Oil Feed To Number 4 Main Bearing

This Service Bulletin applies to all Type 1 engine cases. Any case purchased from any company - aircraft or automotive related - will have this restrictor plug in it - per the VW design.

The restrictor plug is pressed into the case to restrict the flow of oil to the Number 4 main bearing. If any debris accumulates in back of the plug it will block the flow of oil to the bearing. In the VW Beetle, the only load on this bearing is the pulley that drives the fan and the alternator - via a belt. Approximately a load of 4 hp!

If the flow of oil is blocked or restricted the number 4 bearing will wear out quickly. The nose of the crankshaft will not be supported any longer. After "X" number of repeated oscillations (hours), your crankshaft may break at the nose of the crank.

Drill and Tap #4 Oil Feed
Instructional Movie

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The solution: Prior to assemblying engine, for all new cases, is to drill and tap the pipe plug that feeds the Number 4 main bearing. The drill size is 21/64" and the tap size is 1/8" pipe thread. This procedure has been done to all GPASC cases sold since 1999, but again, applies to any Type 1 engine case manufactured at or around the date posted.

Area involved noted above.
In addition, it is reasonable to drill and tap any case that is dis-assembled for any reason, to check for proper oil flow, irregardless of engine manufacturer or case supplier.

How to check for oil flow to the Number 4 and Number main bearing:

With the oil feed hole drilled and tapped; take a piece of welding rod or a straight coat hanger, and cut 2 straight pieces that are 12" long. One piece is placed down the Number 4 oil feed hole that is drilled and tapped, and the other piece is placed down the Number 3 main bearing oil feed hole (right behind the cam timing gear). The two pieces of wire should touch inside the engine case.

An additional check can be made by using two fingers to block off the oil feed holes in the engine case. You can then blow into the drilled and tapped hole in the engine case. Air should escape. If it does not, one or the other hole is still plugged.

In some cases when you drill the plug out, a part of it will be moved to the back of the oil feed hole located at the bottom of the Number 3 main bearing oil feed. This need to be checked. If this happens, you will need to remove the case studs that are on either side of the oil feed hole, and drill the plug out through the Number 3 oil feed hole with a drill bit, just under the size of the oil feed hole.

If you have any further questions or comments, please contact Great Plains Aircraft (telephone numbers & email listed below).

Type 4 VW Engines Utilizing 66mm or 71mm Crankshafts

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Great Plains Aviation Supply LLC
7011 N 160 Avenue
Bennington, NE 68007
Orders: 1-800-922-6507 (available in the US Only)
Information: 402-493-6507
or Fax 402-493-3846