So I've read about cylinders cracking on this engine.
Have all of the cracks happened to engines that had the collector ring exhausts?
Does the collector ring have slip joints to allow movement between the cylinders?
If not, then you are just asking to crack something as the engine heats up and then cools back down the dimensions change between the cylinders.
Full scale aircraft engines have provisions to prevent cracking of engine components, including the exhaust itself, built into the exhaust system.