911 (Classic Air-Cooled)

1964-1989 / Coupe / Targa / Cabriolet / Germany

All 911 (Classic Air-Cooled) problems All workshop issues

Critical Engine

2.7-Litre CIS Engine, Nikasil Cylinder Scoring

Symptoms

Increased oil consumption, loss of compression, rough running, and blue exhaust smoke. The engine gradually loses power and efficiency.

Cause

The 1974-1977 2.7-litre CIS engine used Nikasil-coated aluminium cylinders instead of the traditional cast-iron cylinders used in earlier and later engines. The Nikasil coating is a nickel-silicon carbide plating that provides a hard, low-friction bore surface. However, thermal distortion causes the aluminium cylinder to flex, cracking the Nikasil coating. Once cracked, the coating flakes away, and the bore loses its seal with the piston rings.

Fix

Replace the Nikasil cylinders with aftermarket slip-in steel liners or Mahle/Cima cast-iron cylinders and pistons.

This requires a top-end teardown but not a full engine split.

Cost: $5,000-$8,000.

Cost mentioned in fix

Cost: $5,000-$8,000

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Other known issues

Minor Engine

Cam Chain Tensioner Failure (3.2 Carrera)

The cam chain tensioner fails, allowing the duplex timing chain to go slack. The chain skips teeth on the sprockets, the camshaft timing shifts, and the valves collide with the pistons. The result is catastrophic, bent valves, damaged pistons, and potentially a cracked cylinder head.

Common Engine

Valve Guide Wear

Blue smoke from the exhaust on start-up (oil pooled on valve heads drains into the combustion chamber) and on the overrun (oil drawn past the guides by manifold vacuum). Increased oil consumption.

Critical Engine

Oil Leaks, The Usual Suspects

Oil residue on every surface of the engine. Active dripping in the garage.

Common Engine

Thermal Reactor Exhaust Damage (1975-1977)

Exhaust valve recession, burnt valves, cracked exhaust studs. The thermal reactor runs extremely hot to burn unburned hydrocarbons.

Common Transmission

915 Gearbox, Second Gear Synchro Wear

Second gear crunches or grinds on downshifts, especially when cold. The synchro cannot match shaft speeds before gear engagement. Over time, it worsens and eventually grinds on upshifts as well.

Common Transmission

915 Gearbox, Shift Linkage Slop

Vague, imprecise shifting. Difficulty finding gears, especially third and fourth.

View all 13 911 (Classic Air-Cooled) problems