Technical Notes

Cylinder Hones

HONING is the finishing of a bored metal part by means of rotary motion using an abrasive cutting stone or stones.

Photo: cylinder hones.The ideal finish is a series of scratches at about 30 to 45 degrees criss-crossing each other in the bore. This assists in retaining oil on the cylinder walls and thus improves lubrication, performance and cylinder life. Because of the action of the stones, bores tend to become rounder and it is possible to remove up to 1 thou per inch taper.

These tools seem to work well on most common modelling metals, i.e. cast iron, mild and stainless steel, bronze, hard brass, gunmetal etc.

These hones consist of a central shaft incorporating a flexible section and a spring for adjusting the tension of the stones against the bore side. At the end of the shaft 2 (E 1) or 3 (E2, E3, E4) stones are mounted on a spring-loaded carrier, attached to it at a central pivot point.

Using the Hone

  1. Clean the cylinder bore of swarf etc.
  2. Arrange a supply of suitable lubricant to lubricate the stones and to keep the working surface clear of particles. ideally the honing oil available from us should be used, alternatively a thin oil such as 3 in 1 or a 20/50 motor oil diluted 50/50 with white spirit or kerosene will do. (paraffin or kerosene should not be used on their own). This can be poured or dripped on from a header tank or the part to be honed can be submerged in a container of lubricant so long as it is adequately held.
  3. Either the hone or the job may be rotated to achieve the desired finish; probably the easiest way to do this is with the job still in the lathe. The honing tool is inserted in the bore, spring pressure adjusted (the minimum pressure setting is usually sufficient) and the lathe speed set to provide a surface speed of 275 to 325 feet per minute. (I" diameter at 1145 RPM equals 300 surface feet per minute)The hand held hone is pushed in and out of the bore thus making minute cross-hatched scratches. However, whenever it is the HONE which is being driven it is advisable for safety reasons to greatly reduce the speed to only 100 to 120 RP.M.

    Do not let the pivot point of the stones go beyond the end of the cylinder or the cylinder will be become bell mouthed.
  4. Rinse (white spirit is ideal for this) and check the bore at frequent intervals for size. Ideally the cylinder bore can be 1 to 2 thou undersize before honing, but up to 5 thou can be removed. To facilitate checking bore size a dummy piston can be turned from a suitable piece of bar stock – or better still, use a “stepped” dummy turned full size, 1 thou minus and 2 thou minus.

NOTE: Because of the flexible drive shaft only rotate the hone in a CLOCKWISE direction and do NOT rotate the hone unless in a cylinder bore, and do NOT run the hone at a high speed as this can be dangerous.

Cylinder Hones
Type Description
El HONE (2 stones 1 1/8" long)
Bore Size Range 9/16" to 1 1/4"
E3 HONE (3 stones 2" long)
Bore Size Range 1 9/16" to 3"
E2 HONE (3 stones 1 1/8" long)
Bore Size Range 13/16" to 1 3/4"
E4 HONE (3 stones 4" long)
Bore Size Range 2 1/8" to 7"