+1 for cobbadog
it seems to me that "if" one were wanting to tear down the engine for overhaul, you would be removing the generator head anyway
so what harm would be to eliminate the head as a possible cause of the problem?
been giving this thing more "thunking" and i recall over the years some really expensive problems relating to similar problems
1. back in the late 80's while working in seattle, we had a used IH 4070B cabover in the shop because of low power and excess smoke
the diagnostics lead the foreman to conclude that it needed a new turbo, so it got a new turbo
when that didn't work, they put in a set of injectors,
when that didn't work they did an inframe overhaul,
when that didn't work, the condemned the transmission, and exchanged it
when that didn't work they removed the front and rear differentials, and of course found nothing
i came to work for the company after all this had been done, and was tasked to find the problem
the first thing i did was ask to talk to the former owner, i asked him how it ran for him
"well, uh it ran fine up to 3 years ago when we parked it!"
ok... hmmm i wonder
i took down the air cleaner stack and found a huge birds nest clogging the bonnet, and of course it clogged off a huge portion of the air needed to run properly, removed the nest and waalaaa... back to full power!
lesson learned
2. i got a call from one of my customers with a p30 stepvan, with a chevy 350 early throttle body
the truck started fine on a monday morning, ran 30 miles without issue, and up restarting after his first stop
it couldn't make 15 mph, and even at that it took about a 1/4 mile to get to 15mph
i removed the dog house engine cover and started the engine, and notice that when i pushed down on the gas pedal
the intake flex house seemed to move just a bit, i removed the hose from the aircleaner and started up again, this time pushing the pedal to the floor, and that is when i saw the top cover suck down so that the wing nut was about 1/4" loose..hmmm
took a look up into the snout,and saw what appeared to be an extension spring, maybe 3/8" diameter, thinking it was something to do with the thermo door, i grabbed ahold and gave it a yank.... "HoLy Crap!"
out came the biggest rat i ever saw! he apparently crawled up from the flex hose to the air cleaner snout and when the driver started the engine he got sucked up to the thermo door and then made a 30 mile trip which sucked all the juice out of him... but he effectively jambed the door and the intake so there was little air flow available for the engine.
lesson learned? A. never ever overlook the simplest of possibilities, and B. bring a change of undershorts because you never know what you might have on the other end of whatever you pull on.
the point is this, over 40 plus years of twisting wrenches i have seen a lot of crazy stuff, and i have seen mucho dollars spent trying to correct a 50 cent problem.
digression
two other examples of what i am talking about
a kenworth boom truck with a 400 big cam cummins, runs with good power, little to no smoke, not problems, until you come in off the road and shut it down and try to restart in 15 or 20 minutes, then if you do it will turn the whole world blue, smoke everywhere, massive engine knocking, and oil coming out of the expansion joints of the exhaust manifold... and i mean running out and looking/feeling like engine oil.
cummins shops, they sent it in to two for two different opinions, both quoted near the same for a major overhaul
problem ended up being a 3 dollar fuel tank vent, which plugged and built up pressure, cummins injectors being cam actuated and pressure time type will continue to dribble or nearly spray fuel into the cylinders if there is pressure in the tank... so fuel continued to be issued to the cylinders and when the engine started of course it is near hydro locked, and fuel that is chared looks just like engine oil.
3 dollar vent and the company was saved a $22k dollar overhaul bill
i found this problem twice in the 90's and cummins sold one engine overhaul and when that didn't fix it they would not stand behind the
problem and try to make it right with the customer.
another example
another boom/crane truck,
the crane when placing roof trusses on the plate line would swing slowly then without warning sweep at a vastly faster rate, knocking off framers, which if they are on a second story get really grouchy.
the company had it in to 3 hydraulic crane/boom shops in the seattle olympia area, spent $55k dollars and still no fix
turned out to be a pressure gauge that measured lift and sweep pressures and had a double check valve in it do that it could read
for one function or the other, not both.
the gauge was broken, cost was about 200 bucks, so one of the shops at some point connected the two lines together and removed the gauge, "who needs a stinking gauge anyways?"
it took me about 2 weeks of spare time research to determine that "if" you connect both of those 1/4" lines together you connect two pilot valves, one for lift one for sweep together, the result is the pilot for sweep senses the higher pressure from the lift circuit and increases the pressure and flow to the sweep valve and away to the races you go
bottom line, before you tear things all apart, spend all the time needed to eliminate all the cheap and easy possibilities, unless you have a lot of spare time and money to expend.
fwiw
bob g