2006 subaru legacy gt
DOHC EJ25 Subaru engines sometimes burn valves, typically exhaust valves. This happens because the back sides of the valves wear against the valve seats making the valves concave shaped where they sit on the seats. This means the valves go deeper into the seats which ends up tightening up the valve tip-to-bucket clearances. If that valve bucket clearance gets too tight, the valves will actually hang open just enough for the hellfire inside the combustion chamber to go around the edge of the valve with it closed and burn (melt) it. As soon as the valve burns, the compression in that cylinder is permanently lost, and the engine begins running terribly. The only fix is to remove and rebuild the cylinder heads, and reinstall them on the engine, which typically means new head gaskets, head bolts, timing belt, water pump, cam seals, and a variety of other logical small items.
Unfortunately the DOHC engines have non-adjustable valve lash. Their valve spacing is based on the solid valve buckets. Valve buckets come in a variety of sizes. So if the valve clearance on your intake valves is not near .20mm and if your exhaust valve bucket clearances are not near .35mm, you'll need to replace the valve buckets with ones with the proper clearance.
