Repair 7

How to Bore a Barrel

Engine cylinder barrels are bored out to a specific diameter when first manufactured. This cavity is precision-cut to fit a matching piston with piston rings. When a cylinder barrel operates correctly all of its parts create a tight chamber for combustion. However, over time the original bore in the barrel becomes warped from repeated friction, heat and cooling. Eventually, the bore loses its tight compression and the engine performance weakens. Re-boring a cylinder barrel helps improve engine performance, although the work is extremely technical.

Instructions

1

Obtain a bore gauge tool. Position the cylinder barrel on your workbench or work area so it wont move.

2

Use the bore gauge to measure the current bore from 12 oclock, 6 oclock, 3 oclock and 9 oclock positions. Record these measurements.

3

Apply a honing plate to the bottom and top of the cylinder. Tighten it down with the barrel hardware and a socket torque wrench. Use the torque setting to ensure the appropriate tightness. Remeasure the bore from the same four positions as in Step 2. Write them down.

4

Compare the differences in the bore measurements to determine the change due to tightening pressure on the cylinder metal.

5

Loosen the barrel and install it on a drill press table. Secure the barrel upside down so the bore goes from the bottom to the top of the cylinder cavity when you drill. Obtain a metal bore drill bit for the new size desired based on your measured data.

6

Install the bore drill bit into the drill part of the drill press. Lock it in tight. Line up the drill bit position at dead center on the cylinder. Turn on the drill press. Lower the drill press mechanism slowly but firmly until it drills out the new bore in the cylinder. Remove the drill bit by rotating the drill bit upward again.

7

Remove the barrel and prepare it for honing and chamfering of the ports to remove the new sharp edges.