Force custom avatar in Top Admin Bar instead of Gravatar

Locate folder/file : WP-INCLUDES / ADMIN-BAR.PHP .
Search for “howdy”.
Replace the line before where says $avatar.

/* translators: %s: current user's display name */
//$avatar = get_avatar( $user_id, 001 );
$avatar = "<img alt='' src='/wp-content/uploads/YourAvatar.jpg' class='avatar photo' >";

To fix the big avatar on mouse hover, in the same file search for $user_info = get_avatar and edit the line like this:

//$user_info  = get_avatar( $user_id, 64 );
$user_info = "<img alt='' src='/wp-content/uploads/YourAvatar.jpg' class='avatar photo' >";