I talked with Gerhard at AI about the engine. Rod bearings are replaced on an exchange basis. They send your crank assembly out for rebuilding and you get one off the shelf for quick turnaround. I pulled the cylinders off myself and found there was nothing wrong with the bearings. The radial play was nil. The pistons were carboned up and the ring on one piston was stuck in the land. I cleaned it all up using Loctite Chisel gasket remover (per Gerhard's advice), put it back together and ran 3 test flights today. The engine is a lot quieter on a cold startup. The compression is better than it was, but still a little soft. The rings probably got distorted when I removed them from the pistons. I have a new set of pistons and rings on the way from AI. I'll put a little more flight time on the motor to try and break-in the old rings before I put the new set in.

I really don't know why the motor was carboned up from about 400 flights with Redline Allsport synthetic at 50:1. One theory I read about on the net was that outboard boat mechanics found that 87 octane gasoline sold over the last few years is unusually prone to carbon build up. They claim this doesn't happen with 89 octane gas or higher. It isn't the octane rating, but the chemical makeup of the gasoline. I've been running the engine exclusively on 87 octane gas. I'll switch to higher octane and see if it makes a difference in the long term.