Well, I would certainly “try to do a compression test”…Pretty simple to just hot wire the starter with jumper cables….
First, look at the engine ID core plug, this number should match the serial number on the transom bracket. A six digit number and/or the letters “RPH” means the powerhead has been replaced with a new one at some point. Not a bad thing. Look for signs over overheating, the white color on the head and exhaust cover will look pinkish or burned if overheated. Look for melted wiring harness’ wear it contacts the block. Look at all the gaskets, and the flange where the two halves of the crankcase mates together. All new gaskets, sloppy/incorrect gasket sealants, ooze/sealer coming from where the crankcase halves mate up could spell trouble. I am always wary of “rebuilt powerheads”. These engines are not hard to tear down and reassemble, but few ever get the fine details right. Piston skirt to cylinder fit has to be right on these engines or they will be hard to start and won’t idle, no matter what a compression gage says.
Look at the gearcase, is the skeg bent/busted? If so, there may be internal gearcase damage also, especially if a stainless prop was used. Spin the prop while watching the end of the prop shaft in an effort to see if the prop shaft is bent. Ask the owner if you can just “crack the lower lube screw open” for a second. The lube should be relatively clean, maybe a little black crud laying in the bottom. Milky gear lube, or raw water spells trouble.
I’m assuming this is a fresh water engine, so corrosion shouldn’t be an issue. You can “hot wire” the trim unit to see if it works, simply jump the battery to the blue and green terminals, then swap them around to change pump direction (up and down). Look for fluid leaks. This engine needs two electrical harness’, one for the control box, the other has a junction box with relays for the trim unit.
Like you say, this is a gamble, cuz you can’t run it on a boat prior to purchase. Ask the owner why the engine has been sitting around. Perhaps the boat just hasn’t been used, or maybe the engine was replaced cuz it wasn’t working correctly. Do whatever you can to minimize the risk, what is the asking price for the engine?
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