So you’re buying a used sport quad, and the seller doesn’t know much about the engine. Is it stock? Oversized displacement? Has it been ported? Does it have a high-compression piston? He shrugs. That’s a red flag, so make sure your purchase includes a valid title. But that’s a whole different topic.

If the engine has been modified, the builder typically engraves his initials or company name somewhere visible on the cylinder. This at least gives you someplace to turn should you need more information. However, when you replace the rings, piston, or both, you might have additional information that will tell the builder exactly what you have. With the cylinder removed, you should be able to figure out piston size but inspect the jug closely for engraved notes about the build.

Duncan Racing does this with all of their builds. You’ll find their signature brand, “Paul Turner Racing,” engraved on the side of the cylinder, but if you look closer, you’ll find more specs about the cylinder. We found this old 250R Duncan-built cylinder at ATC Addiction in Arizona. When turned over, we spotted additional details engraved on the bottom side of the intake. This particular cylinder has baseplate sizing and “Special Piston” information listed. With that, one call to Duncan Racing should reveal everything we need to know about the work put in to this top end.