put in a new chain but it cuts crooked and pulls to one side. the bar doesn't look bent.

Diagnosis

The "pulling" sensation and crooked cuts on the Ryobi 40V HP Brushless Chainsaw (RY405110) are almost always caused by a disparity in the aggressiveness of the cutter teeth between the left and right sides of the chain. When you install a new chain, it may seem uniform, but manufacturing tolerances or initial "break-in" wear can lead to one side biting deeper into the wood than the other. This creates a lateral force that pushes the bar away from the side that is cutting more efficiently, resulting in a slanted cut even if the guide bar is perfectly straight.

This issue is further exacerbated if the chain is over-tensioned. On the RY405110, the high-torque brushless motor can force a tight chain to "bind" against the bar rails, preventing the chain from seating squarely. To confirm this is the issue, perform a "sight test" by looking at the kerf (the slot created by the saw) from the end of the bar; if the gap is wider on one side than the other, you have a tooth imbalance. Additionally, check for "burrs" on the guide bar rails—small metal shards that can deflect the chain's path as it travels.

How to Fix It

To correct the tracking and ensure a straight cut, you must balance the cutting edges of the chain using a precision filing method.

1. Prepare the Saw: Remove the 40V battery and engage the chain brake to ensure the saw cannot accidentally engage. Set the saw on a stable workbench.
2. Identify the "Strong" Side: Determine which side is pulling the saw. The saw will pull away from the side that is cutting more aggressively. You will be filing the teeth on the side that is cutting "too well" to bring them down to match the weaker side.
3. Select the Correct File: Use a 5/32" round file, which is the standard for the 3/8" low-profile chain used on the RY405110. Use a file guide to maintain a consistent angle.
4. Set the Filing Angle: Position the file at a 30-degree angle relative to the guide bar. Ensure the file is level horizontally so you don't create a "hook" in the tooth.
5. Execute Balanced Strokes: Apply 2-3 firm strokes to each tooth on the "strong" side. Do not over-file; the goal is to remove a tiny amount of material to equalize the bite.
6. Check Tension: Loosen the bar nuts slightly and adjust the tensioning knob until the chain fits snugly against the bottom of the bar but can still be pulled freely by hand. Over-tightening the chain on this model causes excessive friction and increases the likelihood of pulling.
7. Test Cut: Make a shallow test cut in a scrap piece of soft pine to verify the bar is now tracking straight.

If That Didn't Work

• Inspect the Bar Rails: Use a fine-tooth metal file to remove any "burrs" or rolled edges from the sides of the guide bar rails. If one rail has a burr, it creates uneven friction, which mimics the feeling of a chain pulling to one side.
• Verify Chain Seating: Remove the bar and chain entirely. Clean the drive sprocket area of all sawdust and pitch. Reinstall the chain, ensuring it is seated perfectly in the drive links of the bar. A chain that is slightly "off-track" in the groove will cause erratic cutting.
• Check for Bar Warp: While the bar may look straight, place it on a known flat surface (like a granite countertop or a machinist's table). If there is any daylight between the bar and the surface, the bar is warped and must be replaced.
• Replace the Chain: If the chain was a low-quality aftermarket replacement, it may have inconsistent heat-treating. Replace it with a genuine Ryobi 16-inch low-profile chain to ensure uniform tooth geometry.

Heads Up

• Tensioning Warning: Never tension the chain while the bar is under load or tilted. Always ensure the bar nose is resting on a surface to prevent "over-tightening," which can warp the bar or damage the brushless motor's drive gear.
• Lubrication Check: Ensure the automatic oiler is functioning. If the bar runs dry, the metal expands from heat, which can cause the chain to "drift" or pull to one side as the friction increases.
• Cleaning the Sprocket: Every 5-10 batteries of use, remove the side cover and clear the debris from the drive sprocket. Clogged sawdust here can cause the chain to enter the bar at a slight angle.