Fred8
The engine only sounds quiet because my system is designed to run at 1150 rpm.
If I ran it at 2600 rpm with full output it gets very loud. (Typical Changfa type engine.)
The pulleys are sized so that the generator spins at synchronous 3600 rpm when the engine is turning at 1150.
This limits the system to 1.3 kw max output at 120 volt AC.
To modify the engine for an external oil filter you will have to confirm that your engine A] Has an oil pump and forced lube system. B] The engine has a removable filter screen that can be modified.
I don't have pictures available of the modification, but the the objective is to remove the cover giving access to the pressurized screen filter chamber.
Remove the screen filter and machine a plug that fits into the filter chamber. The plug has holes and an o-ring which re-route the incoming oil to an external port. Through the filter, and back into the screen chamber, then onward into the engine. Each engine size probably has a different sized screen and chamber so each mod is custom to the owner.
As far as I know, only engines size 175 and larger have the removable screen cover. Smaller units (160,165, 170) do not have this feature.
Your assumption of approx. 1/3...1/3...1/3 power between crankshaft, coolant, and exhaust energy is correct.
Gathering exhaust heat however, can be messy and difficult. Soot and carbon clog exhaust heat exchangers very quickly if not designed correctly and if exhaust velocity is not sufficient. Even then, regular cleaning may be needed.
Here is another example of an enclosed system that a fellow built. Provides power and heat.
https://www.youtube.com/watch?v=Rx0ODuaoWwEgood luck with your project, keep us posted
cheers veggie