Engine Block Honing for Plateaued Cylinder Walls

Car engines with dual overhead camshafts (DOHC) provide more power and run at higher speeds. With four valves per cylinder, DOHC engines like the ones used in some Saturn automobiles allow more air to enter and more exhaust to leave. Higher-performance engines require proper maintenance, of course, and excessive heat from a lack of coolant can damage the engine block and cause the pistons to seize.

Such was the poor condition of a 1996 DOHC block that an engine builder from SaturnFansForums.com wanted to restore. Using a rigid honing stone, TomM96 spent “the better part of a week” with four damaged engine cylinders. Out-of-round and tapered, each cylinder was a different size. Honing them to “about the right size” wasn’t working, so TomM96 sought some advice from a local machine shop.

Plateaued Cylinders: Diamond Hones and Ball Hones
The solution, the machinist explained, was to use the right tool – “a special diamond hone” from Brush Research Manufacturing (BRM). OldNuc, another expert from SaturnFansForum.com, agreed. TomM96 needed to “bore out” each cylinder with a 100-grit flexible diamond hone, and then surface finish the cylinder walls with a 280/320 ball hone. “This is the process for creating plateaued cylinders”, OldNuc explained, adding that the BRM website provides “a detailed process description of how it is done”.

Flexible Honing: From Cylinder Boring to Wall Finishing

So TomM96 began reading our Technical Books about flexible honing. The first technical document he downloaded describes common practices in cylinder boring, honing and wall finishing. Known as the Gold Booklet, this resource also compares the surfaces of cylinder walls that have been finished with rigid hones (such as honing stones) vs. the Flex-Hone® tool from Brush Research Manufacturing.  

TomM96 also downloaded A Study of Cylinder-Wall Micro-Structure and The Necessity of a Plateaued Cylinder Wall Finish. The study of cylinder wall microstructure used a scanning electron microscope (SEM) to compare cylinder honing with the Flex-Hone® vs. rigid hones. The study of plateaued cylinder walls uses several test engines to demonstrate the “lower blow-by, increased compression, less ring and cylinder wall wear with the Flex-Hone® process.”

After visiting the BRM website and examining these technical references, TomM96 returned to SaturnFanForums.com and thanked OldNuc. “I am now a Believer in Flex/Ball hones!,” he explained.