First step is to remove the belt from the sled.

For a sled without electronic reverse:
Set the parking brake, grab the belt where it comes off the top of the secondary clutch and pull up and forwards (towards the open hood of your sled). This will open the secondary clutch and the belt will slide down into it so it can be easily removed from around the primary (drive) clutch.

For a sled with electronic reverse:
Get the manufacturers supplied clutch tool from your sled's toolbox that screws into the front of the secondary clutch, as it's used to push the clutch sheaves apart. Once the clutch sheaves are far enough apart - you can slide the belt down into the secondary clutch and remove it from the primary clutch. After the belt is removed, you can take the clutch off the sled.

First thing you will want to invest in, or borrow, is a clutch press tool. I have one similar to this SLP model and it has become one of my favorite tools, as it makes working with clutches very easy:

Place the secondary clutch in the clutch press and push the helix down. If your clutches are clean it will slide up and down very easily but the dirtier they are the harder it will be to move the helix. Once the helix is down you will be able to remove the snap ring, or on a SKI-DOO clutch the two half moon clips, on the back of the helix. Then remove the helix and spring. Note how many washers are behind the helix and between the fixed and movable sheave and be sure to keep these in order so the clutches can be assembled again with the washers in the right places.

Removing the circlip.

Next you will want to clean the helix. Some models have helix that have a coating on them and you will want to be careful to not damage it. This helix doesn't have any coating so it's very easy to see the dirt on it.

Cleaning the dirt and grime from the helix will increase the responsiveness of your ride.

The helix is a very important part of the clutches because all of the power that is created by the motor will be applied to the secondary clutch via the buttons, or possibly rollers. Assuming that you are going to use the helix you removed from the sled you will want to clean and polish the helix ramps to a mirror-like shine so your clutches can react as quickly as possible. The outer surface of the helix should also be cleaned and polished to aid with this. Note: if you are installing a clutch kit that contains a helix you don't have to worry about cleaning the stock unit.

Next, clean the inside of the movable sheave. This will include taking any belt dust off of it and any grease that is on or around the brass bushing on the sheave. Once it's cleaned, inspect the large bushing on the outside of the movable sheave. It's a copper bushing with a coating on it and if you're seeing more copper then coating it's time to replace. To replace it, remove the screws that are holding the bushing in. Then use a brass drift to knock the old bushing out. Clean the surface and then pound the new bushing in and replace the screws. If your clutch has a set of buttons inside it (as opposed to rollers) you want to inspect them for wear as well. If they are worn down use a set of long nose vice grip pliers to pull them free.

Using pliers to remove the buttons.

They can be brittle, and if they break off while pulling them out then insert a small wood screw, (#4 1" long work well) and then pull them out by the inserted screw

Use a small woodscrew to help remove problematic buttons.

Springs are wear items, like belts or brakes on a car, eventually they will need to be replaced. A good rule of thumb is to replace them every 3 years or 3,000 miles. Sacked-out springs will impact performance so this is the first place I turn to after inspecting the belt. Worn out springs make your sled feel like it's stuck in high gear all the time, so it won't have as much power and snap as it should. The easiest way to check the spring is to measure its free length (un-installed length) from charts available from the spring vendor. The springs in older style clutches tend to have tines or ears on them and if they don't align then that's another sign that the spring needs to be replaced.

If the tabs on the spring don't align it's time for a new spring.

Before assembling the clutches you wan to lightly grease the shaft on the fixed sheave. This will allow the movable sheave to easily slide up and down on it while you're riding the sled. Once you place the movable sheave on the shaft, check to see if it binds. If it does, that will affect performance and the sheave will need to be sent out to have the bushing replaced.

Assembling with a spring without tabs:
Place the movable sheave on the shaft of the fixed sheave; slide the spring and helix onto the shaft. Rotate the helix so the keyways in the helix and shaft align and push the keyway in. The place the proper amount of washers onto the back of the helix and install the snap ring or half moon retaining clips.

Assembling with a spring with tabs:
Place the movable sheave on the shaft of the fixed sheave and then install the spring. The spring has to be inserted through the hole in the movable sheave and then into the hole in the helix. Some helixes have a few different holes where the spring can be locked in, use hole #2 as a starting point. Rotate the helix so the slots in the helix and shaft align and then push the key in to align the helix to the stationary sheave. Start to push the helix down into the movable sheave but leave it up about half an inch. Rotate the movable sheave counter clockwise 1/3 of a turn to place a torsional preload on the spring. Then push the helix down into the clutch an install washers and the snap ring or half moon retaining clips.

The helix gets locked to the stationary shaft via the keyway.

Clean clutches are more efficient, shift better and run cooler.

Clean the clutch faces with acetone to remove all grease, oil or other contaminants and then install the clutch into the sled. Wrap the belt around the primary clutch. If you used a small clutch tool to remove the belt, install it now and install the belt. Otherwise rotate the movable sheave 1/4 turn and push the belt down in between the clutch sheaves. This will create the length in the belt so it can be spun around the rest of the secondary clutch. When installing the belt be sure to install the belt so you can read the numbers off it.