Edge Chamfering and Cylinder Porting for Two-Stroke Engines

Edge chamfering is a surface finishing technique that smoothes the edges of cylinder ports so that piston rings seat properly. Cylinder porting, a related technique, is designed to improve flow characteristics and promote optimum engine performance. For the two-stroke engines used in scooters, motorcycles, and mopeds, edge chamfering and port work are important cylinder restoration tasks. Opening the port and aligning the holes are critical, but so are achieving proper port timing and accurate port shape. If an engine builder removes too much material with a file and sandpaper, the cylinder port may be ruined.

Surface Finishing, Not Material Removal
That’s why experienced bike mechanics choose the Flex-Hone® tool from Brush Research Manufacturing (BRM). The Flex-Hone® is a surface finishing tool, not a material removal tool. By reducing the rough, uneven peaks of a metal surface’s microstructure, this flexible hone removes only the right amount of material. Unlike other honing tools, the Flex-Hone® also produces an unmatched controlled surface condition. With their soft cutting action, the tool’s abrasive globules have an independent suspension that makes the Flex-Hone® self-centering, self-aligning to the bore, and self-centering for wear.  

Brush Tools and Cylinder Restoration
For the scooter mechanics at 49ccScoot.Com Forums, a user named 90GTVert offered a valuable lesson in using brush tools for edge chamfering and cylinder porting. After using metal-bristled brushes to clean the cylinder head on his favorite motorbike, 90GTVert began restoring the cylinder itself. Although the “scuffing” was minor, there was still “a lot of carbon” to be removed. Next, 90GTVert raised the exhaust port opening by 1 to 1.5mm. Opening this outlet improved the connection to the exhaust pipe, but also required “smoothing the port a bit”.

The Flex-Hone® for Port Chamfering and Plateau Finishing
After chamfering the port edges, 90GTVert prepared to use his “handy dandy 54mm ball hone”. Although some users call BRM’s trademarked tool a ball hone, you know you’ve got the best if it says Flex-Hone®. The BRM brush tool “did a great job of chamfering the ports even smoother,” the scooter enthusiast explained, “and it knocked out the ridge at the top of the cylinder”, he added. “Just 30 seconds with a ball hone does wonders,” he advised the other members of 49ccScoot.Com Forums. As the picture that accompanies this blog entry shows, the Flex-Hone® tool also produces a cross-hatch pattern for a plateau finish and optimum lubrication.