In the Willamette valley sweet cherries ripen starting in early June and running through mid-August, depending on variety. Considering how cold this spring has been, it is likely the green cherries need a little more time to ripen up. Trees that have been neglected can lead to smaller sized fruit.

One other possible cause, both little cherry virus and X-disease
cause small, tasteless, bitter fruit. In both cases, the fruit turns color as it ripens, but it tends to be lighter in color than normal fruit.

It sounds like your fruit is still green and hasn’t ripened yet. To restore a neglected tree, prune the tree to remove any dead, diseased, or dying limbs, and to open up the tree. Water your tree weekly during the dry days of summer. Avoid overhead irrigation, if possible. It can lead to disease issues. A little fertilizer would stimulate new growth as well.

Refer to OSU Extension publications Growing Tree Fruits and Nuts in the Home Orchard and Managing Diseases and Insects in Home Orchards for more general maintenance and pest management tips.