Need 4 stroke help...yz426/yz450f

I will be the first to admit, Im new to the 4 stroke world. I have owned 2 strokes all my life, and I never wanted to own a 4 stroke, until I needed too a few years ago. Long story short, I have never had one open.

now, My quad is a aftermarket Honda chassis, with a yz426f motor with a Athena 444 big bore. I have the motor out of my quad, sitting on the bench to finally replace my 5th gear shift fork I bent 3 years ago, and here is where I get confused…

I know the top ends on the wr400/yz426/yfz450 are all interchangeable. My motor, being a 02, I am not sure if the shift forks/transmission gears are year specific. Basically, Im wondering if 01 yz426f shift forks, will work in a 02 motor? everywhere I look, it just says 01.

I also am aware that there are a few years that the yz450f dirtbike motor was a 4 spd. I wouldnt mind making my 426f based motor a 4 speed. It has the power to pull it, and my gears would be longer…Can I do this?

i know on mine the trans was all diff as i sheared my forks once . and it was a 01 426 . the only changes i made was using a 450 exh cam on it . if i remeber right most of the diff was in the case where the shafts set it and so on

I know that the 01 transmissions had problems, and were weaker then the 02’s. I am just wondering if they use the same exact shift forks. I only need the 5th gear shift fork, as my 1-4 shift flawless.

I made a post on exriders. I am really curious on switching to a 4 speed.

ya may need to do the whole lower , like i said the cases are diff between yrs . just get the hardened shit i did and i never had a prob again . ill try and remember where i got my shit thru . it wasnt exp and had it all quick

Im not in a hurry to get the parts really. I still need to order swingarm bearings and a new swingarm bolt. When I went to take the motor out, my swingarm bearings where shot and fused to the bolt, so I had to cut the bolt out. Sucks thats its a $50 bolt lol