Exhaust Valve Guide 1st Oversize. Porsche 993 1994-97  ›  99310432172

Exhaust Valve Guide 1st Oversize.

The TRW 1st Oversize Exhaust Valve Guide is a precision replacement component designed for the cylinder head of Porsche 911 (993) models. The guide supports the exhaust valve stem and keeps the valve accurately aligned as it opens and closes, helping the valve seat correctly and maintain an effective combustion-chamber seal.
x6 Per Engine.
Price Is For Each.

Fits:

• Porsche 993 (911) C2 1994-97
• Porsche 993 (911) C4 1994-97
• Porsche 993 (911) RS 1994-97
• Porsche 993 (911) C2S 1994-97
• Porsche 993 (911) C4S 1994-97  

Diagram Ref No 2

This 1st oversize version is intended for cylinder-head rebuilding where the original valve-guide bore has become worn or has been machined and a standard-size guide can no longer achieve the correct interference fit. Reference specifications list the guide as 8 x 13.26 mm. It is supplied individually, with six exhaust guides required for a complete engine.

What This Product Does:

• Supports and accurately guides the exhaust valve stem.
• Keeps the valve correctly aligned with its valve seat.
• Reduces excessive sideways movement and valve-stem wobble.
• Helps maintain effective cylinder sealing and compression.
• Assists with transferring heat from the exhaust valve stem into the cylinder head.
• Reduces abnormal loading and wear on the valve stem and valve seat.
• Provides an oversize external fit for cylinder heads requiring a 1st oversize guide.
• Helps restore correct valvetrain operation during a cylinder-head rebuild.

Correct valve guidance is particularly important on the exhaust side because exhaust valves and guides operate under very high thermal loads. Excessive clearance can prevent the valve from locating consistently against its seat and accelerate wear elsewhere in the cylinder head.

Symptoms Of Wear Or Failure:
A worn exhaust valve guide may cause:

• Blue or blue-grey exhaust smoke caused by oil entering the combustion chamber.
• Increased engine oil consumption.
• Excessive valve-stem play when inspected.
• Ticking or tapping noises from the cylinder head.
• Rough or uneven idle.
• Reduced engine performance or power.
• Poor or inconsistent compression.
• Engine misfires.
• Poor valve seating.
• Accelerated exhaust valve or valve-seat wear.
• Failed compression or leak-down test results.

As valve guides wear, their ability to accurately locate the valve against its seat decreases, which can compromise sealing and engine performance.

Why Replacement Matters:

• Exhaust valve guides are continually exposed to heat, friction and rapid valve movement. Over time, wear can increase the clearance between the valve stem and guide, allowing the valve to move laterally rather than travelling accurately along its intended path.
• Excessive valve movement can lead to poor valve seating, reduced compression, increased oil consumption and accelerated wear of the valve stem and valve seat. If left unresolved, the resulting wear can contribute to more extensive and expensive cylinder-head damage.
• Replacing worn guides restores controlled valve movement, supports consistent valve seating and helps protect the valve, valve seat and cylinder head. A correctly fitted guide also contributes to reliable compression, efficient exhaust-gas flow and long-term engine durability.
• The 1st oversize specification is especially important during cylinder-head refurbishment where the original guide bore has worn or been machined beyond standard dimensions. Using the correctly sized oversize guide allows the required secure fit to be restored.

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

99310432172

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