Compression
in General Tech Discussion
8 years ago
During pre-flight today while pulling the prop through to purge the oil sump, one cylinder was obviously lacking compression (perhaps 1/3 normal by feel), an obvious “dead” cyclinder every 4th compression stroke. So (after completing the oil purge and level check) I decided to start the engine to warm it for a compression check and to see if it would start and run, which it did; and it ran normal. Normal mag check, normal full power RPM. After warming and shutting down, I checked the compression. But before I did, I pulled the prop through again and found that there was no “dead” cylinder compression-wise. Everything had returned to normal. Compression ended up being all between 135 and 155.
My question is what happened? Is this normal or a failure waiting to happen? Should I worry. I run fresh 93 octane auto gas. I suspect it was a stuck valve. We have had that on Aeronca Champs, but they would hardly run with a stuck valve. The A&P mixed Chevron Techron in the tank and this cleared the stuck valve on the Champs.
Now I worry about what is happening to my Rotax and if I there are any other diagnostics I should perform before flying. It never did this before.
My question is what happened? Is this normal or a failure waiting to happen? Should I worry. I run fresh 93 octane auto gas. I suspect it was a stuck valve. We have had that on Aeronca Champs, but they would hardly run with a stuck valve. The A&P mixed Chevron Techron in the tank and this cleared the stuck valve on the Champs.
Now I worry about what is happening to my Rotax and if I there are any other diagnostics I should perform before flying. It never did this before.
