High Mileage Magnum

I have dismantled a few 360 Magnum engines and the results were very consistent. Anything with poor oil change history had really bad carbon deposits and/or sludge. The oil drain holes in the piston ring grooves are always blocked with carbon. The main rod bearings usually have some of the copper backing showing through the soft bearing surface. The cam bearings usually start flaking apart, or random bits or chunks of the soft bearing surface is missing. The pushrod ball ends at the rocker arms and the mating ball cup in the rocker arms are often scuffed badly. Usually the engines with scuffed pushrods also had scuffed valve tips. About half of the camshafts had at least one lobe where the metal was flaking off the cam lobe leaving behind a small pot hole in the lobe. The cylinder bores always have much more wear with a good sized ridge at the top and the rings have very little tension remaining. The cylinder heads on most Magnum engines will develop cracks between the intake and exhaust valve seats eventually regardless of maintenance. This does not mean the Magnum engines won't keep running a while with this kind of wear. What it really means is, if you have a running engine with little or minimal signs of carbon or sludge build up looking inside the oil filler cap, or in the lifter valley area if you have the intake manifold removed, you have a better chance of scoring an engine without most of these issues. If a budget allows machining costs, new pistons, new camshaft, new cylinder heads, and new rocker arms and pushrods, then high milage engines are perfectly fine. If it's a tight budget build, just know that if you take it apart you may have to, at minimum, replace all cam, main, and rod bearings, ball-hone the cylinders to deglaze them, clean and scrape out all carbon from the piston ring lands, replace piston rings, and replace the camshaft and oil pump intermediate drive shaft. As for cylinder heads, if you're lucky enough to find no scuffed valve tips, you can almost always ignore the cracks and hand lap the valve seats so seal again, but you'll have wider seat margins than recommended, and you'll still be limited to around .515-.520 valve lift unless the guides are cut down for clearance. New valve springs are mandatory for any performance camshaft install. If it was a running engine with good maintenance history, meaning lots of oil changes at 4,000 mile intervals or less, most of this won't be a problem. If it's a higher mileage engine, came out of truck used for lot's of heavy towing, or had poor maintenance history, you may still get plenty of life out of it anyway, but these are problems that will show up once you start taking it apart. If you run it and have bearing failures in a few thousand miles, just get another engine and try again since they are cheap and plentiful. Sorry for the long-winded post, but there is no short way to say it without sounding negative.