Diagnosis
A chain that falls off immediately after tightening almost always indicates improper bar installation, preventing the tensioning mechanism from working. The bar isn't fully seated on the mounting studs, so the tensioning pin cannot engage the hole in the bar. This leaves the chain loose despite turning the adjustment wheel.
How to Fix It
- Fully loosen the two bar nuts (not just a little).
- Lift the tip of the bar up firmly toward the power head to ensure the bar's mounting slot is flush against the bar studs. You should feel it seat.
- While holding the bar in this "up" position, finger-tighten the bar nuts just enough to hold the bar in place.
- Now, turn the tensioning adjustment wheel clockwise until the chain is snug against the bar's underside, with no sag, but can still be pulled around by hand.
- Finally, with the tension set, use the provided wrench to fully and securely tighten the two bar nuts in a crisscross pattern.
If That Didn't Work
Inspect for physical damage. Remove the bar and chain. Check the bar for a warped rail or a worn-out tensioning hole that's become elongated. Examine the drive sprocket for broken or excessively worn teeth. Also, ensure you are using the correct Greenworks/Oregon chain pitch and gauge (likely 3/8" LP .043" gauge) for your model; an incompatible chain will not seat properly.
Heads Up
Chain tension expands when the metal heats up during use. Always set tension on a cold chain. After running the saw for a minute, stop and re-check the tension with the saw off, as it will have loosened and will need a final snug adjustment.