Hello Johnny RPH,

Thank you for the feedback.

When the lawn is being cut uneven, this can indicate a few different things. The first being that the lawn itself is rough or uneven. However, if this is not the case then it is possible that the grass is too tall, or the cutting height is set too low for the type of grass. Try raising the cutting height and reduce walking speed in order to allow for a more effective cut and a proper discharge of the clippings. For a healthy lawn, always cut off one-third or less of the total length of the grass. The average lawn should be approximately 1 1/2 to 2” (3.8 to 5 cm) long during cool months, and between 2" to 3 1/4" (5 cm to 8.3 cm) long during hot months. If you have tried these suggestions, try having a look underneath of the mower deck and ensure that there has been no damage to the motor shaft, fan, blade, blade washer/insulator or the bolt. If any of these parts have been damaged or thrown off balance this will result in an even cut and likely, a noticeable vibration while in use.
Lastly, regarding the blade. If the deck size is 21" the blade will likely be 20" to allow for blade rotation.
Should you require further assistance, please contact Greenworks Pro toll-free helpline at 1-855-345-3934.