No expert but sure looks like I have a crack in my cylinder wall here? I was also wondering since I'm so scared of buying a engine on offerup/craigslist or the like and it having problems would a good compression test on all cylinders rule out any problems with the engine? Is it possible for all the cylinders to have good compression but there still be some hidden problem with the engine? Does a engine need oil for it to be safe to do a compression test and will not having oil in it throw the compression reading off? Sorry about the 50 questions, thanks in advance.
hard to say what's going on with that cylinder...usually, cracks in cast iron have a jagged look to them. A compression test will tell you if an engine is bad, but it won't rule out other problems. Usually a compression test is meaningful if you run the engine first, then do the test. It's usually not a good idea to turn an engine over much, if it doesn't have any oil in it. If you're worried about buying a used engine, then don't pay more than core value for it, and expect to have to rebuilt it, and maybe replace lots of parts. If you need ***urance, then buy a new engine, with a warranty. Good luck
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