Question 1

Cam Chain Tensioner Failure (3.2 Carrera)

Accepted Answer

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. The original cam chain tensioner on the 3.2 Carrera uses a ratcheting mechanism that can stick or fail mechanically. Once the tensioner loses its preload, the chain has no take-up device and immediately goes slack. The failure often occurs during cold start when oil pressure is lowest. Install the updated cam chain tensioner (the "update" or "improved" tensioner). This is a proactive replacement, do not wait for symptoms. A cold-start chain rattle is a warning that the tensioner is failing. Replacement cost: $500-$1,000 including parts and labour. The cost of ignoring it: $15,000-$25,000 for an engine rebuild.

Question 2

Valve Guide Wear

Accepted Answer

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. The valve guides are bronze alloy bushings pressed into the aluminium cylinder heads. Over 100,000+ km, the guides wear, developing clearance that allows oil to pass. The exhaust valve guides wear faster due to higher temperatures. Cylinder head removal and reconditioning, new valve guides, new valve seals, valve lapping, and head resurfacing. Cost: $3,000-$6,000 per pair of heads (the 911 has two cylinder banks, each with its own head).

Question 3

Oil Leaks, The Usual Suspects

Accepted Answer

Oil residue on every surface of the engine. Active dripping in the garage. The air-cooled flat-six has numerous gasket and seal surfaces that age and leak over decades. The engine runs hot (air-cooled, operating under the rear deck lid), and the thermal cycling accelerates gasket deterioration. 1. Valve covers: The simplest leak. Replacement gaskets and retorquing fixes it. Cost: $50-$100 DIY. 2. Oil return tubes: The tubes that return oil from the heads to the case develop leaks at their seals. Cost: $200-$400. 3. Cam chain housing cover: The large cover at the centre-rear of the engine seals with an O-ring that hardens. Requires engine removal for proper access on most models. Cost: $400-$800. 4. Cylinder base seals: The cylinders are sealed to the case with rubber O-rings. When these leak, oil runs down the outside of the cylinders. Requires pulling the cylinders, essentially a top-end rebuild. Cost: $3,000-$6,000. 5. Cam chain housing-to-case seal: The most significant leak. Requires splitting the case, effectively a full rebuild. Cost: $8,000-$15,000.

Question 4

2.7-Litre CIS Engine, Nikasil Cylinder Scoring

Accepted Answer

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

Question 5

Thermal Reactor Exhaust Damage (1975-1977)

Accepted Answer

Exhaust valve recession, burnt valves, cracked exhaust studs. The thermal reactor runs extremely hot to burn unburned hydrocarbons. The thermal reactor system was Porsche's solution to US emissions regulations before catalytic converters became standard. It operates at much higher temperatures than a conventional exhaust, stressing the exhaust valves and the cylinder head studs. Replace the thermal reactor with a conventional exhaust manifold and catalytic converter (or, for track-only cars, a header). Replace burnt valves and cracked studs. Cost: $1,500-$3,000 for exhaust conversion, $2,000-$4,000 for valve work.

Question 6

915 Gearbox, Second Gear Synchro Wear

Accepted Answer

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. The 915 gearbox's second gear synchro takes the most punishment in normal driving. The synchro ring is brass and wears against the steel gear cone. Heavy-handed shifting and infrequent oil changes accelerate the wear. Gearbox rebuild with new synchro rings. The gearbox must be removed from the car. Cost: $3,000-$6,000 at a specialist.

Question 7

915 Gearbox, Shift Linkage Slop

Accepted Answer

Vague, imprecise shifting. Difficulty finding gears, especially third and fourth. The 915's shift linkage uses multiple rod joints and bushings that wear with age. The linkage is long (gearbox at the rear, shifter in the centre console), and any play is amplified. Replace the shift coupler (the rubber bushing at the rear of the linkage), shift rod bushings, and adjust the linkage. A complete linkage rebuild transforms the shift quality. Cost: $200-$500 for parts.

Question 8

Battery Box and Kidney Area Corrosion

Accepted Answer

The front luggage compartment, particularly the passenger side where the battery sits, develops severe corrosion. The "kidney" panel, a complex curved panel between the inner wing and the front bulkhead, rots from trapped moisture. Battery acid vapour corrodes the battery box and surrounding panels. The kidney area is a double-skinned structure that traps moisture between layers. Water from blocked windscreen drains pools in this area. Cut out corroded metal and weld in repair panels. The kidney panel is complex to fabricate and requires an experienced 911 body specialist. Cost: $3,000-$8,000 depending on severity.

Question 9

Sill and Rocker Panel Corrosion

Accepted Answer

The sills (rocker panels) that run along the bottom of each door develop rust, perforation, and structural weakness. Road spray, blocked drain holes, and accumulated debris trap moisture inside the sill structure. Stone chips from the front wheels break the paint and expose bare steel. Cut out corroded sections and weld in repair panels. Full sill replacement is available from specialists. Cost: $2,000-$5,000 per side.

Question 10

Alternator and Charging Issues

Accepted Answer

Low charging voltage, flat battery, dim lights. The red generator/alternator light stays on or flickers. The alternator on air-cooled 911s is engine-mounted and runs at high temperature. The internal regulator and brushes wear, reducing output. The serpentine belt (or V-belt on older cars) that drives the alternator also drives the cooling fan, if the belt snaps, you lose both charging and engine cooling simultaneously. Alternator rebuild or replacement: $300-$600. Belt replacement: $50-$100. Always carry a spare belt, a broken belt means immediate overheating.

Question 11

CDI Ignition Module Failure (1969-1977)

Accepted Answer

Engine cuts out without warning, intermittent misfiring, no-start condition. The Capacitive Discharge Ignition module fails. The CDI module is a sealed electronic unit that degrades with age and heat. Failure is typically intermittent before becoming permanent. Replace the CDI module. Aftermarket replacements are available and more reliable than the original Bosch units. Cost: $300-$600.

Question 12

Heat Exchanger Failure

Accepted Answer

Exhaust fumes enter the cabin through the heater. Carbon monoxide poisoning risk. The 911's cabin heating works by passing fresh air through heat exchangers wrapped around the exhaust pipes. When the heat exchangers corrode and develop holes, exhaust gas mixes with the heated air. Replace the heat exchangers. Stainless steel replacements are available and significantly longer-lasting than the original mild steel units. Cost: $800-$1,500 for a pair of aftermarket heat exchangers plus installation.

Question 13

Torsion Bar Sag

Accepted Answer

The car sits lower than factory specification, particularly at the front. The ride becomes harsh and the car bottoms out over bumps. Torsion bars lose their spring rate over decades of loading. Heat, corrosion, and accumulated fatigue cycles contribute. Replace the torsion bars or have the existing bars reset by a specialist. Adjustable spring plates at the rear allow some compensation. Cost: $500-$1,500.

911 (Classic Air-Cooled)

911 (Classic Air-Cooled) known problems