Refinishing Cylinder Walls

GENERAL

NOTE: Only experienced technicians should perform this work.

Cleaning
When the cylinder bore is sized and prepared for the piston, wash it thoroughly with detergent and hot water until a light-colored, lint-free cloth wiped through the bore comes out clean. Then apply clean engine oil to the cylinder walls.

Conditions for Honing
^ A cylinder wall taper condition can be corrected through the use of an adjustable (non-flexible) hone.
^ Honing is recommended for refinishing cylinder walls only when no cross-hatch pattern is visible on cylinder walls or for fitting pistons (6108) to the specified clearance.
^ Cylinder walls that are severely marred and/or worn beyond the specified limits should be refinished.
^ If the cylinder walls have minor surface imperfections, but the out-of-round and taper are within limits, try to remove the imperfections by honing the cylinder walls and installing new service piston rings, providing the piston clearance is within specification.

Conditions for Boring
^ If the bore out-of-round or taper dimensions exceed the specifications, then cylinder boring is required.
^ Refinish cylinders that are deeply scored, out-of-round, and/or taper exceeds specification.

BORING

NOTE: Before any cylinder is refinished, all main bearing caps must be in place and tightened to the proper torque so that the crankshaft bearing bores will not become distorted from the refinishing operation.

This operation must be coordinated with piston selection. It is essential to select the pistons BEFORE boring the cylinder block. Then bore according to piston size. If the cylinders do not require boring, the cylinder walls should be prepared for a new set of piston rings by honing.

Procedures
1. Follow the boring equipment manufacturer's instructions for proper use. Allow 0.038 mm (0.0015 inch) for final honing to size and to give a proper crosshatch pattern of approximately 30°.
2. A newly fit piston should have a piston-to-bore clearance of 0.012-0.026 mm (0.00047-0.00102 inch). Oversize pistons and piston rings (6149) are available in 0.25 mm (0.010 inch) and 0.50 mm (0.020 inch) sizes.

HONING

WARNING: DO NOT ALLOW THE HONE TO COME OUT OF THE CYLINDER BORE WHILE IT IS TURNING. THE STONES COULD BE RELEASED AND CAUSE PERSONAL INJURY.

NOTE:
^ Hone only the cylinder or cylinders that require refinishing. All pistons are the same weight, both standard and oversize; therefore, various sizes of pistons can be used without upsetting engine balance.
^ Refinish the cylinder with the most wear first to determine the maximum oversize. If the cylinder will not clean up when refinished for the maximum oversize piston recommended, replace the cylinder block.
^ Before any cylinder is refinished, all main bearing caps must be in place and tightened to the proper torque so that the crankshaft bearing bores will not become distorted from the refinishing operation.

1. Install all main bearing caps and tighten to the proper torque specification.

NOTE: The grade of hone is determined by the amount of metal to be removed. Follow the instructions of the hone manufacturer. If coarse stones are used to start the honing operation, leave enough material so that all hone marks can be removed with the finishing hone which is used to obtain the proper piston clearance.

2. Select the hone grit size. A grit of (180-220) will provide the desired bore surface finish of 18-38 AA.

NOTE: Use a lubricant mixture of equal parts of kerosene and clean engine oil.

3. Set the non-flexible hone to a diameter slightly larger than the smallest cylinder diameter measurement. To finish the procedure you will need to incrementally increase the diameter of the non-flexible hone until a uniform diameter is obtained at the cylinder walls.

NOTE: A satisfactory pattern will be a cross-hatch pattern at an angle of approximately 30° to the cylinder bore.

4. Using a hone speed of 300-500 rpm hone the cylinders.
5. Cycle (up and down one time is a cycle) once per second to produce a satisfactory pattern. Do not hone more than necessary to produce a pattern the full length of the bore.
6. After honing, thoroughly clean cylinder bores with a detergent and water solution and oil the cylinder walls.