I've found a few posts on this but nothing definitive, maybe it's just poor search skills, dunno.... I'd like to put a YFZ450 clutch in my 2005 WR as I'll be doing some long rides on it, including some bitumen, and the YFZ clutch has springs in the driven gear assembly to soften impact on the gearbox. And it's MUCH cheaper than a cush hub, cheap enough to do just as a precaution.. Others have done it successfully apparently, but I recall reading that the primary drive gear from the quad needs to be swapped in as well. From some reading on Yamaha part numbers, it seems the 1st part is the bike model, 2nd part is part number, 3rd part is revision (but will fit older versions with same part number), and last part is colour. A check on part numbers at partzilla gives this: 2005 WR450 clutch basket 5XD-16150-20-00 2005 YFZ450 clutch basket 5TG-16150-00-00 So it's different, but they are interchangeable. 2005 WR450 primary drive gear 5TJ-16111-00-00 2005 YFZ450 primary drive gear 5TG-16111-00-00 This suggests the drive gear is the same? If someone has actually done this can you let me know if the primary drive gear needed to be changed?