Piston Ring Set, 90.5mm, 2 X 2 x 4.75, for Aircooled VW

OVERVIEW

When you are building a performance-oriented air-cooled engine, the seal between your pistons and cylinder walls is the absolute foundation of your horsepower and engine longevity. These Grant 90.5mm Piston Rings are engineered specifically for the high-demand environments of a 1776cc or larger big-bore displacement build. Unlike generic off-the-shelf rings, these are manufactured to exacting tolerances to ensure that your combustion pressure stays exactly where it belongsabove the piston crown. Whether you are refreshing a tired weekend cruiser or assembling a brand-new high-revving street engine, these rings provide the necessary radial tension and heat dissipation to keep your oil temperatures stable and your compression ratios consistent across all four cylinders. You won''t find a more reliable way to ensure your engine stays leak-free and powerful under the hood of your classic Volkswagen.

The specific 2mm x 2mm x 4.75mm configuration is a classic standard for many high-quality aftermarket 90.5mm piston sets used in the VW industry. The top compression ring is designed for maximum heat resistance and rapid seating, while the secondary ring acts as a crucial "wiper" to manage the oil film on the cylinder walls and provide a secondary seal against blow-by. The 4.75mm oil control ring is the workhorse of the set, featuring a robust expander design that prevents excessive oil consumptiona common headache in air-cooled Volkswagens that see high operating temperatures. By choosing these Grant rings, you are investing in a product that resists "ring flutter" at high RPMs and maintains its structural integrity over thousands of miles of heat cycles, ensuring that your Beetle, Bus, or Ghia remains as reliable as the day it left the factory, even with the added stresses of a performance-tuned big-bore kit.

FITMENT

This piston ring set is designed for Aircooled VW Type 1, 2, and 3 engines equipped with 90.5mm Big Bore piston and cylinder kits. Common applications include:

• Volkswagen Beetle: 1950-1979 (With 90.5mm Big Bore Kit)
• Volkswagen Karmann Ghia: 1956-1974 (With 90.5mm Big Bore Kit)
• Volkswagen Bus / Transporter: 1950-1971 (With 90.5mm Big Bore Kit)
• Volkswagen Type 3 (Squareback, Fastback, Notchback): 1962-1973 (With 90.5mm Big Bore Kit)
• Volkswagen Thing: 1973-1974 (With 90.5mm Big Bore Kit)
• Custom Sand Rails and Dune Buggies: Utilizing 1776cc, 1914cc, or 2110cc engine configurations with 90.5mm bores.

SPECS

Detailed technical specifications for the G1990 Piston Ring Set:

• Bore Diameter: 90.5mm (Standard for 1776cc and larger builds)
• Top Compression Ring Thickness: 2.0mm
• Second Compression Ring Thickness: 2.0mm
• Oil Control Ring Thickness: 4.75mm
• OEM Reference Number: 311-198-16991
• Material Composition: High-grade cast iron and steel alloy for superior heat dissipation.
• Quantity: Complete set for four (4) pistons.
• Surface Finish: Precision-ground for accelerated break-in and seating.

PRO TIPS

1. Always Verify Your Ring End Gap

Even though these rings are manufactured to high standards, you must never install them straight out of the box without checking the end gap. Place each ring into its respective cylinder (use the piston to push it down about an inch so it stays square) and use a feeler gauge to measure the gap. For a 90.5mm bore, a general rule of thumb is .004 inches of gap for every inch of bore diameter. If the gap is too tight, the ring ends can touch as they expand from heat, leading to catastrophic engine failure and broken ring lands. Don''t skip this step; it is the hallmark of a professional engine builder.

2. Stagger the Ring Gaps Correctly

Proper orientation of the ring gaps is vital to preventing "blow-by" and ensuring high compression. When installing the rings onto the piston, ensure that the gaps are staggered so they do not line up. A common practice is to space the gaps 120 degrees apart or at the 12, 4, and 8 o''clock positions. Avoid placing any ring gap directly over the piston pin hole, as this can lead to uneven wear and oil consumption. Always double-check that the "Top" or "Dot" mark on the compression rings faces toward the combustion chamber (upward) to ensure the taper functions correctly.

3. Use Proper Break-In Oil

The first 500 miles are the most critical for the life of your new piston rings. To ensure these 90.5mm rings seat perfectly against the cylinder walls, use a high-quality, non-synthetic break-in oil with high ZDDP (zinc) content. Synthetic oils are often too "slippery" and can prevent the rings from wearing in properly, leading to glazed cylinder walls and permanent oil burning issues. Avoid sustained idling during the initial start-up; vary your RPMs and use engine braking during the first few drives to create the necessary cylinder pressure to force the rings against the walls for a perfect seal.