Original Porsche Part Genuine Porsche part 99310432170

Exhaust valve guide 1st oversize.
This set of 6 intake valve guides (1st oversize) is designed for professional cylinder-head rebuilds on Porsche 993 air-cooled flat-six engines. Manufactured to match original Porsche dimensions, material specifications, and hardness ratings, these guides ensure the intake valves operate with correct alignment, stability, and sealing performance - all essential for maintaining proper combustion and long-term engine reliability.
SET OF 6

Fits:
Porsche 993 1994 - 1998

Diagram Ref no 3.

• Use Cases: Head rebuilds; valve-seat re-cut; restoring compressed guide bores; upgrading worn or damaged valve guides; preventive maintenance where valve guide integrity is uncertain.

Oversize valve guides are used when the cylinder-head guide bores have worn or been machined during refurbishment. This set provides a complete, matched group of intake guides, ensuring uniform fitment and valve control across all cylinders. With precision-machined tolerances and excellent heat resistance, these OE-match guides restore the valve train to factory behaviour, eliminating excessive valve play and preventing compression loss, misfires or premature wear.

Perfect for engine rebuilders, restorers, and anyone refreshing a 993 cylinder head, this set supports smooth, accurate valve movement and optimal sealing under the high temperatures and RPM conditions typical of Porsche’s air-cooled performance engines.

Valve guides endure constant thermal cycles, valve-spring force, and high-speed motion. Over time they can wear, enlarge, or become loose - causing:
• Valve wobble and mis-alignment
• Poor sealing at valve seats - resulting in compression loss, misfires, or exhaust leakage
• Increased valve-stem wear, potential seat damage, or premature engine wear
• Reduced engine efficiency, elevated emissions, and unsafe reliability.

Replacing worn or oversized guides with a proper unit restores correct valve operation, extends cylinder-head life, ensures compression integrity, and brings the engine back to spec - critical for performance, reliability, and longevity.



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Related, superseded, cross reference or alternative numbers for comparison.

99310432271

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Exhaust valve guide - 1st oversize - set.
This is a set of six OE Match quality exhaust valve guides designed for the air-cooled Porsche 911 (993) engines produced between 1994 and 1998. These are 1st oversize valve guides, meaning they are slightly larger than standard guides to accommodate engines that have been reamed or show wear in the original guide bores. The set contains six guides, enough for a full cylinder head rebuild on the exhaust side.
SET OF 6

Fits:
Porsche 993 1994 - 1998

Diagram Ref no 2.

Valve guides are precision metal bushings pressed into the cylinder head that support and guide the movement of the exhaust valve stems. Over time, original guides can wear, allowing excessive valve stem play, reducing seal effectiveness, and increasing engine oil consumption. These OE Match valve guides are manufactured to match Porsche’s original specifications, including diameter, material quality and machining tolerance, but in a 1st oversize dimension so they fit reamed cylinder heads.

This SET OF 6 provides a complete set for one engine’s exhaust side - ideal for cylinder-head rebuilds, valve jobs or whenever the exhaust guide bores are undersized due to wear.

The exhaust valve guides:
•  Support and align the exhaust valve stems so they travel accurately within the head.
•  Maintain correct valve seating and combustion sealing, which is vital for performance and compression.
•  Help conduct and dissipate heat from valves into the cylinder head casting.
•  Reduce lateral valve stem movement, decreasing wear on stems and valve seats.

By replacing old or worn guides with a matched oversize set, you can restore tight tolerances in the valve train and help ensure efficient combustion and long-term reliability.

Valve guides wear over time due to heat, friction, and repeated valve movement. When guides become worn or oversized gaps develop between the valve stem and guide bore, the following issues can arise:
•  Loss of performance and power
•  Higher oil consumption
•  Reduced sealing and compression
•  Increased valve train wear

Installing a correct OE Match valve guide restores correct valve alignment, reduces unwanted movement, supports proper seat sealing, and prolongs the life of your engine’s top end - especially in rebuild or high-mileage applications.

Replace valve guides if you observe:
•  Blue smoke from the exhaust (signifying oil burning)
•  Rough idle or hesitation
•  Poor compression or loss of engine power
•  Valve stem play when checked during teardown
•  During a cylinder head rebuild or valve job

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

99310432172

The product you are viewing cross references to these numbers