Valve Cotter Half. Porsche 356 / 911 / 964 / 924S / 944 / 928  ›  90110541700

Valve Cotter Half.

The TRW Valve Cotter Half is a replacement valve-spring retaining collet for selected classic Porsche engines.
Sold Each.
x2 Required Per Engine Valve.

Fits:

• Porsche 356C / SC - 1963 to 1965
• Porsche 911 - 1965 to 1989
• Porsche 964 - 1989 to 1994
• Porsche 944 - 1982 to 1991
• Porsche 928 - 1978 to 1986

Diagram Ref No 16

Also known as a valve keeper, valve collet or valve lock, this small but critical component fits into the machined groove near the top of the valve stem and locks into the valve spring retainer.

Each valve requires two cotter halves. When installed together, the two halves form a tapered locking arrangement that secures the valve spring and spring retainer to the valve stem.

What This Product Does:
The valve cotter forms part of the cylinder-head valvetrain.

Its job is to mechanically lock the valve spring retainer to the valve stem.

The assembly typically consists of:

• Engine valve
• Valve spring
• Spring retainer
• Two valve cotter halves

When the valve spring is compressed during assembly, the two cotter halves are installed around the valve-stem groove.

As the spring compressor is released, the spring retainer presses against the tapered outside surface of the cotters and locks them securely into position.

This allows the spring to remain attached to the valve while the engine operates at high speed.

Symptoms Of Wear Or Failure:
Valve cotters usually do not produce gradual external symptoms in the same way as a bearing or seal.

Problems are most commonly discovered during cylinder-head inspection or after another valvetrain fault develops.

Possible warning signs include:

• Unusual valvetrain ticking
• Metallic noise from the cylinder head
• Valve spring retainer sitting incorrectly
• Visible cotter movement
• Uneven cotter seating
• Damaged valve-stem groove
• Cracked or chipped cotter
• Wear marks around the locking surfaces
• Spring retainer sitting at an abnormal angle
• Valve clearance changing unexpectedly
• Misfire following valvetrain damage
• Loss of compression
• Serious mechanical noise after a cotter releases

A correctly installed cotter should remain securely locked and should not visibly move relative to the spring retainer.

Why Replacement Matters:
A damaged valve cotter should never be ignored.

If the cotter loses its grip on the valve stem, the spring retainer can release.

This can allow the valve to drop into the cylinder.

Potential consequences include:

• Valve-to-piston contact
• Bent valve
• Damaged piston
• Broken valve guide
• Cylinder-head damage
• Combustion-chamber damage
• Severe engine failure

Because the possible consequences are so serious, questionable cotters should be replaced during cylinder-head service rather than reused.

Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.

90110541700

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