Onan 4000 swap

Many of these kinds of jobs require two able-bodied knowledgeable guys.

Thanks for all the reply. Waaaayyy too much work. I thought it would be easier.

A generator or RV repair place might charge some $600 to remove the two units including installing and reconnecting the "good" generator and testing the operation. Installing new fuel filter, hoses, etc. if needed would cost extra.

I had to lower mine to replace the starter motor. It was a similar setup to what you're describing, a cage/frame that attaches to the generator and is hung onto the RV framework. The generator is unbolted and lowered from below. The framework on mine had the bottom portion (where the generator proper mounted) attached to the verticals with eight bolts, two at each corner, which made dismantling things straightforward.

Aside from clearance under the RV, the actual lowering and raising wasn't too terribly difficult with an automotive floor jack. A transmission jack would have been even more convenient, but one uses what tools one has available. (I wasn't clever enough to check the clearance beforehand, which meant I ended up changing the starter with the generator sitting directly below its mount and the outer cover wedged up in the mounting cage...not the most convenient, but easier than raising it up again to drive the RV onto ramps!)

Whatever you do, before doing anything, Check, recheck, double check, & double recheck, try to think at least 2 steps ahead, ie; if I do this what will happen, if I do that, will it work, if I have it on a jack (of any type), will I also have to raise the MH, It would certainly help if you can find an installation manual.Have lots of band-aids available for your fingers. :(
GOOD LUCK

Drew, you're right, it's all in the Details. I added a big heavy BFA genset to a coach that didn't have one before. Compartment had a floor in it and BFA was designed to use a floor. I had two helpers and we slid the 250-pound machine in from the side. Other than to get the generator lined up on the opening, a jack was no help.

Our present 4KY sets in a frame, and the access door is a hole in the side wall. This means ours would have to have the frame dismantled, then genset lowered, and height of genset + jack would require raising the coach.

I've seen some setups where there was no wall below the access door and genset was hung from its top/sides. That one would be easy...

It's not difficult in the conceptual sense. It is somewhat laborious. Certainly with a little experience in hooking up and unhooking, and appropriate tools, it could be done in a few hours...but if you haven't dropped a generator before, it might take somewhat longer.

Unless they've changed things on your particular revision of the 4KY compared to mine (I assume this is a 4KY), it's necessary to remove the starter solenoid, voltage regulator/control modules, and switch panel on the generator to detach the gas line and the AC power output connections. Once those are all detached, it's fairly straightforward in concept to use e.g. an automotive floor jack to support the generator when removing the bolts from whatever sort of mount/subframe is used in the installation, and then drop it down in a controlled manner. Installation is, of course, more or less just reversing the process. (There are also connections to any remote start panel etc. and for chassis grounding; those are readily accessible.)

Do measure carefully to make sure you have enough clearance underneath the skirting of the two generator bays to clear the generator when it's on whatever jack or dolly or whatever you're moving it on. If not, you will need to put the vehicles up on jack stands or ramps or something before starting out.

I think the label on my generator listed it as somewhere around 175 pounds. It's enough that a jack or whatever is very nearly needed to safely manipulate it, particularly in the close quarters of a typical generator bay.

I'd guess Yes, and much easier if you have the two coaches parked on pavement, maybe with genset bays facing each other, and ideally some kind of lifting ginny like a transmission or motorcycle jack. Or two strong helpers. Weight's not much over 150 but it isn't easy to juggle that much weight into a tight space.