I am lucky to play with just about every size and style engine in common use, the Perkins engines (CAT) are very well built and must be the cheapest engines about to rebuild, the 3 cylinder 152 unit can have new piston/liners (sleaves) bearings and gaskets for about £230, some people call them "Ships Anchors" but not on this side of the Pond, in numbers alone they would be way ahead possibly double ahead of any other engine, the CAT 333c and 3306 unit is a very simple unit, they like to come to bits every few years, again this engine is cheap to repair with Non OE parts that are of good quality and you dont need any fancy tools to tackle them generaly, Cummins L10/M11 and Big Cam 14 litre engines are built using a now common style fuel type system "common rail" the Cummins pressure time (PT) fuel system is a great design item the Jacob's Brake is something that should be fitted by Law to every Diesel built, but the engine is fairly technical in its construction, its the small details that make them run well, this realy takes them outside the average Saterday afternoon spanner man scope, I hear on this Forum lots of 5/6 inch pound talk????, the Detroit thing I dont understand as all the 53 and 71 series engines I have worked on are fairly complex, the last unit I touched was a V16-71 this is 2 V8's poked together, 4 valve head plus all those turbo's and blowers and a cam shaft running at crank speed, then liners with about ten different fit spec's, the average fitter would be well out of his patch, a very famous engine from the past in the U.K. was the Gardner 180 and 240 this was a real Gaffer's engine good on fuel and ran for ever, it had shrouds on the inlet valves, the injector pump was a thing to admire, but they came from a time now gone into the past, Duetz engines the air cooled sort are great and stong runners, the blower fan only has to shift 1/3rd of the wind of a water cooled engine to keep its self running in the green, they are well built and well liked by anyone that has run them, but the little 3 pot Perkins has to be king of all it does, its only a small engine but has great Heart.
