Sometimes, efforts to uphold automotive heritage drive bold innovations. Consider the 1997-2005 Porsche 911 of the 996 generation. To safeguard its legendary status against strict safety and emissions rules, Porsche revamped nearly every aspect. Key among these was the shift from air-cooled to water-cooled M96 engines, yet the cars retained their signature 911 look and dynamic performance. Still, certain issues arose.

The standout concern involves a notorious flaw in the M96 engine: intermediate shaft (IMS) bearing failure. This defect struck enough 986 Boxsters and 996 911s to spark a class-action lawsuit, which Porsche ultimately settled. Enthusiasts may already be familiar, but for newcomers eyeing a pre-owned 996, inspecting for IMS repairs is crucial. Failures often strike without clear signs, save for tiny metal particles in the oil filter or a rear main seal leak - symptoms that might stem from unrelated troubles.

Designed as non-serviceable, the bearing lacks a scheduled maintenance window. Impeccable high-mileage examples surpassing 100,000 miles exist without IMS work, while some low-mileage cars under 25,000 miles have required it. Fortunately, reliable aftermarket IMS solutions abound, alongside 996 variants spared from the problem.

What Purpose Does the Intermediate Shaft Serve?

The rear-mounted flat-six engine in a Porsche 911 boasts horizontally opposed cylinders - three per bank - aligned east-west. Separate timing chains operate at each end of the engine. Porsche employs an intermediate shaft, equipped with end sprockets and oriented north-south along the engine's center, to align them. It links the crankshaft to the camshafts indirectly.

This setup had served Porsche reliably for years. Notably, 996 Turbo, GT2, and GT3 models retained the IMS from the prior 964 generation's battle-tested Mezger engine. There, a large plain bearing, lubricated by pressurized oil, ensures smooth, dependable operation. In contrast, standard M96-equipped 996s use a sealed, grease-packed bearing at the flywheel end. Seal breach allows bearings to scatter inside the engine like errant projectiles, risking devastating five-figure damage.

From 2001-2005, M96 engines in 996s and 986 Boxsters/Caymans used two single-row bearing types with about a 10 percent failure rate, per the 2013 lawsuit affecting nearly 58,000 vehicles. Earlier 1997-1999 units had dual-row bearings, sturdier yet not failure-proof.

The Fix, the Fuss, and Warning Signs

Opt for a 996 Turbo to sidestep this entirely - often hailed as the ultimate iteration. For others, scour service records for IMS bearing service or replacement proof, including engine swaps. The procedure typically costs $3,500-$4,000 with labor and coincides with clutch work to cut expenses, as transmission removal is required anyway.

In 2017, Porsche introduced its own IMS upgrade, while firms like LN Engineering provide advanced options. These include ceramic-bearing cartridges for replacement every six years or 75,000 miles, or durable oil-fed plain-bearing designs for life. LN tracks serial numbers for authenticity, as inspection demands disassembly.

Statistics suggest many of the 179,163 M96 996s may evade failure. Select late-2005 models feature improved non-serviceable bearings, and some enthusiasts deem the concern exaggerated. Yet Porsche's lawsuit settlement validates the risk. At four grand, prevention beats a $15,000 engine rebuild plus labor - preserving the joy of an affordable used 996.