From LeadSled...
The story of the R-2800 is very interesting, in the development/early production days, there were severe harmonic vibration problems, but some very smart people got to the bottom of the problems --- and the engine in service developed the good reputation mentioned here. For anybody of an engineering bent, the development story, and harmonics never observed before, and their cure, is a fascinating story.
The story is here... a great read for those interested in the technicalities;
http://www.enginehistory.org/NoShort...Crankshaft.pdf