The Drive Pulley on the Model 10E and 10ER are a special bore size at 13/16" so it is important to not damage the Pulley or Drive sleeve when separating them. As John recommended
A good soak with penetrating oil and a puller should work. The pulley is cast and fairly fragile so be careful of the force applied.
and I agree with John. Patience can be the key here to a good outcome. Allow the penetrating oil to do its job before trying to use a puller. If your pulley had two set screws holding it on, which is not common, it could be the extra set screw "digging" into the Drive Sleeve that could be keeping it from coming off.
The puller SteveMaryland showed in his post may work fine but I prefer one like the set shown below. Again, these pulleys can be fragile and this type of puller can distribute the pressure all around the pulley edge instead of just three spots. You will also need something to push against since the Drive Sleeve itself has the splined bore. A piece of wood doweling can be helpful here as it will avoid metal to metal contact on the Drive Sleeve and possible damage to the splined bore.
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The above Gear Puller set is an example and you may need a larger puller set than shown to accommodate the 4" step of the Drive Pulley.
