START YOUR ENGINES! Machining Top Notch Dirt Bike Parts!

How do you machine a custom power valve cover for a legendary Honda CR125 dirt bike engine? In this video, Jonathan from 2SM Performance takes you behind the scenes of his latest project—building a custom part for a customer restoring factory team engines from the early 2000s. This isn’t just any part. The customer requested an extended feature to fit a stroker crankshaft, and the part had to be machined from Zinc 68 magnesium, a tricky and flammable material. Jonathan shares his full process, from programming toolpaths in CAM software to machining a test piece in aluminum before committing to magnesium. Along the way, he explains his decisions, including how he: Set up the stock to maximize rigidity and accuracy Used 2D and 3D adaptive milling for efficient roughing Programmed finishing passes to achieve smooth contours and tight tolerances Adjusted tools and strategies to handle challenges like chatter and chamfer issues You’ll also see how Jonathan problem-solved on the fly, refined his workflows, and ensured the part was perfect before final production.