Rottler HP 7A - Limited over Travel and Blind Holes; Cross Hatch Angle; Honing in General; Large Amount of Material Removal

Section 5 Operating Instructions HP7A Manual
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5-3
Limited Over Travel and Blind Holes
A problem with stock removal with hone heads exists on many of today’s blocks and cylinders. It may be
necessary to relieve bores with a die grinder, portable grinder or boring bar.
Cross Hatch Angle
Desired Cross Hatch Angle can be achieved by activating the AUTO CROSS HATCH button. You
have to input the angle desired, the bore size, and the bore length. This can be done while the hone is
operating or can be set by accessing the MACHINE SETTINGS screen. There is also a CROSS HATCH
CALCULATOR button that will access built in calculator that can be used to make calculations using
different values.
Honing In General
The HP7A is capable of honing a cylinder very accurately with very little or no work from the operator.
The goal of the operator should be to set the Upper and Lower Stops correctly, select the proper stone
length, and honing pressure that will allow the machine to hone the cylinder to size.
While the HP7A is running, pay attention to the load graph display (left on the control screen). The load
display measures the actual motor load and displays it in percentage of rated motor current. As the HP7A
is honing, the control takes current measurements from the motor throughout the length of the cylinder
and displays them with solid red colored bar the approximates the shape of the cylinder wall. The farther
the bar moves to the right the smaller the bore is in that area. For example, if the bar near the bottom of
the display moves farther to the right than the rest of the bar, it means the bottom of the bore is a slightly
smaller diameter near the bottom. The same would be true for the top and middle of the bore.
Large Amount of Material Removal
When you have large amounts of material to remove from a cylinder (.005 and up) the following steps
should be used to maintain size control.
For stock removal of .010 or more it is best to use a two step process. Start with 80 grit stones, (.004”
removal per minute) use ROUGH MODE and bring all cylinders to within .005” of the nal size. Switch
to stones that will leave you the desired RA value and remove the nal amount of material using FINISH
MODE.
When there is less that .010” to remove start with 270 grit stones and bring cylinders to within .002” of
nal size using ROUGH MODE. Switch to stones that will leave you the desired RA value and remove
the nal amount of material using FINISH MODE. You can also use the 270 grit stones and bring the
cylinder to nal size. Then install nishing stones and use the PLATEAU MODE 1 operation to bring the
cylinder to your desired RA value.
Common Surface Finishes
Today’s modern engines are demanding smoother and more precise surface nishes. There are two
commonly used plateau surface nishes in automotive engine cylinder bore nishing today. They are
both described below. The single step, non-plateau nish is no longer recommended for engine cylinder
bores. The processes described below are commonly used in the engine building industry. If the engine
or ring manufacturer recommends a particular nish the engine manufacturers specications or ring
manufactures recommendation should be followed.
Non-Plateau
The typical Ra nishes used for a Non-Plateau nish should be in the 16-24 range. A 16-24 Ra nish
leaves adequate peaks to be knocked off during the engine break in period yet is not so rough as to
cause oil burning problems before the cylinder walls have been plateaued by the rings. During initial start
up of the engine the rings will create the plateau by knocking off the peaks of a non-plateau nish. Most
modern ring manufacturers do not recommend using this type of nish.