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What is Porsche bore scoring?

What is Porsche bore scoring?

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Enric Godes

Bore scoring affects the M97 engines of the 997.1 versions, the GTs aside. It happens when the cylinders wear unevenly, leaving scores and scratches on the cylinder walls.

Porsche bore scoring

Bore scoring is a problem that, from 1997 to 2008, affects every Boxster, Cayman and 911 with the M96 and M97 engines.

The main cause is the coating coming away from the pistons.

At Valentin Motors we sleeve the block with the one definitive solution to this problem: NSC.

NSC is an alloy of nickel, silicon and carbide, very close to NIKASIL (used on the air-cooled cars and the GTs), and it is the only definitive answer.

Causes of bore scoring

Because of the dry-sump layout on the 996 and 997, the oil cooling system and the cooling flow face the underside of the cylinders. That means the thrust of the piston in the right-hand bank runs slightly hotter than on the left. The result is that the sixth cylinder takes more punishment than it should once thermal and mechanical loads are applied.

When the iron coating comes away from the piston skirt, the cylinder seizes.

Cylinder lubrication can also be compromised if the oil is only changed every two years. When fuel and moisture contaminate the oil, from short low-mileage trips, the oil thins out. That generates friction between piston and cylinder wall and can lead to overheating.

Symptoms of bore scoring

  • Loss of engine power.
  • Abnormal engine noise: a piston knocking.
  • Higher fuel consumption.
  • Excessive oil consumption.
  • More smoke from the exhaust.

Porsche models affected by bore scoring

Every Boxster and Cayman from 1997 to 2008, and the 911 with M96 and M97 engines.

Below, an example of an M97 block sleeved with Nickies (NIKASIL), ready for assembly.

In this case the displacement was also taken from 3.8 to 4.0.

Sleeved cylinder bores of an M97 engine block, with the honing crosshatch visible
Three cylinder bores of an M97 block seen from the cylinder head face
Close-up of a finished sleeved bore, beside the block's threaded hole

Preventing bore scoring

  • A sound service history.
  • A cooling system in good order, to reduce the chance of a localised hot spot in a cylinder.
  • Not using the car exclusively for short trips, with the engine running rich.
  • Checking the injectors and the MAF.
  • Changing the oil regularly, every 12 months.

The solution to bore scoring on a Porsche

The only definitive solution is sleeving all six cylinders in NSC, Nickies.

Note: sleeving one or several cylinders in iron or steel is not the solution. These blocks were not designed for steel liners, and the manufacturer never supplied oversize pistons for sleeved blocks.

If you would like more information, get in touch.

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