While rated variously at 42HP, 47HP, 50HP, etc., this engine is overrated. It's a small engine, despite it's bulk and weight, and should be rated down around 30-35HP in actual use.
I contacted Perkins
in the UK with my serial
and model number for the 4-108.
They e-mailed all the details including the HP rating.
For my engine it was 51 HP.
That being said, the 51HP is measured at 4000 RPM
which is more like "war power" but the max continues recommended by the factory is 3000 RPM.
The HP at the reduced RPM would obviously be less.
On a few occasions I have had to use full power and the old diesel will deliver, but slowly overheating
occasions when I dialed in 4000 RPM would be when bridges was about to close on me (too late to stop) and to avoid collsions.
At max power it will make big noise
with boat speed at 7 knots or more, foam flying, smoke blowing and in general it feels like the engine is coming apart.
(My ship is 33 feet with a 25' water line)
I have also ran a 42' Jouet Ketch
with the same engine and that boat was faster with less RPM..Probably the much longer waterline.
As for the leaks
I have a small/slow leak at the aft seal. It seems to stop whenever the boat is used every day.
Just sittin for months, then running it will spit some oil, but not much at all anymore.
It was worse just after bought the boat 8 years ago.
I have never attempted to tighten things up or try to "fix" it...No room back there.
Using an oil absorbing blanket under the engine and in general it stays white for 100 hours between oil changes. Except when rarely run, then the blaket goes gray, then black.
Have overhauled the cooling
system and done other routine maintenance
. Still overheats slowly but surely whenever I run at 2600 RPM or above for more than a few minuttes.
Don't think I am over-propped as the 4000 RPM can be reached if needed.
Also boiled out the heat exchanger
and swapped with the spare one back and forth.
Have a hunch my intake may be too small.
Not a big problem, getting my 5.3 knots at 2100 RPM, 5.6 at 2400 an 5.9 @ 2600...Pretty much all I need to do.
Found 2100 RPM to be the best power setting for lowest fuel consumption
and best speed..It also agrees best with the hull
and everyting else. (No black mustache on the transom from soot)
Fuel consumtion @ 2100 RPM is right at 0.6 gallon per hour.
Tried with a taller prop, got much more speed, but the GPH went up to 1.0. Probably overloaded the engine as well.
Have 2 props and have had both repitched and balanced to find the best combo, think I have it now....
Love my 28 year old 4-108, hope she will last another 28.