The WR450F Clutch Hub "Swiss Cheese" Mod Thread

So back in January, after reading through this thread/post by Thump Me, I pulled my clutch hub and drilled a bunch of holes in it.  Shortly after that, in the "What did you do to your WR today" thread, I said I'd do a write-up but never did.  Well, here we are!


I definitely won't claim to have expert-level knowledge like some guys here have, but the big picture here is to allow more oil to flow through the hub while it's spinning to get more oil to your clutch plates.  This allows more/better oil circulation through the clutch system, which, as I noticed, greatly helped clutch feel.  Take a look at basically any aftermarket clutch hub - Hinson, Wiseco, Rekluse - and you'll notice a lot of additional holes compared to the stock Yamaha hub.  The clutch action basically feels a lot smoother, more accurate, and directly tied to the engine, whereas with the stock clutch hub, there is a bit of vagueness and grabbiness (which I didn't fully notice until after I did this mod and which is also not a word).  


As for ease of electric starting in gear, I didn't have issues to begin with - I've always been able to start even in 3rd gear if I've wanted or needed to (haven't tried a 4th or 5th gear start) - but I have done this and the "79 cent fix" clutch washer mod (here, here, and also here) nonetheless.  What I did notice, though, is that any clutch drag with the engine running, in gear, and stopped with the clutch pulled in is gone completely.  The forward surge and push you get on a lot of bikes when you first click it into gear is significantly reduced.


So here's what the hub looks like from the factory.  You'll notice they drilled six total holes, evenly spaced around the hub, at varying measurements from the base.  This allows a little bit of oil through, but we can do better.






I put the clutch hub in a vise (use aluminum or wood pads - just don't clamp down on the clutch hub with bare steel vise jaws; you'll tear up the hub).  When you need to drill accurate holes in metal, use a center punch first.  Otherwise, you'll drill inaccurate holes.  As for where, specifically on this hub, I went with the ribs that were drilled by the factory (one hole each) and added two fairly evenly-spaced holes on that same rib.  In the next picture, you can see the stock hole behind the punch.  Since all six of the factory-drilled holes are at different spacings and I added two somewhat evenly spaced holes off of those, my little three-hole scheme makes it so each of the drilled ribs around the hub is a little different from the drilled rib next to it.  If that doesn't make sense, don't worry about it - it's not really important.  What is important is drilling additional holes.






Drill away!  I used a cordless hand drill (nice new 20V Porter Cable set I got for Christmas), and a sharp, new bit the same size as the factory drilled holes, which is approximately a 5/32 bit.  It's probably supposed to be 4 mm, but 5/32 is 3.9688 mm and that was close enough for my purposes.






A few shots of brake cleaner and some compressed air cleans everything out.  Then I took a Scotchbrite pad around each hole to smooth out any burring that may have occurred at the edges of the holes on both the outside and inside of the hub.  Clean it all up, and it's ready to reinstall. 






And here we have the finished product.  What I might do differently next time and/or re-do when I have it apart next is drill even more holes in some of the other ribs and valley areas.  I've read about some people drilling holes in precise places - like measured to the millimeter.  That is not important at all unless your OCD is really kicking in.  It doesn't matter exactly where the holes are, just that you add holes in varying places to allow more oil to flow throughout your clutch pack.  I only did even spacing because it made me happy inside.  It doesn't matter.  Just vary the position of the holes to allow for that oil to get to all parts of the clutch pack.  






The result: a smoother, much better feeling clutch that feels more precise, probably stays a little cooler when you're abusing it, probably lasts longer, and should help with the starting in gear issues some people have.  Not bad for zero dollars spent.





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