I know everyone here knows my option by now, with a single vs. a twin. Many people make the mistake of thinking the engines mass is directly related in how long the engine will last and in "most" cases this is fact.
I have an older model Isuzu LB1 3 cylinder engine, (with a cast iron block and head, new ones have an aluminum block) as my heavy duty backup system, to my 14/1 and 16/1. With an Amsoil bypass system on it and marine exhaust manifold for rapid warm ups and conventional radiator.
Like this one:
http://cgi.ebay.com/ebaymotors/24hp-Isuzu-3LB1-Diesel-Marine-Engine-NOS_W0QQcmdZViewItemQQ_trksidZp1742Q2em153Q2el1262QQcategoryZ50441QQihZ024QQitemZ370107138725This engine weighs under 300 lbs. plus the generator and I would bet anyone this little 1,124 cc engine can outlast any Lister type engine between rebuilds, three times over. Don't get me wrong, I love my big singles.
But I have been working with engines "many years" and the point I'm trying to rely is that, not always the engines mass will dictate how long an engine will last. There are other contributing factors that have to be considered, such as how well the block, head and internal components are made.
My 14/1 and 16/1 will need a rebuild before a 6/1 would, but they will surely outlast a twin between rebuilds and can be done in an afternoon, at half the price.
That triple cylinder engine shown, I don't know much about. They may not possess the problems the twin Lister types have and might be very robust. If I had no choice but to pick a a high powered diesel engine beyond the singles,
I would use this proven engine hands down : Â
http://www.deere.com/en_US/rg/ESC/SpecSheet/Ind/3029DF150_C_S0_R0.htmlLook where the maximum torque occurs,1,000 rpm. Put a 6 pole Marathon alternator on it with its 100,000 hour bearings, makes for a "bulletproof 1,200 rpm genset".
Diesel Guy