For most people determining the right bearing size can be a bit confusing. There are lots of sizes to choose from and getting the right bearings for your build is critical. To determine the correct bearings required for your engine rebuild, you will need to know a few different measurments. In this article we will cover the most basic measurements for the engine case (align bore size and thrust cut size) and for the crankshaft (main journal size and rod journal size).
Volkswagen listed all bearing measurements in millimeters.(Machine shops didnt always use millimeters and may give you the measurements in inch!)

Engine Case Bearings:

There are two different measurements you will need to know regarding the engine case. These measurements are commenly refered to as the “align bore” and “thrust surface” or “thrust cut”. If you are replacing old bearings without machining your case, then you will be able to measure the old bearings outer diameter to determine the current align bore. You will also be able to measure the distance between the flanges of the thrust bearing to determine its thrust cut. If you determine the case needs to be machined, you will need to ask the machine shop the finished size on the align bore and/or thrust cut. Some shops may provide this information by attaching a tag or stamping the align bore into the case. If your not sure just ask!

Align Bore Size

A standard Volkswagen engine case bearing saddle size is 65mm this also can be measured as 2.560in depending on your location. When measuring the bearing this would be the bearing outer diameter (or o.d.).
(Example: You measure the bearing outer diameter and it measures 66mm/2.600″ this indicates your case has been align bored 2mm/.040″ or 2nd Oversize.)

Thrust Cut Size

As engine cases are reused some may require the thrust surface of the rear main bearing to be cut, when this happens it requires a special oversized thrust bearing. A standard Volkswagen engine case bearing saddle between the two flanges on the thrust bearing (flywheel end of crankshaft) is 22mm. When a machine shop cuts the thrust surface of the case it then requires a bearing with a thicker thrust flange. This is commenly refered to as an oversized thrust bearing. These bearings are available in plus 1mm (refered to as “OS” on the end of the part number) and plus 2mm (refered to as “OS2” on the end of the part number).
(Example: You measure the distance between the flanges on the thrust bearing and it measures 21mm this indicates your case has been thrust cut 1mm or 1st Oversize.)

Crankshaft Bearings:

There are two different measurements you will need to know regarding the crankshaft. If you are replacing old bearings without machining your crank, then you will be able to measure the old bearings outer diameter to determine the current align bore and the inner diameter to determine the main journal size. If you determine the crank needs to be machined, you will need to ask the machine shop the finished size on the main journals as well as the rod journals. Some shops may provide this information by attaching a tag, stamping the journal sizes into the crank or paint markings. Again if your not sure just ask!

Main Journal Size

A standard Volkswagen crankshaft main journal size is 55mm this also can be measured as 2.165in depending on your location. When measuring the bearing this would be the bearing inner diameter (or i.d.). When measuring the crankshaft this is would be the journal outer diameter (or o.d.).
(Example: You measure the bearing inner diameter and it measures 54.75mm/2.155″ this indicates your crank has been machined .25mm/.010″ or 1st Undersize.)

Rod Journal Size

A standard Volkswagen crankshaft rod journal size is 55mm this also can be measured as 2.165in depending on your location. Measuring a rod bearing really isnt the best way to determine the rod journal size, it is best to measure the rod journal on the crank. When measuring the crankshaft this is would be the journal outer diameter (or o.d.). Something to whatch for when measuring your rod journals, Porsche and Chevy rod journals have also been used. Porsche journals were used “back-in-the-day” and are not very common now. Chevy rod journals are very common in larger engine combos using a longer stroke (82mm-86mm).
(Example: You measure the rod journal outer diameter and it measures 54.75mm/2.155″ this indicates your crank has been machined .25mm/.010″ or 1st Undersize.)

Based on the examples above we can now determine the correct bearing sizes we need for our build. We have determined that we need a main bearing that measures 40(.040) on the case and has an oversize thrust while measuring 10(.010) on the crank. We aslo determined we need a rod bearing that is 10(.010) 1st Undersized

Volkswagen Case & Crankshaft Main Bearings:

Crankshaft Main Bearing Journal Diameter
(Bearing Inner Diameter “i.d.”)
Case Bearing Saddle Diameter
(Bearing Outer Diameter “o.d.”)
Standard
55.00mm
2.165″ (i.d.)
1st Undersize
54.75mm
2.155″ (i.d.)
2nd Undersize
54.50mm
2.145″ (i.d.)
3rd Undersize
54.25mm
2.135″ (i.d.)
4th Undersize
54.00mm
2.125″ (i.d.)
Standard
65mm (o.d.)
2.560″ (o.d.)
STD/STD STD/10 STD/20 STD/30 STD/40
1st Oversize
65.50mm (o.d.)
2.580″ (o.d.)
20/STD 20/10 20/20 20/30 20/40
2nd Oversize
66.00mm (o.d.)
2.600″ (o.d.)
40/STD 40/10 40/20 40/30 40/40
3rd Oversize
66.50mm (o.d.)
2.620″ (o.d.)
60/STD 60/10 60/20 60/30 60/40
4th Oversize
67.00mm (o.d.)
2.640″ (o.d.)

 

Volkswagen & Chevy Connecting Rod Bearings:

Crankshaft Rod Bearing Journal Diameter
(Bearing Inner Diameter “i.d.”)
VW Rod Journal Chevy Rod Journal
Standard
55.00mm
2.165″ (o.d.)
Standard
2.000″ (o.d.)
1st Undersize
54.75mm
2.155″ (o.d.)
1st Undersize
1.990″ (o.d.)
2nd Undersize
54.50mm
2.145″ (o.d.)
2nd Undersize
1.980″ (o.d.)
3rd Undersize
54.25mm
2.135″ (o.d.)
4th Undersize
54.00mm
2.125″ (o.d.)