Re: buying a used yanmar 2qm15, TIPS?
Congratulations on your dadship. Nothing better.
I have two 2QM15s...owned one since '83 and the other I bought in '07 as a garage queen spare parts engine since the age of the QMs means some parts are hard to come by.
When I bought a salvaged boat in '10 that needed an engine I restored the garage queen for the second boat rather than invest in a new one.
The failures I have had are in the cooling and exhaust systems. I had to have an exhaust manifold soldered due to a crack (no new ones available). I had to replace exhaust elbows on both. I had to rebuild a worn out water pump. I had to have an alternator rebuilt. I had to replace the injection pump on one engine but that was my fault because I let it sit idle for too long and it got a little rust on it where clearances were important. Exhaust elbows are available but the only sources of some major parts like the manifold or water pump are to fabricate them or find one on a salvageable engine that is still serviceable.
Mine have been good engines for the 4-5 ton boats I have pushed with them. They sip fuel while cruising at about 2100RPM - about a pint and a half an hour at five knots or so in relatively calm conditions.
Look for cracking in the exhaust elbow. Also the raw water cooled manifold will plug with exhaust/salt/metal deposits and may require cleaning using muriatic acid and a relatively long stiff prod to work on the hard deposits. If hoses haven't been replaced in some time you will likely need to replace them. Check to see if zincs still have active material to determine if they have been routinely replaced...if so the corrosion will probably be limited. The engine does have decompression levers.
These engines were built in the mid seventies (almost 40 years old!!) so when I saw parts becoming limited several years ago I bought parts and gaskets needed for most repairs except pistons/rings/cylinders. All the gaskets and hoses were available then but seem to be getting harder to find. You will certainly need the gaskets for pulling and replacing the exhaust manifold and elbow.
When I bought the garage queen engine it had been removed from a boat due to overheating and a head gasket leaking water into the engine room. I brought it home and built wooden rails for the mounts and hooked up cooling water and a battery and primed the fuel system using a portable tank and squeeze bulb. It started after a couple of revolutions. If the engine you are looking at has no known problems you should be able to do the same. If not...you should be very skeptical about its condition.
I got the engine for 400USD and put about 800USD into reconditioning it not including engine controls and cables/new motor mounts/electric panel and wiring/muffler/exhaust hose/bronze exhaust fittings. These support systems cost almost about another 1200USD. I did most of the installation including engine beds so was able to keep the cost down but you have to understand the support systems are VERY expensive...especially exhaust hose and fittings and motor mounts.
Talk to the folks at West by North (or see their website) about a Campbell Sailer prop for the engine/boat combo you have. They can hook you up...for another 500 or so.
"It's not what you know that's important...it's what you do with what you know." -H.G. Rickover