Updated: Jan 3, 2021
before purchasing any old car or mystery core engine, the price of the purchase should reflect the worst case scenario regarding any unknown mechanical conditions. when purchasing a rebuilt engine, paperwork from a reputable shop with the list of work and parts replaced on it, should come with it, documented. without that, it should be treated no different than a mystery core out of a car in a field. from personal experience, we have had better luck with junkyard cores than customers who bring us undocummented "rebuilt" engines. when buying an old car that hasn't ran, always assume the the car got parked and abandoned for a reason, and try to identify what that reason is, right off the bat. chances are, any 60+ year old engine has a lot of wear and tear, irrelevant to mileage. 75% of a street engines wear and tear is related to cold dry starts, followed by excessive idling. its not uncommon to see completely worn out 60k mile engines for that reason. rebuilt, with todays fuel and engine oils (with zinc) theres no reason why you cant get 200k miles out of one. the only way cam lobes, chain, fuel pump cam, cylinder walls, rings, wrist pins and piston skirts get oil is from being thrown off the crank at higher rpm. avoid purchasing a locked up nailhead, as they are locked up from water exposure 9 times out of 10. the cylinder heads are the most valuable part of a nailhead, as they get ruined from water damage due from the inhability of safely replacing the valve seats. water jacket is too close to the valve seats on these engines. especially on the 322/264 heads. even if the machinist doesnt crack the head upon seat install, theres still a much more than likely chance the heads will crack later on under normal use, whether its 2 weeks later or 7 years later.
using a garaged purchased old man car thats sat for 20 years as an example. first thing you want to do is disconnect the fuel line and clamp it. pull the spark plus and squirt oil or any penetrating oil of your choice to soak cylinders (everyone as a type they prefer). pull distributor and prime oil pump with a drill. now try to turn the engine gently by hand to insure it isnt locked up. doesn't hurt to pull off valve covers and look for frozen valves. if it is locked up, typically, (but not always) its from water damage. once an engine is locked up from water related damage, then the damage is done. the engine isnt going to magically be brand new because you were able to free it up, and should be dissassembled to identify the damage that was done. never try to use the crank bolt to break loose an engine. use the ring gear with a prybar, as you have far less flex and multiplied leverage on the ring gear. start removing the valve covers and disasembling rockers from head, and so on until the reason for the engine being locked up is identified and isolated. if its not locked up, and after turning the engine multiple revolutions without issues. perform a compression test to help you decide if you should go further without pulling the engine. without lifters pumped up, and rings possibly gummed up, compression numbers may not be high, but you will identify any dead holes. if compression numbers are promising, now assume the distributor points need to be cleaned. NEVER run these engines with even a quart of old gas mixed with a full tank of fresh gas. tank should be drained 100% prior to trying to start the engine. old gas turns to glue, and will make the intake valves lock up in the guides and bend your valves (thats probably the most common reason for these engines being pulled and cars being parked.) the pushrod is the weakest part of the valve train, so its the first thing to give.) at this point, pull the oil pan and clean out the inch, plus, of sludge thats potentially plugging the pickup, consisting of lead contamination and deposits from vintage oils, prior to start up. NEVER EVER put any kind of solvents or cleaning detergents in the crank case on any unrestored vintage engine! that includes marvel mystery oil, which is mineral oil and solvent. its literally no different than dumping sand in your engine. also assume the carberator will need to be rebuilt as well as the fuel pump (if not now, later prior to daily driving the vehicle.)
gasoline engines need 5 things to run: fuel, air, spark, compression, and vacuum. the majporit of the time, a non starting issue is going to be either fuel or spark related. (incorrect iginition timing falls into the "spark" catagory.) turn engine over to top dead center, install spark plugs again and distributor with rotor pointed at number 1 (passenger side front), taking note that the distributor housing is installed flush with the block and shaft is engaged in the oil pump. static time the engine by rotating the distributor cap over the rotor, by hand with the ignition on. if theres no spark, then the points art opening, theres a bad ground, or wiring needs to be traced back with a test light. ensure accelerator pump is squirting fuel with the air cleaner off. if not, identify whether the accelerator pump has failed, needle and seat and gummed up from bad gas, fuel pump is bad, or theres restriction/blockage in the fuel line going to the tank.. after establishing that all fluids are topped off, crank and start the engine. dont let it idle excessively at first. dont be afraid to run it for only a short time if you are by yourself, to look the engine over for leaks or overlooked other issues. now set your inititial timing based on 30 degrees total, using a dial back timing light. the limiting bushing has fallen out of these distributors 95% of the time, so if the initial is set by the book, it will over advance.
once the engine's running and you are satisfied with the condition of it, the head gaskets should be changed, as they rust out, allowing the water to shortcut through the block and not cool it, and exhaust valves should be changed as they commonly fall apart and drop with age. now is also a good time to decide or at least consider timing chain replacement as 59 and later engines came with an aluminum/nylon cam sprocket that can fail at any time, resulting in bent valves. whether its original can be checked easily with a magnet through the fuel pump hole in timing cover.