Arithmetic average of all profile values of the roughness profile | Kolbenschmidt | BF | Motorservice

Testing of honing results

Testing options and display of optimum honing parameters

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Information on diagnostics

Honing is a fine machining/manufacturing process for almost all materials. It can be used, for example, on piston sliding surfaces for cylinders in combustion engines. The tool used is known as a honing stone, which rotates and moves along the longitudinal axis. The resulting surface can be recognised by the cross-hatch finish. But how do you measure the results of the honing process on a workpiece, and how do you assess the surface or shape? Are there any optimum honing parameters? This article outlines various testing and evaluation options for assessing the surface quality (surface roughness) and roundness deviation in the cylinder.

Assessment options

Roughness tester

Roughness tester | Kolbenschmidt | BF | Motorservice
A qualitative, reliable statement about the roughness of the surface can be made using a roughness tester. Through the distribution and definition of the peaks and valleys (topography) in the roughness record, an assessment can be carried out as to the development of the surface during running-in, along with how much oilretaining volume is provided and how high the contact ratio will be. Furthermore, the roughness record provides valuable documentation of the honing quality.


Microscope | Kolbenschmidt | BF | Motorservice
The surface structures can also be assessed visually using microscope images. From 200x magnification, the honing angle, profile depth and the exposure of the silicon crystals can be assessed more easily. Unintended dirt deposits or peak folding formations become visible.

In addition to the roughness record and the measurement report, microscope images are a good method of visualising and documenting the quality of the honing process.

Bore measuring device with dial gauge

Bore measuring device with dial gauge | Kolbenschmidt | BF | Motorservice
For a quick assessment of the cylindricity it is sufficient to determine the diameter at several points and thereby gain an idea of the resulting cylinder shape. Basic out-of-roundness in the cylinder can also be determined using the bore measuring device with dial gauge (Subito) using spot-based measurements. The number of measurement points determines the accuracy of the results regarding the shape.

The majority of the cylinder shapes shown below can be determined using the bore measuring device with dial gauge.

Assessment of the surfaces

Measured value   Description  
Mean roughness Ra Arithmetic average of all profile values of the roughness profile
Individual roughness
Rz1 Sum of the height of the
largest profile peak and the
depth of the largest profile
valley of the roughness
profile within a sampling
length (lr)
Roughness depth Rz Arithmetic average of the
individual roughness
depths Rz1 of successive
sampling lengths
  Rmax Largest individual
roughness depth within
the entire sampling length
Core roughness depth Rk Depth of the roughness
core profile
Reduced peak height Rpk Average height of the
peaks projecting out of the
core area
Reduced profile depth Rvk Average depth of the
valleys projecting out of
the core area
Material ratio Mr1 Smallest material ratio of
the roughness core profile
  Mr2 Largest material ratio of the
roughness core profile

01 Profile peak surface
02 Core area
03 Profile valley surface
04 “Peak area”
05 Material ratio curve (Abbott-Firestone curve)
06 “Valley surface”
07 Material ratio
Based on the parameters, in the series production of each engine type the best honing parameters are determined in order to achieve the optimum when it comes to friction, wear and the resulting oil consumption of the surfaces. During reconditioning, more simple and widely applicable machines often result in limits. Despite this, high-quality cylinder surfaces can be created if you pay attention to the important parameters. The table should provide assistance in this regard.
Measured value   Unit Recommended values
Sensing length: 4.8 mm / Sensing tip: 2 μm / 90°
      Petrol / diesel
passenger car
Diesel utility
Arithmetic mean
Ra μm 0.15 to 0.40 0.30 to 0.50
peak height
Rpk μm 0.10 to 0.40 0.20 to 0.60
Core roughness depth Rk μm 0.20 to 0.60 0.50 to 1.50
profile depth
Rvk μm 0.50 to 1.00 0.50 to 1.50
material ratio
Mr1 % 4 to 12 4 to 10
material ratio
Mr2 % 75 to 90 80 to 90
Honing angle α ∠° 25 to 45 40 to 60

Assessment of shapes and geometries

Type of fault     Reason for fault Remedy
Out-ofroundness Stage 0:
Perfect cylinder
Correct geometry  
  Stage 1:
Due to stuck honing head Check the freedom of movement
of the honing head
  Stage 2:
Oval cylinder
Caused by deformation and
Reduce the cutting pressure –
replace the honing stones
if necessary
  Stage 3:
Triangular out-ofroundness
Results from distortions
from stage 2 and 4
For remedies,
please see stage 2 and 4
  Stage 4:
Square-shaped faults
Usually caused by
distortions resulting from
the tightening of the cylinder
head bolts
Reduction in distortion by using
a torque plate
Trumpet, cone and funnel shapes     Caused by the incorrect
stroke position. The stone
overrun is too large on the
side with the larger diameter
Correct the stroke position –
reduce the stone overrun /
use shorter honing stones
Barrel shapes     Caused by honing using too
little stone overrun/honing
stones that are too short
Increase stone overrun/use
longer honing stones
Ripples     Caused when extremely
short honing stones are
used for honing, or when
trying to remove narrow
points by dwelling on the
area with the honing head
Longer honing stones, short
strokes for the targeted
processing of narrow points