Cylinder Bore Refinishing
Cylinder bore refinishing is extremely important in the engine rebuild process. There are some basic rules and facts which will prevent common problems incurred when deglazing or refinishing cylinders.
CROSS HATCH ANGLES
The correct angle for cross hatch lines to intersect is approximately 45°. Too steep an angle promotes oil migration down the cylinder resulting in a thin oil film which can cause ring and cylinder scuffing.
Too flat a cross hatch angle can hold excess oil which conversely causes thicker oil films
which the piston rings will ride up on or hydroplane. Excessive oil consumption will result.
The diagrams will illustrate cross hatch angles.
Two basic systems are used to refinish cylinder wall either rigid stones or a flexible brush.
Correct cylinder finishes can be achieved with either system if used correctly. In all cases the manufacturers instructions must be followed with respect to :
- Stone grit
- Honing oil
- Stone pressure (Automatic equipment)
The vertical speed of the brush or hone in the cylinder is what causes the cross hatch angle on the surface of the cylinder wall Too slow a vertical speed causes too flat an angle while too rapid up and down motion of the hone or brush causes too steep an intersecting angle. In the case of hand honing it will be necessary for the operator to experiment to learn the proper up and down movement in relation to the rotating speed of the one to produce proper cross hatch angle.
Substantial controversy exists on the correct cylinder roughness for proper seating of piston rings whether chrome moly or plain cast iron It has been our experience that the use of 220/280 grit stones and achieving proper cross hatch angle produces a finish compatible to all three types of the above rings
The single most critical factor of any cylinder refinishing job is the cleaning of that cylinder after the honing operation
It can be stated pistons rings and cylinder bores will forgive slight variations in roughness cross hatch angle etc. No engine component will tolerate dirt!
Honing cylinders leaves two types of “dirt” on the cylinder wall, honing stone residue and cast iron dust If not removed before the engine is reassembled the worlds finest lapping compound is waiting to destroy all the hard work of assembly the instant the engine is started.
Proper cylinder cleaning consists of a thorough scrubbing of the block with hot soapy water taking care to clean the surface under the cylinder facing the crankcase Rinse with hot water dry and lightly oil to prevent rust
For detailed honing questions it is wise to contact the manufacturer of your specific equipment They are experts in metal finishing and of course completely understand their own equipment
In general if the foregoing practices are used excellent engine performance will result