SOHC LK0/L24

The SOHC (LK0/L24) cylinder head had 8 valves and was made of lost foam cast aluminum. The camshaft was located in the center of the cylinder head and driven by a chain off the front crankshaft sprocket. Motion from the camshaft was transmitted to the eight valves by the hydraulic lifters and rocker arms.
The LK0 engine first used TBI (Throttle Body Injection) for fuel delivery and was rated at 85 hp (63 kW) at 5000 RPM and 107 lb·ft (145 N·m) at 2400 RPM from 1991 to 1994.
The L24 engine received MPFI (Multi-Port Fuel Injection) in 1995 which increased power output to 100 hp (75 kW) at 5000 RPM and 115 lb·ft (156 N·m) at 2400 RPM. In 1999, these engines switched from the recessed top pistons of the previous models to all new flat top pistons that were also used in the twin cam models. The cylinder head was also redesigned to keep the compression ratio at 8.8:1 even with the flat top pistons and now featured provisions for an air injection reaction system. This engine was used from 1995 to 2002.
The SOHC engine was available on the base model S-series vehicles (SC1, SL, SL1, SW, SW1)
1992 through 1998 L24 Cylinder heads developed issues with cracks developing in the fifth camshaft journal, located closest to #4 cylinder. The hairline crack would develop between the oil feed port of that journal and the coolant passages in the cylinder head. Symptoms would range from overheating to low coolant, however, most cars affected by this issue exhibited oil migration into the cooling system. The resulting mixture of the two fluids would result in a thick brown "milkshake"-like mixture, visible in the coolant overflow tank.
Saturn released unadvertised policy which would cover this issue, extending the warranty on the cylinder head to 6 years or 100,000 miles (160,000 km).
Repair required the replacement of the cylinder head. and flushing of the coolant system. Badly affected cars would see coolant in the oil, as well as oil in the coolant, and would require the replacement of the complete engine assembly.
Until the cylinder head casting was redesigned some time in 1998, some vehicles would require this repair more than once, and replacement cylinder heads could develop the same crack.
It was estimated that between 2% and 5% of SOHC Saturn S-Series vehicles were affected by this defect. DOHC engines had a different cylinder head, and did not suffer the same issue.

DOHC LL0

The DOHC cylinder head had 16 valves and was made of lost foam cast aluminium. The camshafts were held in the cylinder head with bearing caps and driven by a chain off the front crankshaft sprocket. Motion from the camshafts was transmitted to the 16 valves by direct-acting hydraulic lifters.
LL0 cylinder heads were changed slightly in 1995, when Saturn adopted electronic, linear EGR mechanisms, over the previous vacuum actuated design. The head casting was changed to accommodate different mounting surface of the new valve.
All LL0 engines used MPFI and were rated at 124 hp (92 kW) at 5600 RPM and 122 lb·ft (165 N·m) at 4800 RPM. The DOHC engine was available on the upper-level model S-series vehicles (SC, SC2, SL2, SW2). A revision of the LL0 appeared in 1999 and used a roller camshaft with hydraulic lifters and rocker arms, but power was unchanged. Also for 1999 provisions for a new air injection reaction system was introduced aimed at improving engine emissions.