LETTER TO THE EDITOR
Just read Ask Paul’s post (A puzzling compression problem) and it reminded me of an problem I found several years ago. I had a Lycoming IO-360 180 hp in a Pitts that began to use some oil. It increased gradually from a quart in 15 or 20 hours to 10, then eight, then on one trip it went to about a quart in three to four hours. The compression was good in the low 70s over 80, so thought I must have broken oil rings.
First I pulled a cylinder with a slightly oily plug expecting to hear the tinkle of ring parts on the shop floor, but heard only a click as the oil ring slid out intact. Not until I got to the top ring did I hear the tinkle on the floor: A broken top ring. I pulled all cylinders to find a broken top ring in each. A little concerning, since the only real indication was a rise in oil consumption, not low compression. All top ring groves were worn beyond limits.
If I remember right, it had only about 800 hours SMOH, however a Pitts engine with a fixed pitch prop does live a tough life.
I thank you for your articles and look forward to more.
STEVE SOPER, via e-mail
Sounds like cermichrome cylinders. 800 hours was about the life of the top of a cermichrome cylinder. The plating would tear out of the top of the cylinder due to lack of lubrication, and cause the upper ring to fail. I’ve seen the exact same failure as well. Compressions were still passable, but upper rings were all broken. A closer exam showed the top end torn out of each of the cermichrome cylinders.