Cylinder Honing and Engine Block Rebuilds

Speed-O-Motive of West Covina, California is machine shop for hot rodders that cleans engine blocks, bores cylinders, and rebuilds engines. As guest contributor Tom Dufur of Hot Rod Engine Tech explains, the machinists and engine mechanics at Speed-O-Motive “do this on a daily basis, and after 40+ years in the trade, have got the procedure down pretty well.”

Engine Rebuilds and Tool Selection

After cleaning and bead blasting the engine block, Speed-O-Motive checks for cracks and then taps the main cap bolt holes. Instead of using a long plug tap, the experienced staff chooses a bottoming tap to avoid damaging the threads. As Tom Dufur explains, “numerous engine blocks have been ruined” by do-it-yourselfers who chose the wrong tool.

When it’s time to hone cylinder bores, the engine restoration specialists at Speed-O-Motive also choose the right tool – the Flex-Hone® from Brush Research Manufacturing (BRM). Built with a stiff metal stem and flexible nylon abrasive filaments, the BRM ball hone imparts an ideal surface finish to cylinder walls, promoting optimum lubrication and reducing engine wear.

Engine Hones and Cylinder Walls

Unlike traditional honing stones, the Flex-Hone® uses a low-temperature surface finishing technique that removes harsh peaks and creates oil-retaining valleys. This substantially flat surface or plateau surface creates a greater bearing area and promotes lubrication in engine components. Self-centering and self-aligning to the bore, BRM’s cylinder hone also aids with piston ring seating and sealing.

As Flex-Hone® users know, BRM’s plateau hone is a low revolutions-per-minute (RPM) tool with a recommended range of 500 to 1200 RPMs. Always use a lubricant, preferably Flex-Hone® oil, and never hone for longer than 20 to 45 seconds per cylinder. Choose a BRM engine hone that’s oversized for the cylinder you’ll be working with, rotate the tool prior to entry, and hone for 60 to 120 strokes per minute.   

Expert Advice for Engine Builders

As BRM explains in its easy-to-read Flex-Hone® instructions, engine builders should accelerate final stroking to produce an ideal 45° cross-hatch angle. After plateau honing is complete, it’s time to clean the engine block. Thoroughly wash each cylinder with a soft nylon brush, warm or hot water, and a mild detergent. Finally, oil the engine cylinders to prevent corrosion.  

Speed-O-Motive of West Covina, California has over 40 years’ experience, but amateur engine builders can master do-it-yourself cylinder honing, too.  Start by choosing the right tool for the job, the Flex-Hone® from Brush Research Manufacturing (BRM). Visit the BRM website for more information, where you’ll also find free technical books such as the Flex-Hone® Resource Guide.