Quote:
Originally Posted by bestclimb
Someone would have to be pretty brain dead to not understand what the engine is telling you long before you can do any damage. I can do the same thing <20mph in 5th in most cars.
Not so much. A marine engine is built to run at a higher power setting for long durations. As in 80% load at 3500 rpm. They use heavier duty bearings, better internal oiling, and increased cooling to deal with the higher internal temperatures and higher average stresses that they are submitted to continuously.
The bogging and chugging you get when you lug an engine is due to the spark happening before top dead center, and with lower speed the piston is not far enough past top dead center when the pressure of the expanding fuel charge is increasing. So instead of adding a push down the burning fuel charge puts a stopping pressure on the piston and the momentum of the engine and previous combustion in other cylinders forces the "lugged" cylinder over the top and down.
This increase in resistance coupled with low oil pressure (because the engine driven oil pump is not turning very fast) causes the rod bearings to squish all the oil out and the bearing surfaces come into contact.
A marine engine with better bearings can withstand this for longer (though it would not likely be subjected to this as water is a viscous medium to transmit power to rather than a tire/road interface) but it is still bad for it.
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right , plus a marine engine you can never get it to lug or bog down as there no direct drive as you in water there always slippage or whatever you want to call it being propeller powered ,engine never gets loaded down at low speeds .
The problem is with small engine if you gear it to high (low final drive) is it just don't have the torque in low rpm to be geared like that . You would get a condition were you be at HW speeds and not allow you to be in high gear until a higher speed for best FE .