Cures for a Glazed Bore

Written by tony oldhand
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Cures for a Glazed Bore
Internal engine parts must have different finishes from mirror smooth to satin. (car engine image by itsallgood from

Internal parts of a car engine must have different finishes. Some parts, like the crankshaft, must have a mirror-smooth finish. The inside of a cylinder, however, must have a satin finish. Over time, the satin finish becomes polished mirror smooth due to the constant rubbing by the piston. This condition is known as a "glazed bore." This is highly undesirable, since all lubrication properties are lost because oil cannot cling to the sides. Simple yet effective techniques will cure a glazed bore, and restore an engine to its former glory.

Hand Honing

To hand hone, first obtain 100-grit emery cloth. Apply 30-weight engine oil to the inside of the cylinder. Fold a piece of rag about four inches by four inches square. Place the rag over the emery cloth. Start sanding the inside of the piston. The direction of sanding is critical. Start from the top, and twist your hand about one half turn as you are going down the cylinder, like you're trying to cut rifling grooves in the barrel of a gun. Repeat, turning your hand the other way. The end result is a cross-hatch pattern cut into the cylinder walls, with a satin finish. The University of Michigan recommends the lines intersect at 22 to 32 degrees (see reference 1, page 63). Hand honing is very tedious, but is a better method over machine honing on a rare engine. The object of the game is to remove the glaze, without removing metal. Machine honing is quick, but removes metal in the process.

Honing Stones

Drill-mounted honing stones are readily available at any auto parts stores. This is a device that has two or three stones mounted on a spring-loaded framework. First, mount the frame in your drill. A variable-speed drill is highly recommended, since you can control the speed of cutting. Apply oil to the cylinder. Collapse the framework of the honing tool, and insert it in the cylinder. Start your drill at the slowest speed, and work the hone in and out of the cylinder. If honed correctly, you should end up with a cross-hatch pattern.

Bottle Hone

A bottle hone is a recent development. It looks like a large bottle brush, except that it has abrasive ball-shaped stones at the end of the whiskers. The advantage of a bottle hone over a solid stone hone is that uniformity of cutting depth is better with a bottle hone. Another advantage is that the hone does not remove as much metal as a solid hone. You operate a bottle hone in a similar fashion as a solid hone. Start your drill at the lowest speed and work the brush up and down the cylinder as your drill is spinning.

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