I refused head service at a Subaru specialty shop because I was frustrated installing springs and retainers on valve cores on an OHV Subaru. Since the local workshops were also too busy to make this 6 cylinder, I set out to find an adapter for my C-Clamp supercharger. I found this tool and love the reviews. I had no idea! What used to take me 15-20 minutes per valve sometimes took a maximum of 30 seconds. Basically this is installing the seal, spring seat, spring retainer and installing the retainers in place. Press the conical spring-loaded anvil against the valve stem and press hard and fast or hit with a hammer - done! I was looking around the store to tell someone, but I work alone. I'm not easily impressed, but this tool did the trick! I had a piece of memory foam under the valves to hold them in place. With a flat head on a workbench, the valves were at an angle. I had to make sure the tool was at the same angle. Some reviews said it didn't work, I think it's because they didn't keep their mouths shut properly. I'm back in business.