help changing fork springs

I have a 2011 YZ450F. I need to change out the stock springs ones that are for my weight. I have never done this before and scared to screw anything up. I have read my manual, and it is very vague, I want to hear from those folks that have changed there fork springs out often, and what advice you can give me before I attempt to do this on my own. I have changed rear shock springs before, and that is easy to do.

There are also so many different oil weights for the front fork. I was thinking about going with a 5 or 7w. I'm also 238lbs without gear if that helps.

What tools will I need to complete this job? I will need new fork oil I believe, and a fork cap wrench(?), I can't make out fro the diagrams in my manual, but it looks like the spring is at the bottom of the fork tube? Could I just take the bottom cap off, slide out the old spring and slide in the new one?

Thank you all for your time. I look forward to tackling this and learning something new.

At minimum, you'll need a 49mm 8 point wrench for the fork "caps". A 50mm will work. "Caps" is in quotes because the cap is actually the top of the fork cartridge assembly. You'll also need a rod holder, which you can make out of any piece of metal about 1 1/2" wide by cutting a 1/2" wide slot an inch or so long in one end of it. If all you want to do is change the springs, and you don't want to open the cartridge itself and change that oil, the simplified method goes like this:

  1. Lower each fork tube in the clamps far enough that you can get the cap wrench between the top clamp and the top of the fork. Snug the lower clamp in this position so it will hold the fork for you while you loosen the cartridge in the top of the fork. Then remove the fork from the clamp. You do this so that you don't have to find something to try to clamp the fork in on the bench that won't scratch it while you loosen the cap. You can also remove the bar mounts, loosen the top clamp and then loosen the caps, but that's too much work.
  2. With the fork off, unscrew the cap/cartridge from the top of the fork, slide the tube down a ways and dump the oil out.
  3. On the bottom of the fork, turn one of the rebound adjusters all the way in, counting the clicks. Make a note as to how far out it was so you can repeat the setting when you reassemble. Back both rebound adjusters all the way out until they stop.
  4. Remove the rebound adjuster from the bottom of the fork, compress the outer tube until the rod is exposed, and slide the rod holder in place.
  5. Loosen the lock nut and remove the adjuster from the rod
  6. Turn the fork back over (more oil will come out the bottom) and pull the cartridge assembly out. The spring will now slide free.

The manual makes some references to a gap between the lock nut and rod that must be observed when reassembling. These are confusing at the very least because of the sketchy translation it got. Read this post to clear that up:

http://www.thumpertalk.com/topic/680824-base-bolt-jam-nut-clearance-06-yz-450-fork/page__view__findpost__p__6860151

When you're done, add back the oil for the outer chambers and you'll be all set.

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