When an engine is rebuilt, the cylinders usually need attention. Wear tends to create taper in the upper part of the cylinder that can reduce ring sealing and increase blowby and oil consumption if not removed. The cylinder may also be out of round, scored or have other damage that requires correcting before a new set of rings will seal properly.

The main objective when refinishing the cylinders is to:

• Make the walls as parallel as possible (no taper).
• Make the bores as round as possible.
• Have the right amount of crosshatch for good oil retention and ring support.
• Produce a surface finish that meets the requirements of the rings.

This is achieverd by boring and/or honing the cylinders in one or several steps with various types of abrasives.After honing, the cylinders are cleaned to remove residual abrasive and metallic debris that’s left in the bores. The best way to get rid of this material and smooth the bores is to “polish” the bores after honing with a flexible abrasive brush.Brushing after honing not only helps clean the bores, but also plateaus the surface. Brushing sweeps away the torn and folded metal as well as the sharp, jagged peaks leaving a much smoother surface.One of the advantages of a plateau bore finish is that it preconditions or breaks-in the cylinders. This reduces the time it takes to seat a new set of rings as well as initial ring wear, blowby and oil consumption. The engine delivers good compression right away, there’s no blue smoke in the exhaust, emissions and oil consumption are reduced and the rings last longer because they haven’t had to wear to conform to the bores.

A plateau bore surface also provides increased bearing area to support the rings while retaining enough depth in the crosshatch for good oil retention and lubrication. That’s why the original equipment engine manufacturers (OEMs) favour this type of bore finish and use it in most new engines.

Here at ASD Engines Ltd. we use a modern Rottler HP6A Honing Machine.We can achieve all the tolerances required by OEMs and Piston Ring manufacturers to ensure that our customers can be confident that our engine machining is second to none.For a more in depth look at Cylinder Bore Honing take a look at this article.