Valve Guides are a wear-item. They wear over time and eventually should be replaced. The higher you rev, and the harder you push your engine, the more important tolerances become. If you are spending the time and money to upgrade your valvetrain, be sure your tolerances are correct by replacing your high mileage guides with brand new aftermarket valve guides. BC premium valves guides are made from Manganese Silicon Aluminum Bronze alloy and CNC machined to exacting tolerances. BC guides are resistant to cracking and corrosion, while reducing friction and insures high lubrication even at elevated engine temperatures and rpm's. The perfect replacement to worn or damaged guides and 100% compatible with BC's lineup of stainless steel valves.