[bennyrides]

Thanks to @GoFaster, now I know which piece I broke:
Fork Tube Check Valve
and that sounds better than what I labelled it as.

I broke it when I was attempting to slam together the valve body (like an idiot), thereby with crushing force - chipping off a chunk of this plastic inner fork tube doohickey.

@GoFaster asked for a frame of reference (rightly so); the pictures below are the inner fork tubes, upside-down, where the plastic bottom-out sleeve is inserted. Just above the outer lip, the lower slide bearing clamps to a machined slot on the outer fork tube.

 

[airhead83]

I have a schematic with part numbers below for the 2016 R3. Since I'm not which part it is, I won't guess... but the front fork tubes appear to have plenty of replacement parts. Maybe this will help. The part #s are Yamaha OEM #s, and will be the same from any reputable vendor. Good Luck.
Yamaha OEM Motorcycle Parts | MotoSport

 

[bennyrides]

Unfortunately, there are no parts on that schematic which appear to fit. I believe the part is a permanent placement inside the tube-end which is often the part that is removed when modifying the fork tubes for use with a complete cartridge kit.

 

[bennyrides]

I've confirmed, this route is not functional; 41mm fork tubes from other bikes will not necessarily fit, just because they're the same length and diameter.

Order non-OEM parts at your own risk.
You must ensure:

• Inner diameter (i.d.) is the same as the stock fork tube
• Fork tube cap has a similar depth as an OEM fork tube
  • This may mean the depth of another tube will change the metrics for your fork suspension
  • You may be required to buy a cap that fits the tube you buy, specifically
• Bottom-out cone fits in the bottom of the fork tube

All-in-all - this route is not recommended (but I left it in the spoiler below for the record).

Spoiler: Confirmed: This fork tube does NOT fit

I ordered a 41mm Harley FXST fork tube; the inner diameter is too narrow for Yamaha R3 parts to fit inside. As such, these fork tubes are also heavier than Yamaha R3 fork tubes.

Getting desperate to order a 41mm fork, and them being on back-order from the major retailers, I've found this nifty (possibly compatible) list of 41mm forks on ebay (Item location "North America" and "Buy it Now" filters selected).

If it fits, it's a steal at $129.09 shipped
Always try to order a part that is being stored near you to reduce shipping costs & time. Refer to the Item Location choices on the left sidebar.

Also, it's important to match dimensions and (in this case) where the slide bearings are placed (see picture below).

• 
  
• 
  
• The GoFaster Way
• As @GoFaster pointed out in his response (yes, I'm assuming he's a man), a step in the process of ordering generic parts as replacements is to ensure both parts are identical before reassembly.
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• In this case, he made me aware that I broke my R3 fork tube's check valve, and that I should ensure this piece is intact and within the same location & dimensions as the R3 fork tubes.
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• I will post here again when I receive the fork tube.
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• Extra Rant
• Confirmed: this HardDrive fork tube for Harley FXST is about an inch deeper than Yamaha R3 tube caps
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• The caveat is this: I don't know if the top caps will screw into these fork tubes. The information on "Harley FXST/FXDWG fork tubes" is unlikely to discuss the threading and depth of the top cap; I will just have to wait and find out.
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• This may lead to the discovery to a solution for the Ninja 650 rear shock rear end lift of an inch (thereby invoking a forward-rake when installed on the R3)... Here's a term I never heard of before googling "Harley FXST/FXDWG fork tubes": "fork tube extensions". To read more about this little experiment, refer to my post on the cheap suspension upgrade guide.

 

[GoFaster]

I don't have a frame of reference for where your two photos were taken from. Are those looking down the end of the (inner? outer?) fork tube? Is that view looking up into the bottom of the inner (upper) fork tube of the conventional (non-inverted) forks of a 2015-2018 model, through which the damping rod slides?

If it is what I think it is, one of those bits in the photo - not sure if the beige-coloured plastic piece of the (blue?) piece underneath it - wiggles up and down relative to the fork tube, because that's the check valve which bypasses fluid when the fork is compressing.

And if that's the case ... make sure your aftermarket fork tube actually contains that part and isn't simply a bare tube to which you're expected to transfer those bits and pieces into.

OR ... Use this as an excuse to upgrade to a fork cartridge kit. Ohlins, Ktech, Adreani (sp?), take your pick, at which point, that piece no longer matters.

 

[bennyrides]

...make sure your aftermarket fork tube actually contains that part and isn't simply a bare tube to which you're expected to transfer those bits and pieces into.

OR ... Use this as an excuse to upgrade to a fork cartridge kit. Ohlins, Ktech, Adreani (sp?), take your pick, at which point, that piece no longer matters.

Understood. You have a good point that I wasn't 100% clear on when I wrote about ordering a replacement.

I added your responses to the original posts; for clarity.

 

[GoFaster]

You may also find that little valve assembly to be called a "base valve" (because it's in the "base" - bottom - of the fork leg) or the "foot valve" (similar logic).