Chevrolet Quad 4 (LD2 / LD9)

GM's first twin-cam four — the 2.3 Quad 4 and the 2.4 Twin Cam that replaced it — in the Grand Am, Grand Prix, Sunfire, Cavalier, Skylark and Malibu.

It was aggressive for its day and rough with it, which is the whole story of the two versions: the 2.3 has no balance shafts and vibrates, and the 2.4 Twin Cam added them along with a general softening. A complaint of harshness on a 2.3 is very likely the engine behaving as designed, and no amount of mount replacement changes it.

Its defining failure is the head gasket, and the reputation is earned rather than folklore. Overheating and coolant loss on one of these points there first, and a car with a history of running hot should be assumed to have consumed one. Check for coolant in the oil and exhaust before spending money anywhere else.

The 2.4 Twin Cam is the more durable of the two and shares the family's other item, the timing chain and its guides, which rattle at mileage. Both are interference designs, so a chain that jumps bends valves.