Cylinder Shim Set, Fits, 90.5 & 92mm, .040 In Thick, 4 Pc

Precision Deck Height Control for High-Performance Air-Cooled Engines

When you are building a high-performance Volkswagen engine, precision is the difference between a motor that screams down the track and one that suffers from premature detonation or catastrophic failure. This EMPI Cylinder Shim Set is specifically engineered for builders running 90.5mm or 92mm big-bore cylinders who need to dial in their deck height with absolute accuracy. In the world of air-cooled VWs, "deck height"the distance from the top of the piston at Top Dead Center (TDC) to the top edge of the cylinderis the most critical variable in determining your compression ratio and ensuring proper flame propagation. These .040-inch thick shims provide a reliable, mechanical solution to increase that clearance, allowing you to compensate for stroker crankshafts, long connecting rods, or cases that have been heavily surfaced.

Constructed from high-grade materials designed to withstand the intense heat and cycling of an air-cooled combustion chamber, these shims act as a stable foundation between your engine case and the cylinder base. Using shims is a far superior method to machining the piston tops, as it preserves the structural integrity of the piston crown and maintains consistent thermal characteristics across all four cylinders. Whether you are building a 1776cc, 1835cc, or 1914cc powerhouse, these shims ensure that your rotating assembly has the breathing room it needs while allowing you to hit your target compression ratio for pump gas or race fuel applications. Don''t leave your engine geometry to chance; use these professional-grade spacers to achieve the perfect "squish" zone for maximum efficiency.

Vehicle and Engine Fitment

This shim set is designed for Type 1 based air-cooled engines utilizing "thick wall" 90.5mm or 92mm cylinder barrels. Please note that these require the engine case to be machined for the larger cylinder registers.

• Volkswagen Beetle: 1950-1979 (Modified with 90.5/92mm cylinders)
• Volkswagen Karmann Ghia: 1956-1974 (Modified with 90.5/92mm cylinders)
• Volkswagen Bus/Transporter: 1950-1971 (Type 1 upright engine configurations)
• Volkswagen Type 3 (Squareback, Fastback, Notchback): 1961-1973
• Volkswagen Thing (Type 181): 1973-1974
• Custom Applications: Sand Rails, Dune Buggies, and Trikes using VW Type 1 based engine cases.

Technical Specifications and Dimensions

• Compatible Bore Sizes: 90.5mm and 92mm
• Shim Thickness: .040 Inches (1.016mm)
• Material: Precision-stamped high-tensile steel
• Set Quantity: 4 Pieces (Complete set for one engine)
• Manufacturer: EMPI
• Part Number: 4559-40
• Placement: Between the engine case cylinder register and the cylinder base

Expert Pro Tips for Installation

1. Always Measure Twice Before Final Assembly

Before you commit to a shim thickness, perform a "dry fit" of your cylinders and pistons. Use a deck height bridge tool or a depth micrometer to measure the distance from the piston crown to the top of the cylinder at TDC. Ideally, for a street-driven air-cooled VW, you want a final deck height between .040'' and .060''. If your measurement without shims is .010'', adding this .040'' shim will bring you to a perfect .050''. Proper deck height prevents the piston from "slapping" the cylinder head at high RPM while ensuring the compression remains high enough for efficient combustion.

2. Proper Sealing Technique at the Base

One of the most common mistakes builders make is using too much RTV silicone at the base of the cylinder. When using these shims, we recommend a very thin, almost transparent smear of a high-quality non-hardening sealant like Curil T or Permatex Aviation Form-A-Gasket on both sides of the shim. This prevents oil "sweating" at the case-to-cylinder interface without creating a thick "gasket" that could compress and change your deck height measurements under the torque of the head nuts. Ensure the case surface and the cylinder base are surgically clean before application.

3. Account for Compression Ratio Changes

Remember that every .010'' of shim thickness changes the volume of your combustion chamber. Adding a .040'' shim increases the deck volume by approximately 2.6cc on a 92mm bore. This will lower your static compression ratio. If you find that your compression is too low after installing these shims, you may need to have your cylinder heads "fly-cut" to reduce the combustion chamber volume and bring the compression back up to your desired level. Always use a CC-measuring kit on your heads and calculate your final ratio to ensure the engine is tuned for the octane rating of the fuel you intend to run.