Original Porsche Part Genuine Porsche part 99903108450

Code: 99903108450

Genuine Porsche part

Original Porsche Part

The product code 99903108450 was also found on these diagrams

810-00 - rubber washer

decorative fittings 911 upto 1968

Additional information:

• This part is brand new and unused.
• Please verify that it is 100% suitable for your specific vehicle before purchase to ensure compatibility.

Before purchasing thoroughly check part to confirm compatibility.

Related products

Head nut washer. Porsche 911 1978-89

99903109101/1

Product Information

Cylinder head nut washer (Head nut washer)
This washer is used under the cylinder head nuts on Porsche 911 engines (1978–1989). It’s a precision washer made to the same style and dimensions as the original, helping the head nut seat correctly against the engine hardware.
Price is for each, 24 required per engine.

Fits:
Porsche 911 1978 - 1989

Diagram ref no 16

The washer spreads the clamping load from the head nut, helping maintain consistent torque retention and protecting mating surfaces from damage caused by concentrated pressure.

• It’s supplied per washer (price is for each) and 24 washers are required per engine.

It provides a stable, even load surface beneath each head nut, supporting correct tightening and helping the cylinder head fastening system maintain consistent clamp force over time - especially important on engines that see repeated thermal expansion and contraction.

• Distributes head nut load to reduce point-stress on components
• Helps maintain more consistent clamping force as the engine heat-cycles
• Supports proper seating of the head nut for reliable assembly during rebuilds

Old washers can become corroded, deformed, or marked from previous torque cycles. Reusing tired hardware can affect how evenly the head nuts clamp, which can compromise long-term sealing and reliability. Fresh washers help restore proper seating and load distribution during rebuild work.

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Related, superseded, cross reference or alternative numbers for comparison.

99903109101

99903109101

The product you are viewing cross references to these numbers

Cylinder head nut & washer kit. Porsche 911 1978-89

99903109101K/KIT

Product Information

Cylinder head nut & washer kit.
A complete fastening set of 24 cylinder head nuts and 24 head nut washers used to clamp the cylinder heads and cylinder barrels to the crankcase on classic air-cooled Porsche engines. This kit contains head nuts and "Large style washers"; used for 3.0 SC, 3.2 & 3.3 Turbo engines
Includes:
24 x 90110438204/1 - OE Match Cylinder head nuts
24 x 99903109101/1 - OE Match Head nut washers

Fits:
Porsche 911 1978 - 1989

Diagram ref no 16 and 17

This OE Match kit combines the correct-style M10 cylinder head nuts (OE ref no 90110438202) with the corresponding large head nut washers (OE ref no 99903109101). Together, they provide the correct bearing surface and clamping load distribution required during engine assembly or top-end rebuilds, helping maintain sealing integrity under heat cycling and high operating loads.

Head nuts and washers can suffer from corrosion, rounding, surface wear, and reduced load consistency after multiple rebuilds. Replacing them with OE-match hardware supports accurate torque application and helps maintain long-term clamp load stability - critical for top-end durability.

When to replace:
• During any top-end rebuild or head/cylinder removal
• Nuts show corrosion, damaged hex, or thread wear
• Washers are grooved, distorted, or heat-marked
• You suspect prior incorrect torqueing or hardware reuse history
• Preventive replacement on engines with unknown rebuild history

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

99903109101K

99903109101

90110438202

99903109101

90110438203

The product you are viewing cross references to these numbers

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Original Porsche Part Genuine Porsche part 99903108450