excellent condition with perfect chrome, only to have them arrive and find impact damage or rust pitting or gouges in the chrome tubes. Buying forks that were used one year by expert and pro racers will ensure that they were in good service and frequently rebuilt, taking care of etc and not a 10 or 25-year-old fork with bad chrome that the seller does not inspect properly... Most of the forks on eBay are takeoffs from MX & GNCC race team bikes.

I'm absolutely in love with my right side up 49 mm Showa '98 RM125 Twin Chamber forks, but they're only 1/2lbs lighter than stock KDX boat anchor forks, so I thought I would try out these pricey modern forks on my other 220 to see how much of a difference in weight vs feel/handling there could be.

[Chopperpilot]

I'm curious why you'd do a sleeve on a 30mm ID bearing over running a 28mm ID bearing? I mean it's not like the All Balls bearings are super premium bearings or anything. In a steering head, they aren't running 20,000 rpm or anything. I'd think that by creating a slip fit sleeve, on what was a slip fit bearing anyway, you just introduced more play and slop into it. Just to run a different chinese bearing?

[Chuck78]

I'm curious why you'd do a sleeve on a 30mm ID bearing over running a 28mm ID bearing? I mean it's not like the All Balls bearings are super premium bearings or anything. In a steering head, they aren't running 20,000 rpm or anything. I'd think that by creating a slip fit sleeve, on what was a slip fit bearing anyway, you just introduced more play and slop into it. Just to run a different chinese bearing?

I have a Koyo(?) Edit - NTN Japanese bearing from Pyramid Parts in the 30x47x12 size already, and this Suzuki RM fork swap that I have on my other bike uses the same size bearing without a bushing sleeve adapter reducer, so I will be able to use the same bearing race and swap forks between one bike or the other if I wanted to.
I also made no mention of a slip fit on the bearing side of this piece I will machine, I planned on making that a press fit, with the inside diameter of the machined piece as a very tight but slip on fit.
I didn't want to take any chances on cheaper bearings and potentially have one fail at a bad time.

[KDXGarage]

Koyo bearings are great!