RPM and life of engine are not necessarely connected, a long stroke, slow turning engine can have as much wear as a high rpm short stroke engine. its the piston speed that matters among many things. for the same rpm a piston with a 6" stroke has to travel 3 times as fast as one with a 2" stroke for the same rpm. , and when its time to change direction the stresses on mechanical parts
are much greater on a long stroke engine... so, a 1500 rpm engine might last less than a 3000 rpm engine..
no one mentionned kubota diesels. the V2203, 48 hp at 2800 rpm will easily last 20,000 hrs, they are used in reefer units for semi trucks, carrier corporation recommends oil change
intervals of 2000 hrs with normal oil
and 4000 hrs with synthetics. recommended rebuild
is 20,000 hrs, they run their engines at 1600 rpm, about 3o hp. beta marine
and nanni both use that engine. kubota also makes many smaller diesels, i have a gen set with a small 3 cylinder kubota that has 12,000 hrs. oversize the engine, run it at a lower rpm closer to the torque curve and it will last forever and get better fuel
efficiency. dont prop it for max rpm, prop it to be matching its load or about 75% .. years ago i had a 75ft schooner, 84,000lbs , it had a ford 120 diesel
i spun a 29" prop , at 1400 rpm i would get 1.4 gph at 6 knots 24 hrs a day. theres great diesels today, 30 years ago we serviced Whitte diesels on remote
farms, slow turning and heavy, single
and twins, they ran 24hrs a day for 3 years, we didnt even shut them off to change oil
, pulled the drain plug
let it drain and refill.....the little 2cylinder 21 hp diesel
i removed from my boat weight over 500 lbs, my new 48 hp weights 500 lbs and is smoother and doesnt vibrate the boat... progress can be a good thing.