ORIGINAL: cutaway
If you're only getting 5gal out of an engine, then there's something wrong. It's too lean and burning up the P/L and other wearing surfaces, or maybe the fuel doesn't really have enough oil, or it was half wrecked during breaking it in.
What is a typical failure mode when they die? Loss of compression? bearing failures? mechanical breakage? Seizing?
accually thats fairly normal, Ive seen people get lucky and get 10 but ive also seen people only get a couple but that's normally User error.