I have a Onan 4ky generator on my RV, I had to replace the rotor because the last one self destructed. I installed a new one inspected and vaccumed the entire generator tray and checked the clearance to the stator everything looked great. I reinstalled the generator and ran it with the AC on for the load. It ran great for exactly one hour and then shut down. I removed the cover and noticed pieces of plastic and a small piece of copper wire in the tray. I removed the generator again and found the new rotor was destroyed. It appears the winding breaks loose from the rotor shaft where it is glued, moves out breaking the plastic winding frames. The plastic then gets caught in the stator breaking the windings. Has anyone else see or heard of this issue ??? These rotors are $500 bucks, i think the supplier is going to replace it under warranty but I need to know what is causing this, defective rotor ??Poor design ??

Just a wild guess from someone who has no knowledge of THAT particular generator, but could it be that the winding gets too hot? Perhaps air vents are clogged or something??? I was part of the engineering team at a company that rewound large motors and generators many decades ago, and so I do know a little about the materials used in generators in general, and heat is what kills most of them, either high heat for a short period, or low heat for longer periods. That this one failed that way suggests the adhesive/plastic may have overheated.BTW, this query has nothing to do with the Forum. I'll notify a moderator and ask it be moved to a more appropriate forum, where better answers might be forthcoming.

This is an interesting situation. Is sounds like you installed the new rotor correctly and, if it ran for an hour there's probably nothing the windings are contacting that would cause it to fail.I would question the supplier and/or Onan to see if this is a common problem. Hopefully they have the answer.Maybe, you just got a faulty replacement rotor?(I think naturist has an idea of what's causing your problem, forget my response. :))

We're supposed to "exercise" our gensets monthly by running half an hour or more under load. Everybody thinks of keeping the fuel system from gumming up. That's true and very important, but that long run, under load, is also to drive moisture out of the windings. You've replaced the rotating coil. What's the condition of the other coil, the stationary one? I wonder if it's "swollen" from moisture and once it warms up, drags on the rotating coil and damages it.

The ONAN "4KY" series is a very popular 4-KW genset. Compact, light weight, 3600-RPM, single cylinder.

Onan 4ky Generator | Good Sam Community

naturist
Nomad
Feb 03, 2016
Just a wild guess from someone who has no knowledge of THAT particular generator, but could it be that the winding gets too hot? Perhaps air vents are clogged or something??? I was part of the engineering team at a company that rewound large motors and generators many decades ago, and so I do know a little about the materials used in generators in general, and heat is what kills most of them, either high heat for a short period, or low heat for longer periods. That this one failed that way suggests the adhesive/plastic may have overheated.

BTW, this query has nothing to do with the Forum. I'll notify a moderator and ask it be moved to a more appropriate forum, where better answers might be forthcoming.
gbopp
Explorer
Feb 03, 2016
This is an interesting situation. Is sounds like you installed the new rotor correctly and, if it ran for an hour there's probably nothing the windings are contacting that would cause it to fail.

I would question the supplier and/or Onan to see if this is a common problem. Hopefully they have the answer.
Maybe, you just got a faulty replacement rotor?

(I think naturist has an idea of what's causing your problem, forget my response. :))
j-d
Explorer II
Feb 03, 2016
We're supposed to "exercise" our gensets monthly by running half an hour or more under load. Everybody thinks of keeping the fuel system from gumming up. That's true and very important, but that long run, under load, is also to drive moisture out of the windings. You've replaced the rotating coil. What's the condition of the other coil, the stationary one? I wonder if it's "swollen" from moisture and once it warms up, drags on the rotating coil and damages it.
2oldman
Explorer II
Feb 03, 2016
I think you mean kw, not ky.
j-d
Explorer II
Feb 03, 2016
The ONAN "4KY" series is a very popular 4-KW genset. Compact, light weight, 3600-RPM, single cylinder.
2oldman
Explorer II
Feb 03, 2016
j-d wrote:
The ONAN "4KY" series is a very popular 4-KW genset. Compact, light weight, 3600-RPM, single cylinder.
Very good. I stand corrected.
Nucman55
Explorer
Mar 02, 2016
After 3 weeks the supplier is sending me a new rotor, but the fact remains this is the second rotor that has self destructed. So now I am afraid to run it again after i install the new rotor coming until I can find some answers. I find it very funny that Cummins agreed to send a new rotor no questions asked and didn't request that i return the old one
j-d
Explorer II
Mar 02, 2016
While it's apart, can you see if the rotor was hitting the stationary windings/laminations? Rubbed spots? Is there an alignment process? I haven't worked on one of these. Are you consulting a manual?
MEXICOWANDERER
Explorer
Mar 02, 2016
I rebuild these things and the best I could do is guesswork.

You need -professional- guidance from a repair facility that specializes in Onan. The end result is too much work, too much money and too much hassle to experiment with.

I, myself, would phone several huge repair facilities and ask their advice about the Onan rotor. If they and others report a problem, then you need to sit back a moment and make a decision.

If the selected repair facilities all go "Huh?" you will take an entirely different tack.

But that's just me...

Forum Discussion

Onan 4ky Generator

About Technical Issues

Related Content

Onan Generator

Onan Generator

Onan generators

Onan Generator Heat

Onan generator 5500