Onan Marquis 7000 Generator Starter Revs But No Action

With the spark plugs removed, it should roll smoothly through every revolution. If the plugs are still IN, then you're feeling the cylinders coming up on their compression strokes and that's normal.
Try what PackPack suggests. Pull the plugs and check to see that it rolls smoothly. Then install Starter and try to Start it. Starter should engage and genset should rotate smoothly. Then roll it again by hand. There shouldn't be any resistance from the Starter. You'll know the starter's releasing and there's no interference.
It could be the genset happened to be shut down with a piston exactly at Dead Center. Where it stops going Up and hasn't started going Down. If the genset than sat that way a long time, the piston could have gotten sticky in that position. They're much harder to crank than when piston happened is part way.

That sounds good. You may have to set the valves. But for right now pull both spark plugs out and then try to start it. It won't start but see if it will spin the motor . That will tell us about the valves. Are you sure your getting the full 12 volts to the starter when you are trying to start it.

I did have the cover off at one point and was spinning the blower wheel and it wasn't spinning that freely. It had very difficult places throughout a revolution that required some effort to push through. How easily should it spin? I do have the manual as downloaded from the link in the previous post. Thanks for all the help so far.

I'm calling the blower wheel the flywheel I'm sorry. Once you take you top cover off you can turn the blower wheel by hand or put a socket on the bolt . Then we will know if the piston is stuck or the valves are stuck or need adjusting you may also check your bearing on the other end may need some oil or grease in it. Do you have the parts manual ?

After a few times putting the new starter in and out of the genny and then confirming it works on a bench test we concluded the starter is engaging but not able to turn the flywheel. When I try to turn the flywheel with my fingers inside the starter hole it is very difficult to spin in the direction the starter is trying to move it. You can't access the flywheel with the top cover off from what I can tell. Is a rebuild or a new generator the next step?

Thanks. I'll check that. Is there any trick to the grounding. The manual shows a tray bolt as a ground but I don't see any wires that look like a ground to a tray bolt.

There are two tiers to the housing just take the top one off and make some full revolutions of the flywheel. Also with a multimeter check your volts when you engage the starter you could have a dirty connection on the start soileniod or battery. Check all your connections from the battery all the way to the starter when you push your start switch.

Installed a new starter and it's not moving the flywheel. There is just a lower sounding buzz noise with not engine engagement. I tried it with the engine running too. I was able to reach my fingers into where the starter goes in and move the flywheel. It turns but it is not exactly easy to turn. I'm unclear on what you are suggesting Kpack. Any recommendations from here?

The top part of the housing may have to come off I can't remember. Or the wire mesh from the bottom by the muffler. If its to hard to turn the valves may need setting so the top has to come off anyway. If its real hard to turn pull both spark plugs out and the turn it to see how hard it is if its easy to turn with the plugs out you will have to set the valves to spec. I took my gen out its to hard to work on in the trailer.

I got the starter off today and gears are all stripped off. It was a bit difficult to take off. I took out the first 3 of 4 bolts on each side of the tray and swung the generator down so I could get in behind it more easily. Unscrewed both bolts on the starter but it still wouldn't budge. After a lot of hammering and prying with a flathead screwdriver (which resulted in breaking of one of the bolt flanges) nothing was happening. Some WD-40 and wedging a wrench between the engine bock and starter allowed me to pry it to the side and it popped off finally. Because of the broken part on the starter housing, I'm going to replace the whole starter which is $157 from the Onan dealer. I'll try putting that in tomorrow and see what happens.

What is the best way to see if the engine flywheel is turning properly? I don't see a way to access it to turn it by hand so I can make sure the starter won't break again. Thanks for all of the help so far in helping me find that problem.