Originally Posted by
av8tor1977
You haven't considered the tension of the rings, which may have been significantly lowered from a hot lean run. Also, and equally important is the ring gap. It should be .003 to .005". The blow by staining indicates to me that the rings definitely were not sealing well. I would add new Bowman rings for sure. What's 22 bucks to make your engine run better and last longer, especially since you have it apart now anyway?
Before re-assembly with new rings, I would take some Scotchbrite and acetone or carb cleaner spray and clean those pistons up. Lots of people like to use synthetic from the start nowadays, but I'm still an old fashioned fan of using dino oil for break in.... Why delay the all important break in by running synthetic oil and risking glazing the cylinders and never getting a good ring seal?
AV8TOR
As I said early on, the goal is to get it up and running for a contest in 8 days from now. There is no way to send Frank a piston and cylinder and have him custom cut me a set of rings and get them run in and be able to make the contest. Let alone having him do a one off set for only 22 bucks. My intuition is telling me that I just pushed the engine a bit too hard before the rings got fully seated. Remember it only has 5 gallons through it. That was enough for the DA 150 engines I have had but maybe not enough on this particular engine. That may sound like a lot of fuel but this airplane carries 1/2 gallon. The cylinder bores still have good cross hatch pattern to them as well. I would tend to agree that the rings may not be sealing as well as I would like them to but I think it's because they are still relatively new and not damaged. Give me a day or two and I will publish an update. I do appreciate the feedback though.