My Wooden Airplane
Skip Navigation Links.


Remove Top Cover and Rod Caps

At the suggestion of some of the CorvAircraft members, I removed the top cover and spun up the oil pump with an electric drill. A lot of oil was seeping out of main bearing #1. I don't if it would be considered "excessive", but it makes sense that this bearing has the most flow, since it is closest to the pump. Then I started rotating the crankshaft, and noticed that as each rod bearing came up to the "12:00" position, it would start flowing oil, too. Not as much as the #1 main bearing, but certainly noticable. But then I noticed something else. There seemed to be a lot of "play" or "slop" in the rod bearings. It turns out I could rotate the crankshaft about 1/2 degree (1/4-inch measured at the tip of my 64-inch prop) without the pistons moving at all. That certainly seemed excessive. Also, as I rotated the crank back and forth within that 1/4-inch span, I could see the flow increasing and decreasing, and I could watch the oil pressure gauge rising and falling in time with my movements. I think I found my culprit!

So I removed the rod caps to examine the bearings and measure the rod journals. I wanted to make sure I didn't have an undersized crank with standard bearings, or something similar. Using a micrometer, I verified that the crank was ground .010 undersize (actually, it might have been closer to .012 or .013 undersize). Then I examined the bearing shells, and there is an ".010" stamped on the back, so it appears that I have the right bearings. But look at the wear! This is after only 1.0 hours of runtime! I don't think the old, nasty bearings that I took out of the motor when I first disassembled it looked this bad. Clearly, I had done something wrong, but, at the moment, I have no idea what that might be.

Update: I pushed the bearings closer together and took a close-up (or at least, closer) picture. They are in order, #1 (closest to the oil pump) on the left, and #6 on the right.

Also, I took a picture of the micrometer that I used to measure the journals with,
along with the "standard" that came with the set.

Total Time: 1.5 hrs.