At 600 hours I am replacing all 6 pistons, cylinders and rod bearings. The heads are being overhauled.
My engine is almost 3 years old and has been flying for 26 months. It is serial number 33A 1256.
A few months ago I replaced a burned valve. Recently oil consumption has been going way up. Last Saturday the engine used 2 quarts in 5 hours. It was time to find out why.
When I did my annual a few months ago I performed a leak down compression check. All cylinders came in between 65 and 75 which is acceptable. The instructions that came with the gauge suggest that compression be checked at TDC. I can tell you now; that is not good enough.
Last Sunday I did another test. This time I checked compression not just at TDC but also before and after. What I found on some cylinders, and one in particular, is that shortly after TDC, the values dropped off quickly from 70 to 45. Wow that’s way wrong. What is that? Must be some problem with the rings or cylinder. That hissing noise coming from the oil filler tube can’t be a good sign.
I pulled the head and cylinder off on #5, the worst cylinder, and found that the rings were completely frozen in their grooves, in the compressed state. Because the cylinder is a bit tapered, as soon as the piston started down the cylinder, the rings lost contact with the cylinder wall.
I pulled off the other cylinders. Four out of six pistons had one or more stuck rings.
Time to call Jim McCormick. I bought my engine from Jim. Jim owns and operates Jabiru Pacific
which is based in Fresno California. He has has helped me before. One day I was flying past Fresno on my way to Arizona. I did an in-flight mag check and was astonished to find I was flying on one magneto. I called Jim on my cell phone, while I was flying, and he told me to come on in, so I diverted to Chandelier field. He had me fixed up in no time and I was on my way.
This time I drove
to Chandelier field with three boxes of parts. Jim and I went over them. The heads are not too bad but since they are off the engine, we decided to give them the full treatment to get them back into shape. It should be noted that one more exhaust valve was showing early signs of leaking. Also one of the heads had been leaking. I have been careful about torquing my head bolts, especially when the engine was new, but I guess I was not careful enough.
There is an improved piston design with wider ring grooves. I will be upgrading to these. The cylinders have odd wear patterns. Jim is contacting the factory about them.
My oil pressure is down to 26 PSI. The rod bearings look warn and they are not expensive so I am replacing them.
It’s important to note that the rings are stuck with carbon deposits. This is the result of oil oxidizing. The oxidizing has occurred because of high operating temperature. I am replacing the oil cooler which came with the engine with one that is twice as large but bolts into the same place and does not require major cowing rework. I am also going to switch to Aeroshell 15W-50
year round. This oil is over %50 synthetic and stands up better under high temperatures. I had been using Aeroshell 100 Plus
in the hot summer months and the 15W-50 in the winter.
I love the way my Jabiru engine performs; its smooth, powerful and light weight. It has powered my plane safely all over the United States. I hope after these repairs I get more than 600 hours out the engine before my next major overhaul.