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Unlike some of the other manufacturers, the Yamaha fiche for the R3 doesn't give the standard bearing designation, only the Yamaha part number. All Balls only lists a front wheel bearing kit, so there's no luck there.
 

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I'd be very surprised at the front being 14mm OD as 12/15/17/20 are the standard bearing IDs at the low end of the range. Perhaps that is an M14 nut on a 15mm axle (with 15 being a very common front axle size on smaller bikes)? A slightly smaller nut than the shaft OD is not uncommon (it helps to keep the threads from getting banged up). But sometimes the OEMs do odd things.
 

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I'd be very surprised at the front being 14mm OD as 12/15/17/20 are the standard bearing IDs at the low end of the range. Perhaps that is an M14 nut on a 15mm axle (with 15 being a very common front axle size on smaller bikes)? A slightly smaller nut than the shaft OD is not uncommon (it helps to keep the threads from getting banged up). But sometimes the OEMs do odd things.
Very possible. I read that on a R3 forum and you know how forums are. :)
 

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FWIW, at wemoto.com they call out the dimensions for the R3 axle bearings in their part listing:
93306-20314-00 rear brake side wemoto says 17x40x12 6203
93306-30450-00 sprocket carrier specific to R3 wemoto 20mm x 52mm x 15mm 6304
93306-302X4-00 front 2 each specific to R3 wemoto says 15x42x13 6302

I added the standard bearing number to match their dimensions.
Bending seems to be an issue, and that will need to be addressed by using a stonger steel alloy, possibly with heat treatment, to raise the yield point so the bending stays below the elastic limit. Remember that the steels are basically equally stiff, it is the strength that determines at what point they bend and stay bent.
I saw mention of cryo treatments. What little I've read is that mostly that refines the grain structure, I don't know how much help that can do to acting as a heat treatment to raise the yield and ultimate tensile strength.

"They appear to be gun drilled."
I expect that the OEMs do little to no "gun drilling". More likely on these tubular axles is they start with a tube, swage the threaded end down a bit if they need more thickness under the threads, and then upset the other end to form the nut. They can probably do that much faster than a deep-hole drilling operation.

New axles of better material are probably what is needed, but for one-off/small batch stuff you are unlikely to see the swaging/upsetting processes being used, which means either starting with a much oversize bar and turning a lot of it into chips, or doing something like start with a tube with a thicker wall that lets you cut internal/external threads safely to add a nut/bolt to the end to replace the stock features.

I'm not sure I see a lot of benefit to swapping the N400 axle out for an OEM Yamaha axle that needs periodic replacement because it bends in service.

cheers,
Michael
 

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Discussion Starter · #13 · (Edited)
Michael - Thanks for posing all this! You are probably right about the manufacturing process by the OEM NOT involving gun-drilling. I appreciate your knowledge!

I agree about the cryo treatment being doubtful as a long-term solution to bending. I believe Kood manufactures OEM spec (size wise) replacement axles in Chome Moly. Link to Webike page for the R3 Kood axles.

Link to Kood website where they describe their manufacturing process

If an R3 axle would work, and if it is hollow, I'd probably order mine from Kood/Webike. I may purchase some used R3 parts from Ebay to validate fitment.

Attached are some pictures of an R3 axle for sale on ebay as well as one where I measured the length of a Ninja 400 axle. They look quite similar...

R3:
Cylinder Bicycle part Nickel Recorder Auto part


R3

Ruler Office ruler Rectangle Tool Measuring instrument


Ninja:

Tool Office supplies Font Writing implement Tints and shades
 

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Similar wheels/tires/brakes/chain lines/swing arms make it likely that the axle lengths will be similar too. But of course, Mr. Murphy would probably make sure that the R3 axle is just a bit too short to work. :)

Why not buy the axles Kood lists for the N400 as shown here:


KOOD Front Axle Shaft
MODEL: K-F-019
213.04 USD Save 10.14 USD ( 5% ) Point: 305 pt
KAWASAKI NINJA400 18-21
KAWASAKI NINJA250 18-21
[Material] Chromoly steel (3-layer plating finish)

KOOD Rear Axle Shaft
MODEL: K-R-019
237.05 USD Save 11.54 USD ( 5% ) Point: 339 pt
KAWASAKI NINJA400 18-21
KAWASAKI NINJA250 18-21
[Material] Chromoly steel (3-layer plating finish)

$450 for two axles (which don't seem prone to bending for the N400) might be something that you do after spending money on other items first. Maybe buy some lightweight wheels and brakes and get a larger savings in weight/$ spent?
 

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Discussion Starter · #15 ·
The picture is misleading unfortunately. I emailed with Kood to try to determine the inside diameter and got the following response. I highlighted the disheartening part below.

:confused:




Re: Ninja 400 Kood Axles and Pivot Shaft Questions
Kirk Pierce <[email protected]>
Wed, Sep 7, 2:06 PM (5 days ago)
to 浮田
Thank you. Now I understand.
On Wed, Sep 7, 2022 at 1:28 AM 浮田 和宏 <[email protected]> wrote:
Since normal is not hollow
KOOD is not hollow either.


thank you​


Windows の メール から送信

差出人: Kirk Pierce
送信日時: Wednesday, September 07, 2022 12:08
宛先: 浮田 和宏
件名: Re: Ninja 400 Kood Axles and Pivot Shaft Questions

The axle is hollow, yes?​
How big is the the hole that is drilled in the axle?
Outside diameter is of course 17mm. But what is the hollow (inside diameter) ?

thank you!

On Tue, Sep 6, 2022 at 9:40 PM 浮田 和宏 <[email protected]> wrote:
Thank you for your inquiry.
KOOD axle shaft for 2018 ninjya400 is normal size
Weight is the same.
Please rest assured that you can use it as it is.


KOOD representative Kazuhiro Ukita
 

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Kirk, that is disappointing info from Kood. If the R3 bends the 17mm tubular axle with similar weight and less HP than the N400, it doesn't make a lot of sense to use that OEM part. Unless you can get Kood to give you the grip and threaded lengths on their R3 axle it looks like your next step is to get the cheapest R3 axle you can find on eBay to check lengths/IDs.

Unfortunately, making the ID smaller is adding the metal where it is doing less and less good. But once you know the ID/OD for the R3 you can use that as a "make it stiffer than this" gauge for the N400 axle, unless it turns out the Kood R3 axle will swap in.

Aircraft spruce lists .188" wall as the thickest they stock for .75" 4130 tube. That's an ID of .374". 17mm is .669" so that would be a .1475" wall, or 3.75mm and I'd probably not be too comfortable with that. You'd need 4.5mm wall to match the cross section of a 15mm axle for shear, but you'd have roughly 50% more stiffness than the solid 15mm.

The Kood manufacturing photos showed a long conventional-looking drill bit so it appears they are drilling solid axles instead of starting with tube. You'd probably be looking at something like an 8mm drilled hole, and even with drilling from each end of a 13" long axle that's a very deep hole.

FWIW, the Kawa parts fiche shows AXLE,RR,17X322,M16 though you'd have to verify if that is the entire length under the head or only the unthreaded portion. Yamaha's part fiche for the R3 doesn't give any info. The N400 fiche also shows 6203 drive side (17x40x12), and 6303 brake side (17x47x14) axle bearings and 6205 (25x52x15) for the sprocket carrier bearing. 6004 (20x42x12) is oversize on the OD for the drive side but 6204 (20x47x14) matches on the brake side. You might have to bump the 6205 to a 30mm ID to keep the spacer wall thickness up, but then the OD also goes up so you are looking at reworking both one bearing pocket in the wheel (if there's enough metal) and also the sprocket carrier, which might need to be remade entirely. So there are no easy answers with a bearing swap to use an OEM tubular 20mm axle, and of course you'd have to ensure the larger OD bearings would handle the loads expected to be seen. At least on a track bike you probably don't have to worry too much about subjecting the rear axle/bearings to potholes while carrying a passenger!

cheers,
Michael
 

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SCM435 appears to be somewhat similar to SAE 4135/4137 (which I've never seen mentioned before), basically a variant of 4130 with a bit of nickel and copper added according to the spec sheets.

Since they say they are doing gun drilling, I'll take their word for it. It appears they are making a quality part.

I try to avoid having too many "GRRRAKKA" sounds in the workshop. :)
 

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But if you think a change in material here is going be something even Rossi would feel you’re dreaming. The only way you would ever know the wimpy R3 axel was bent would be when pulling it out to change tires. :)
 
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