VW Type 1 Main Bearing Sizing Chart for VW Beetle & Dune Buggy Engines

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This post covers main bearing sizing for VW Type 1 engines. This post features a chart for sizing and measurement reference.

Main bearings are an important part of your air-cooled VW engine's bottom end. 

A properly sized main bearing allows your crankshaft to move freely, without too much play.  A correctly sized main bearing is also important for maintaining proper oil pressure. 

We have seen many customers have problems with supposedly rebuilt engines that have bearings that are too tight, or too loose.  Both can lead to catastrophic failure in short order.

It's important to make sure that your measurements are correct and match factory VW specifications to ensure that your rebuilt engine survives past the first fireup. 

 

Crank Measurements   Bore Measurement   Thrust Measurement
Stock 2.164   Stock 0 mm (2.559") Stock 0 mm (.864")
0.010" Under 2.154   0.020" Over .50 mm (2.579") 0.040" Under 1.0 mm (.824")
0.020" Under 2.144   0.040" Over 1 mm (2.599") 0.080" Under 2.0 mm (.784")
0.030" Under 2.134   0.060" Over 1.50 mm (2.619")    
0.040" Under 2.124   0.080" Over 2.00 mm (2.639")    

 

There are three measurements you have to take on any air-cooled VW engine case to properly size your main bearings.  The chart above shows the common sizes for these measurements.

First you have to determine if your crankshaft has been turned or is stock size.  If you have a new VW Type 1 crankshaft, whether it's a stroker crank or stock crankshaft, it will be machined to the standard size of 2.164".  If your crankshaft has been used or reground it is a good idea to measure it or ask your machinist to measure the journals. Air-cooled VW cranks can be machined as small as .040" under the standard size.  We recommend getting a crankshaft as close to stock size as possible.

The next measurement required is the engine case main journal bore.  You can measure this by measuring the inner diameter of your engine case main journal without the bearing, while the case is bolted together.  You can also measure the journals of one case half by measuring the diameter of the open end of the journal at the engine case center line.

Most VW Type 1 engine cases are a combination of magnesium and aluminum, making them soft and subject to distortion after years of use.  This means they often require an align bore to ensure all of the main journals are perfectly round and the same size. Engine case main journals can vary due to machine work or wear over the years. It's always a good idea to measure the main journal bore of a used engine case you would like to purchase to ensure that it is useable.  

Standard size for main journal bore is 2.559".  They can be bored as much as 0.080" over.  Again we recommend using an engine case that has the least amount of material removed from it as possible for longevity. 

Main journal thrust is the final measurement that must be performed when sizing your air-cooled VW main bearings.  The thrust measurement is determined by measuring the thickness of the last main journal on the flywheel end of the engine.  The stock measurement for thrust is 0.864" and it can be cut as much as 0.080" under. 

The thrust main bearing takes the engine's forward and aft load, otherwise known as thrust, from the clutch and drivetrain. Thrust can wear out on a VW Type 1 or Type 4 engine due to age, improper flywheel endplay settings or hard driving with a heavy clutch. With that being said it may take a varied amount of time to wear the thrust one way or another.  Factory thrust spefications with the flywheel installed is .003" - .005".

A common health test many engine builders and VW nuts like to perform on an engine is to grab the engine's crank pully and tug it forward and push it backward to see if there is any noticeable play.  If you can feel noticeable play the thrust is likely worn on the bearing or case. 

One final note is that measurements for main bearings can be either taken in inches or millimeters. A conversion chart is included so that your measurements jive with the metric or US measurement systems. 

    Metric to Inches Conversion      
    .25 MM = .010" 1.00 MM = .040"      
    .50 MM = .020" 1.50 MM = .060"      
    .75 MM = .030" 2.00 MM = .080"