Our warranty, in the event that you have an issue. This helps us catch any issues before they make it to the customer. And are continuing to build towards 100% testing. We run 9 out of 10 engines that leave our facility. Because of the vast inventory of used parts from our salvage operation we have been able to build test cradles or test rollers. The final step in the process here at PSN is to test run your engine. All bolts are torqued to appropriate specs for each engine type. Each engine is hand built with quality workmanship to insure the longevity of your powerplant. Assembly begins after all parts are inspected and the replacement parts are on hand. If they don't appear to be near new, they will be rebuilt or replaced. Oil pumps are a crucial component in the build. Any other worn internals will be replaced where needed. All bearings, shift forks and gears are replaced where needed. All parts are visibly inspected or measured for wear. Crankshaft roller bearings are replaced where needed. If automotive style crank and rods are used in the application, all bearings are replaced. If they are not in excellent or near new condition, they are rebuilt or replaced. Cylinders are always overbored to the next size or sent off and replated. All valves, guides and seats are checked and replaced if needed. All heads are checked for trueness and surfaced or planed if necessary. Heads are refreshed or rebuilt (on a Rottler Head Machine SG7MTS) with the valves adjusted. All rebuilt engines include new piston(s) and rings, new gaskets and seals, new timing chain (where applicable), water pump seal kit (if water pump is part of assembly), new oil filter, and new spark plug(s). We offer a $100-$200 core refund when you return your used engine to us (free of charge!)- return instructions included in the packaging. Freshly rebuilt Kawasaki Mule 3000/3010/3020 KAF620 powerplant- fits all years.