Inlet Valve Guide 1st Oversize. Porsche 993 1994-98  ›  99310432271

Inlet Valve Guide 1st Oversize.

The TRW 1st Oversize Inlet Valve Guide is a precision replacement component for the cylinder head of Porsche 911 (993) models. The valve guide supports and accurately locates the inlet valve stem as the valve repeatedly opens and closes, keeping the valve correctly aligned with its seat.
x6 Per Engine.
Price Is For Each.

Fits:

• Porsche 993 1994-98

Diagram Ref No 3

Correct valve guidance is essential for smooth valve operation, effective combustion-chamber sealing and long-term cylinder-head reliability. The first-oversize specification is intended primarily for cylinder-head rebuilding or refurbishment where the original valve-guide bore has worn or been machined and a standard-size guide no longer provides the required interference fit.

What This Product Does:

• Supports and accurately guides the inlet valve stem.
• Prevents excessive sideways movement or valve wobble.
• Keeps the valve correctly aligned with the valve seat.
• Promotes consistent valve seating and combustion-chamber sealing.
• Helps protect the valve stem, valve seat and cylinder head from accelerated wear.
• Provides an oversize external fit for cylinder heads requiring a first-oversize valve guide during refurbishment.
• Helps restore correct valvetrain operation during a professional cylinder-head rebuild.

Symptoms Of Wear Or Failure:
Worn valve guides can allow excessive movement between the valve stem and guide. Possible symptoms include:

• Increased engine oil consumption.
• Blue exhaust smoke, particularly after start-up or during deceleration.
• Excessive valve-stem movement or valve wobble.
• Ticking or increased valvetrain noise.
• Poor or inconsistent valve seating.
• Reduced compression in an affected cylinder.
• Rough idle, misfires or reduced engine performance.
• Oil-fouled spark plugs.
• Accelerated valve-stem or valve-seat wear.
• Excessive valve-guide clearance discovered during cylinder-head inspection or rebuilding.

As guide wear increases, the valve may no longer locate accurately against its seat, potentially reducing combustion efficiency and contributing to further valve and cylinder-head wear.

Why Replacement Matters:

• Valve guides operate under constant heat, friction and rapid reciprocating movement. Once clearance becomes excessive, the valve can move laterally rather than travelling accurately along its intended axis. This can compromise valve seating, increase oil consumption and place additional stress on the valve stem and seat.
• Leaving badly worn guides in service can contribute to damaged valve seats, worn valve stems, poor sealing and potentially more extensive cylinder-head repairs. Installing the correct replacement guide restores controlled valve movement and helps maintain reliable compression, efficient combustion and long-term engine durability.
• The 1st oversize version is particularly important during cylinder-head refurbishment where the guide mounting bore can no longer securely retain a standard-size guide. Correct sizing and professional machining allow the replacement guide to achieve the required fit within the cylinder head.

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

99310432271

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