When a bore comes out oversized, pressing in a thin-walled bushing can save the part. The process involves boring the damaged hole to a larger diameter, pressing in a bushing, then boring or drilling the bushing to the original size. I have used this technique on hydraulic cylinder barrels, pneumatic valve bodies, and machine tool housings. It is a reliable repair method when done correctly, but the details matter a great deal. ...
Understanding Oversized Holes and Bell Mouth Oversized holes and bell mouth are two related but distinct quality problems. An oversized hole is uniformly larger than the drill diameter along its entire length. Bell mouth is a local enlargement at the hole entry that tapers to the correct diameter deeper in the bore. I have seen both problems on the same part. The entry is 0.1mm oversized from bell mouth, and the rest of the hole is 0.03mm oversized from drill runout. Each problem has a different root cause and a different fix. ...