Onan 2800 S2 Disable But Still Stops

[nomadikus]

Pretty much the title. I've disabled what I think is S2 but the gennie only runs while I'm holding down the start button. Off the top of my head these things are happening and possibly related?

1. I have no load attached. Should run anyway, right?
2. The oil dipstick is close to full (measured the right way, ie not screwing it in) and I've read various opinions about where it should be. Is there a "too much oil" failsafe? I'm using 5W30 but I don't think that should really matter at an ambient temp of 70F.
3. I don't have my air filter in for testing purposes but I can't imagine that is very important in the very short term.

This is a short video from my test run with S2 disconnected. Any insights welcome! Anyone who has pulled out their gennie and has it on the bench might be interested to see where I attached to ground. Attempts in other places (specifically on the case, where the paint is insulative) didn't have it turning over at all - a good ground connection is vital (as has been said elsewhere in this group).

https://drive.google.com/file/d/17GNicuxvCwKVoZreRRYeMh3lfOlIT6LZ/view?usp=sharing

 

[booster]

Pretty much the title. I've disabled what I think is S2 but the gennie only runs while I'm holding down the start button. Off the top of my head these things are happening and possibly related?

1. I have no load attached. Should run anyway, right?
2. The oil dipstick is close to full (measured the right way, ie not screwing it in) and I've read various opinions about where it should be. Is there a "too much oil" failsafe? I'm using 5W30 but I don't think that should really matter at an ambient temp of 70F.
3. I don't have my air filter in for testing purposes but I can't imagine that is very important in the very short term.

This is a short video from my test run with S2 disconnected. Any insights welcome! Anyone who has pulled out their gennie and has it on the bench might be interested to see where I attached to ground. Attempts in other places (specifically on the case, where the paint is insulative) didn't have it turning over at all - a good ground connection is vital (as has been said elsewhere in this group).

https://drive.google.com/file/d/17GNicuxvCwKVoZreRRYeMh3lfOlIT6LZ/view?usp=sharing

Have you checked to see if you have 110v output while running with the start button pushed. I think Onan bypasses the ignition and fuel pump and runs it directly when on the start button and then switches them to the output from the generator once the button is released. If you have 110v with the button pushed, then you may have an issue with the control board, I think.

 

[nomadikus]

Checking Output Voltage

I haven't checked output voltage, no. I was reviewing the FlightSystems troubleshooting guide it says it needs the Low Oil Level sensor open and pin P2-4 "ungrounded". Pin P2-4 is the Magneto Kill, I guess. I'm out of my element on it but I think that if oil level is low it closes a circuit to ground, which grounds Magneto Kill, which kills running. I'll check to see if I have 110/120V on the output wires next as I haven't figured out how to test from the control board.

Have you checked to see if you have 110v output while running with the start button pushed. I think Onan bypasses the ignition and fuel pump and runs it directly when on the start button and then switches them to the output from the generator once the button is released. If you have 110v with the button pushed, then you may have an issue with the control board, I think.

 

[nomadikus]

Tried to check the voltage but didn't see any. Pulled the control board cover off to inspect and didn't see any obvious problems but then realized my 110V breaker showed 'off'. Thought it should be on so I switched it. My lithium starter needed to be recharged so I switched a small new 12V battery. It tried to turn over once and now... just the starter spinning. AND the hub/fan assembly. But it doesn't seem to want to turn over at all (like I can hear the starter spinning but I don't hear any fire in the hole). I'm guessing either the battery I got was too small (but I think then the hub assembly / fan wouldn't spin) or... I created some new problem. There was a loud backfire prior to this happening but I think it was on par with backfires earlier. Ugh.

 

[nomadikus]

I keep making things worse...

So somehow, amidst a backfire or two, something may have gone seriously wrong. Now when pressing start I get the starter motor revving up, solenoid driving engagement to flywheel and flywheel spin (you can see this in the video).... and nothing like a crank at all. This doesn't sound like a fouled plug (which I just replaced), and it doesn't even sound like running dry of fuel (which I did previously). Did I actually just break the crank itself somehow? And if so, what can cause that to happen? The audio here will probably tell somebody something...

https://drive.google.com/file/d/17j0-I2IMF0qya2s3_Vhteshodu8uNnzj/view?usp=sharing

 

[booster]

So somehow, amidst a backfire or two, something may have gone seriously wrong. Now when pressing start I get the starter motor revving up, solenoid driving engagement to flywheel and flywheel spin (you can see this in the video).... and nothing like a crank at all. This doesn't sound like a fouled plug (which I just replaced), and it doesn't even sound like running dry of fuel (which I did previously). Did I actually just break the crank itself somehow? And if so, what can cause that to happen? The audio here will probably tell somebody something...

https://drive.google.com/file/d/17j0-I2IMF0qya2s3_Vhteshodu8uNnzj/view?usp=sharing

I don't have an Onan engine exploded parts diagram, but on many small engines the crankshaft is connected to the flywheel by a woodroof keyway and key that is made to shear if something goes wrong. They are commonly sheared by big backfires so that kind of makes sense that could be what is wrong. It is also common that they will partially shear before the spin completely free and when they do it often messes up the ignition timing so they won't start or they run very poorly. I have fixed a couple of lawn mowers that did that.

 

[DaveBad]

Fault Codes

I just came across this. It may help give you some more info.


https://thecampingadvisor.com/onan-generator-fault-codes/

 

[nomadikus]

I just came across this. It may help give you some more info.


https://thecampingadvisor.com/onan-generator-fault-codes/

Thanks! I don't see any lights on the 2800 but I'll check again.

 

[nomadikus]

I don't have an Onan engine exploded parts diagram, but on many small engines the crankshaft is connected to the flywheel by a woodroof keyway and key that is made to shear if something goes wrong. They are commonly sheared by big backfires so that kind of makes sense that could be what is wrong. It is also common that they will partially shear before the spin completely free and when they do it often messes up the ignition timing so they won't start or they run very poorly. I have fixed a couple of lawn mowers that did that.

Oh, wow, that really could be it. It was quite a backfire. I have every manual I could find downloaded - now that I know that exists I can try to find it. I'll report back whatever I find! Thanks for the help.

 

[nomadikus]

Oh, wow, that really could be it. It was quite a backfire. I have every manual I could find downloaded - now that I know that exists I can try to find it. I'll report back whatever I find! Thanks for the help.

I thought I could possibly see the key but it looks like it's behind the fan. On 'start' the fuel pump engages immediately (and there is fuel), there is spark (as tested by holding the plug next to the case, the flywheel spins based on the starter motor engaging and some ac is generated (not much but it's only 1-3 seconds of spin). I'm pretty sure I've disconnected the low oil level sensor so that can't be it. I admit that I'm a noob at this but it seems like it has to be compression and probably the key? If anyone has any other ideas please let me know but I guess that's going to be next!

 

[booster]

In most engines the starter turns the flywheel so if the key there is broken the piston won't be moving or the crankshaft.


Is the magneto on the flywheel end or the other end, probably with the fan over it? If it is on under the fan it is also pretty likely the fan might have a key holding it in index that has sheared. If the crankshaft is turning, look in the spark plug hole for piston movement, the flywheel key is likely OK. If the crankshaft is moving and fan isn't, look at the fan key.

 

[nomadikus]

Just from reading the manual I think the magneto is on the flywheel end. I wish I'd waited to read your comment about watching the piston move through the spark plug hole but at this point I've pulled off the intake baffle, disconnected all the wiring, hot, pulled that big capacitor, etc. Actually, now that I'm thinking about it, I think I can spin the flywheel myself and see if I have piston movement. In any case I think my next step is to get the housing around the fan off so I can visually inspect the key. I'll check for piston movement first though, thanks for the idea!

With Intake Baffle Removed (next is removing that black plastic housing):
https://drive.google.com/file/d/1oPfL2aPhnUdBKBwNPoW3IsY5kThYeQCj/view?usp=sharing

Intake Baffle + Fuel Assembly put to the side
https://drive.google.com/file/d/1mZQKFzGBs1KGG_T1l6vlgQzodl2YiSrr/view?usp=sharing

EDIT: It looks like spinning the flywheel is moving the piston. Maybe a partial shear would explain it? I'm not certain. I have an endoscope so I just took 30 seconds of video while I rotated the flywheel here. At this point I'm far enough in that pulling the housing and taking a look seems like the next step.

https://drive.google.com/file/d/17peC1IDRDtgomDmlRvO9RLfRlhGEt2WQ/view?usp=sharing

In most engines the starter turns the flywheel so if the key there is broken the piston won't be moving or the crankshaft.


Is the magneto on the flywheel end or the other end, probably with the fan over it? If it is on under the fan it is also pretty likely the fan might have a key holding it in index that has sheared. If the crankshaft is turning, look in the spark plug hole for piston movement, the flywheel key is likely OK. If the crankshaft is moving and fan isn't, look at the fan key.

 

[nomadikus]

Oh, wow, that really could be it. It was quite a backfire. I have every manual I could find downloaded - now that I know that exists I can try to find it. I'll report back whatever I find! Thanks for the help.

Actually if I'd looked at the diagram I'd know it would have to be only a partial shear if any - I do get fractional AC voltage on the outputs just from the starter motor spinning + engaging for a few seconds, so I think that suggests that most of the generator portion remains intact.

I did have the muffler disconnected, which includes the "spark arrestor". I wonder if not having that connected was what caused a major backfire or internal damage.

 

[nomadikus]

In most engines the starter turns the flywheel so if the key there is broken the piston won't be moving or the crankshaft.


Is the magneto on the flywheel end or the other end, probably with the fan over it? If it is on under the fan it is also pretty likely the fan might have a key holding it in index that has sheared. If the crankshaft is turning, look in the spark plug hole for piston movement, the flywheel key is likely OK. If the crankshaft is moving and fan isn't, look at the fan key.

The fan spins when the starter does, so that is engaging. And when I spin the fan by hand I do see piston movement in the spark plug hole. A mystery for now I guess.. at least I'm getting an education on these things!

 

[nomadikus]

Summary Update

Findings so far are:

1. Disabling the S2 sensor did not appear to change run characteristics. Everything runs until I stop pressing 'start'.
2. A large backfire occurred while testing, after which I don't appear to get any real crank action. I do hear the starter spin and I can see the flywheel spinning as well.
3. Pulled the fuel line off the carb to observe the pump working - seems fine.
4. Observed piston movement via the spark plug hole suggesting it is not a sheared key.
5. Spark plug is new + I can see a spark when it's pulled and close to ground (the case) on ignition, so the whole ignition system is energized appropriately.
6. Just running the starter starts to generate a voltage so that eliminates the entire generator and the ac wiring as a problem (I think).

Just a progress report for those interested. Thinking now that the big backfire bent a valve or it's stuck open for some reason. A compression test is next.

 

[booster]

I think I have been misunderstanding what you have been explaining some of the time. In the last post you said the flywheel turns but the engine doesn't crank?


What are you referring to when you say "crank". Around here that means the engine is turning OK on the starter, which you may be calling "spinning". Are you using "crank" to indicate the the engine is actually firing the cylinder(s)? If so that is a big difference.


With my definition of "crank" if the flywheel spins and the engine isn't "cranking" it would mean only the flywheel is turning, but your definition seems to indicate the is also turning but that the engine is also. That is a big difference as the my understanding would point to a broken flywheel key, and yours to lack of spark, fuel, a timing issue, or even a dropped rocker arm or bent valve or pushrod.


So the lack of firing (or crank if you wish) could very possibly be internal. If it is a bent valve you probably would feel it kiss the piston as it turns over but not always. We have heard of Onans that have dropped rocker arms before so that would probably be most likely. That is easy to check by pulling the rocker cover off in most engines.

 

[nomadikus]

Yeah, I think I was confused about the term, but when I originally wrote that I hadn't taken note that the flywheel was spinning and I hadn't checked for piston movement (because I'd forgotten one could do that). My mistake on terms. Once I went back in to the diagrams and looked at what was connected where (based on you mentioning the flywheel key) I think just having spark + piston movement narrowed things down a lot further. I'm being verbose just so the next guy gets as much context as he can but if I'm using the wrong terms that would be confusing - thanks for correcting my misuse.

My next step is to reassemble the intake baffle + connections, do a compression test and next take off the rocker cover and probably the head (depending on what I see with rocker cover removal). I'm new to this so (can't believe it took me so long to get into - pretty fun taking these things apart) I'm picking up a lot just from feedback on this post (and the other onan 2800 post that has been active lately).

I think I have been misunderstanding what you have been explaining some of the time. In the last post you said the flywheel turns but the engine doesn't crank?

What are you referring to when you say "crank". Around here that means the engine is turning OK on the starter, which you may be calling "spinning". Are you using "crank" to indicate the the engine is actually firing the cylinder(s)? If so that is a big difference.


With my definition of "crank" if the flywheel spins and the engine isn't "cranking" it would mean only the flywheel is turning, but your definition seems to indicate the is also turning but that the engine is also. That is a big difference as the my understanding would point to a broken flywheel key, and yours to lack of spark, fuel, a timing issue, or even a dropped rocker arm or bent valve or pushrod.


So the lack of firing (or crank if you wish) could very possibly be internal. If it is a bent valve you probably would feel it kiss the piston as it turns over but not always. We have heard of Onans that have dropped rocker arms before so that would probably be most likely. That is easy to check by pulling the rocker cover off in most engines.

 

[nomadikus]

So just as a test I reconnected S2, didn't help. Put the intake baffle back on and used starter fluid, just in case something went wrong somehow with the carb, no dice. We took off the rocker cover and you're right, both rockers were dropped and the rods were somewhat bent (which is what allowed them to drop, I guess). Bent those back (and will order some new ones) but still no luck, and when we checked the rods again (just in case they were bending easily now) they were still pretty straight.

We also tried to spin the flywheel by hand (far harder to do with rods and rocker arms properly seated, but doable) and after a few full rotations didn't observe any movement of the rods. I've got a friend helping now and I think we're going to take the head off and see what we see.

So the lack of firing (or crank if you wish) could very possibly be internal. If it is a bent valve you probably would feel it kiss the piston as it turns over but not always. We have heard of Onans that have dropped rocker arms before so that would probably be most likely. That is easy to check by pulling the rocker cover off in most engines.

 

[booster]

I hope you will be able to find the parts, as Onan totally dropped all ongoing support for the non inverter style (new) 2800 generators. The engine was a Robin Subaru and was discontinued by Subaru (Fuji Industries I think) and Onan was the only user of it so no other stock but Onan, I would suspect. Numerous users were told by Onan when in for repairs that the engine parts were not available so it could be that way.


If you can get parts, I would get the pushrods and and both rockers plus a head gasket as getting a look at that hand the valve heads would probably be a good idea.


Can you push the valve down by hand without them sticking? Only push on the valve stem because if you push on the spring retainer sometime the keepers will pop out and the valve will drop into the cylinder.

 

[nomadikus]

So far the parts have been available on the Onan site (rods and valves). I don't trust myself with the engine internals yet so I'm waiting for a friend to come by and check things out with me. He did say that the rocker arm seemed like it had more play than it should, and the rods seemed to fall out kind of easily, even after we straightened them. I did just do a compression test and I'm only seeing 32 psi as it cranks (from the starter motor attempting ignition), so it looks like we're probably opening it up to see what's going on.

Oh, and I can push both valves using their respective rocker arms. There's a lot of resistance from the spring but they do both move.

I hope you will be able to find the parts, as Onan totally dropped all ongoing support for the non inverter style (new) 2800 generators. The engine was a Robin Subaru and was discontinued by Subaru (Fuji Industries I think) and Onan was the only user of it so no other stock but Onan, I would suspect. Numerous users were told by Onan when in for repairs that the engine parts were not available so it could be that way.


If you can get parts, I would get the pushrods and and both rockers plus a head gasket as getting a look at that hand the valve heads would probably be a good idea.


Can you push the valve down by hand without them sticking? Only push on the valve stem because if you push on the spring retainer sometime the keepers will pop out and the valve will drop into the cylinder.