My Wooden Airplane
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5/5/2012 - 5/10/2012

5th Bearing

The 5th bearing is, in my opinion, the key to converting the Corvair engine for aircraft use. The crankshaft in a stock Corvair engine is supported by 4 main bearings, but it is not intended to support the loads of a spinning propeller. So an additional (5th) bearing is sandwiched between the crank flange and the prop hub (and can be seen here).

The bearing itself fits over the snout of the crank flange, but it needs to be aligned. Apparently, there is some variation in the manufacture of the crank flanges, so the bearing needs to be centered. It is done using these three "jaws" on the back (kind of like the jaws of a drill press, except that they are individually adjustable).

The alignment procedure requires that a dial indicator be rigidly mounted to the case. The idea is to rotate the crankshaft slowly, watching the dial indicator and tightening the set screws on the front side of the bearing until the total runout is less than .001 inches. It took me several attempts, but I was able to get it within .0004 inches!

Next, the housing needs to go on. Those orange strips in the photo below are called clearance film. They ensure that a specific clearance exists all the way around between the bearing and the housing. With those strips temporarily held in place, the housing slips over the bearing and is then bolted to the case.

(I forgot to take a picture of it at the time, so here is one from later in the
assembly process. It uses the same bolt holes as the transmission bell housing.)

The next step is to install some alignment pins to make sure the housing goes back into the correct position in case it ever gets removed. However, it requires some special tools that I don't have at the moment, so I'm just leaving it bolted on for now.

Total Time: 6.0 hrs.