KX Fork Conversion / Required Knurling?

Questions and comments about converting to beefier forks..

KX Years on required knurling (Only vote if "YES")

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Total votes: 37

Bigdavelittle
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KX Fork Conversion / Required Knurling?

Post by 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.
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KX Fork Conversion / Required Knurling?

Post by 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 TREES944
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KX Fork Conversion / Required Knurling?

Post by 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.
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Re: KX Fork Conversion / Required Knurling?

Post by 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.
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Re: KX Fork Conversion / Required Knurling?

Post by 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!
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Re: KX Fork Conversion / Required Knurling?

Post by 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.

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.
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Re: KX Fork Conversion / Required Knurling?

Post by 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!
'97 KDX220R - purple/green! - KLX forks, Lectron, FMF, etc, '99 KDX220R awaiting rebuild & mods, '77 Suzuki PE250 & '83 Suzuki PE175 Full Floater restomod projects, '77 Suzuki GS750-844cc, '77 GS400-489cc racer project, '62 GMC 1000 Panel Truck, '88 Suzuki Samurai TDI/Toyota swaps, '88 Toyota 4x4 pickup
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Re: KX Fork Conversion / Required Knurling?

Post by 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.
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Re: KX Fork Conversion / Required Knurling?

Post by 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. :-)
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Re: KX Fork Conversion / Required Knurling?

Post by 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 threadlocker, I doubt anyone would have trouble with a knurled stem.


SS109, I was checking out the RM125 steering stems, which look just like some Suzuki GSXR steer bike stems I have as well as V-Strom stems I've browsed for street bike fork swaps into vintage Japanese bikes. On the conventional 49mm Showa RM fork triple clamps, I think I can just chuck the triple into a lathe and cut the step off the bottom of the triple as it has a cast in step that rises up a good 8mm or so above the triple before the bearing seating area.
I just checked, and all of the RM 2-stroke Showa fork's triple clamps through 2006 have this raised step on the lower triple, so they all should be able to be machined down slightly to lower the ride height and fit them into the KDX frame's head tube as described below.
Image
I think I can just cut this down to almost nothing, which also lowers the ride height increase of the KDX's new fork swap, and cutting the stem back to the same press fit o.d., and then run the aluminum stem RM125/250 Showa fork's triples direct into the KDX frame.
Although the necessary 30x47x12 upper bearing would be riding 3.5mm into the threaded portion of the stem approximately if ran with a 3mm spacer under it to be at the top of the KDX frame's bearing pocket to keep the top of the bearing flush with the frame's top, or else run it down in the frame and use a 30.01mm i.d. spacer above the bearing 3mm thick to take up the slack, probably the more appropriate solution considering the threads location and 12mm tall upper bearing vs 15mm original. I'll have to look and see if the later Showa 47mm inverted forks have a similar raised step portion on the lower triple bearing seating area that could be shaved off to stretch out the stem to near KDX dimensions.
Last edited by Chuck78 on 12:25 pm Sep 15 2022, edited 1 time in total.
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Re: KX Fork Conversion / Required Knurling?

Post by 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. :-)
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Re: KX Fork Conversion / Required Knurling?

Post by Chuck78 »

KDXGarage wrote: 01:58 am Sep 15 2022 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.
'97 KDX220R - purple/green! - KLX forks, Lectron, FMF, etc, '99 KDX220R awaiting rebuild & mods, '77 Suzuki PE250 & '83 Suzuki PE175 Full Floater restomod projects, '77 Suzuki GS750-844cc, '77 GS400-489cc racer project, '62 GMC 1000 Panel Truck, '88 Suzuki Samurai TDI/Toyota swaps, '88 Toyota 4x4 pickup
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Re: KX Fork Conversion / Required Knurling?

Post by 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. :-)
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