Main Bearings, .040 Case, .030 Crank, .080 Thrust

OVERVIEW

When you are deep into a performance engine build or a vintage restoration, you quickly realize that the heart of your air-cooled Volkswagen relies entirely on the precision of its internal clearances. These IAP Main Bearings are engineered for those specific "rescue" scenarios where a standard bearing simply won''t cut it. Designed for cases that have been line-bored to .040 inches (1.00mm) over and crankshafts that have been turned down to .030 inches (0.75mm) under, this set provides the exact tolerances required to restore oil pressure and engine longevity. In the world of VW engine building, saving an original German magnesium or aluminum case is a priority, and having access to these specialized "double oversize" thrust dimensions allows you to keep that numbers-matching block in service rather than sending it to the scrap heap.

The standout feature of this particular bearing set is the .080 inch (2.00mm) oversized thrust surface. In many high-mileage Type 1 engines, the constant pounding of the crankshaft against the case web causes the thrust surface to widen significantly. A standard or even a .040 thrust bearing often isn''t enough to bridge that gap. By utilizing a .080 thrust cut, you are able to machine the case back to a perfectly flat, square surface, ensuring that your crankshaft end-play remains stable even under the pressure of a heavy-duty pressure plate. Manufactured with a high-strength steel backing and a durable bearing alloy face, these bearings are built to withstand the unique heat cycles and lubrication demands of the air-cooled flat-four environment.

FITMENT

This main bearing set is designed for Volkswagen Type 1 based engines, including the following models and years:

• Volkswagen Beetle: 1961-1977 (Standard) and 1971-1979 (Super Beetle)
• Volkswagen Karmann Ghia: 1961-1974
• Volkswagen Bus / Transporter: 1961-1971 (Type 2 with 1200cc, 1500cc, or 1600cc engines)
• Volkswagen Type 3: 1962-1973 (Squareback, Fastback, Notchback)
• Volkswagen Thing: 1973-1974
• Custom Applications: Ideal for Sand Rails, Dune Buggies, and Trikes utilizing a 1600cc-based upright engine case.

SPECS

• Brand: IAP (International Auto Parts)
• Case Bore Size: .040 inches (1.00mm) Oversize
• Crankshaft Journal Size: .030 inches (0.75mm) Undersize
• Thrust Surface Size: .080 inches (2.00mm) Oversize
• Material: Heavy-duty steel backing with high-grade Babbitt/Aluminum alloy lining
• Engine Type: VW Type 1, 2, and 3 (1200cc to 1600cc based)
• Part Number: 111-198-487OS+2
• Kit Includes: Full set of main bearings including the flanged thrust bearing

PRO TIPS

1. Always Verify with a Micrometer

Never assume that your machine shop and the bearing box are in perfect agreement. Before beginning your assembly, use a high-quality micrometer to measure your crankshaft journals and a dial bore gauge to check the line-bore in your case. Even the best parts can be boxed incorrectly, and catching a clearance issue on the bench is much easier than catching it after the case halves are torqued together. You are looking for that "sweet spot" of oil clearance to ensure your engine doesn''t run too tight and seize, or too loose and lose oil pressure when hot.

2. Prep the Thrust Surface and Oil Galleys

When using a .080 thrust bearing, your machinist must cut the case thrust surface to match this specific dimension. After machining, it is critical to "de-burr" the oil holes and the edges of the bearing saddles. Use a small file or a deburring tool to ensure there are no sharp edges that could snag the bearing shell. Additionally, because line-boring creates a massive amount of metal shavings, you must pull all oil gallery plugs and "hot tank" or pressure wash the case multiple times. A single piece of leftover aluminum or magnesium grit will ruin your new bearings in seconds.

3. Proper End-Play Adjustment

Setting the crankshaft end-play is the final critical step when using oversized thrust bearings. With the .080 oversized thrust surface, you must ensure that the bearing is seated fully against the machined surface of the case. Use a dial indicator to measure the fore-and-aft movement of the crankshaft. You should aim for a spec of .003 to .005 inches of end-play for a street engine. If you find you have too much or too little, you must adjust using the three shims behind the flywheel. Never run an engine without verifying this, as an incorrect thrust clearance will lead to rapid bearing failure and potential case damage.