Mack Boring
I talked to the guys at the Mack Boring parts counter, including a guy running the engine rebuilding class. Their take:-its obvious when they're gone. The rubber disintegrates.-engine alignment is art rather than science.On my 19 year old Hunter, they recommended letting sleeping dogs lie unless there was a problem (e.g. lots of vibration; bits of rubber around; too much play in the engine.) Of course, this was in the context of discussing a motor that only gets 20-30 hours of use per year.