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Onan Generators

Onan 7NHMFA26105D, been sitting a while...


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  #1  
Old 06-14-2017, 02:08:41 AM
PnishrPW PnishrPW is offline
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Default Onan 7NHMFA26105D, been sitting a while...

Newest refugee - came in an RV we bought recently. Shows 47 hrs on the clock, blipped the starter and it turns over. PO doesn't remember last time it was used. Plan is to pull the unit and go through it. Only thing I see wrong at the moment is a broken exhaust hanger and flange bolt.

I downloaded all the manuals, picking through them now. I figure the carb and slip rings will need attention minimally. Probably going to be a minute before I get to work on it, I'm still in the middle of my MDJE project.
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  #2  
Old 06-14-2017, 12:48:15 PM
len k len k is offline
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Default Re: 7NHMFA26105D, been sitting awhile...

Since been sitting , clean the slip rings before making AC or reg dies.

Nice thing about this gen is it will run even if it's not making AC, so you can unplug the reg and let engine run to easily clean slip rings. I ground sides off a kitchen fork and use that to hold scotchbrite pad under the slip rings while running. Very easy way to clean them in about 3-4 seconds this way.
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Old 06-16-2017, 02:44:10 AM
PnishrPW PnishrPW is offline
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Default Re: 7NHMFA26105D, been sitting awhile...

Well, another rainy day over here on the green side... But nice and dry under the RV! Crawled under the gen and had a lookie at it. Nothing new jumped out at me, found the reg and unplugged it. It was a bit grumpy but it fired. Ran like crap for a few but got a bit better - carb definitely needs some love. Shut it down, checked resistance - was a couple ohms over spec. Decided to go for it, plugged the reg in and fired it up. It makes power! Surging a bit, but smoothes some with time. Went in and turned the breakers on, fired one A/C waited a few minutes and then fired the other A/C too. Carried both, surging a fair bit so I shut the A/Cs off then shut the gen off. Next step is to pull it out completely. Won't start from inside but will stop, probably something stupid.

Thinking real hard about sticking one of my spare 6.5NH spec D's in and selling the NHM after I go through it. It only has 48 hrs on it, it ran when pulled - it should be worth $3000+ on Epay right??...
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Old 06-16-2017, 12:12:54 PM
len k len k is offline
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Default Re: 7NHMFA26105D, been sitting awhile...

I'ld clean slip rings anyways. After cleaning them and letting them sit either 3 or 6 months ( I forget) they developed a high resistance spot right under where brushes sat, and ~ 1/3 to 1/2 that resistance everywhere else. If let it sit another ~ 3 months you get a 2-nd high ohm spot , so eventually you can deveop many high ohm spots. Running ~ 45-60 minutes only lowers ohms ~ 10-20% ( genhead was not energized).

I like the small box package shape of the NHM for house backup. Like that it has an internal muffler for small footprint. Also it has a rectangular cover over 2/3 of genset, so if have outage during sleet/snow storm you can just quickly lay a sheet of ply wood on top as a roof to keep it dry. Can't do that with NH or NHE.
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Old 06-16-2017, 03:01:31 PM
PnishrPW PnishrPW is offline
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Default Re: 7NHMFA26105D, been sitting awhile...

Yeah, I'll be cleaning the rings when I pull it for service. I should've measured before I ran it, oh well...
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Old 09-09-2017, 01:51:18 AM
PnishrPW PnishrPW is offline
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Default Re: Onan 7NHMFA26105D, been sitting a while...

Got some time to work on the RV today, unplugged the reg and fired it up - man was it finicky... Went ahead and replaced the trashed exhaust hangar and flange bolts that have been bugging me. Took a bit to light but finally came to life. Needed a couple of tries to stay running, warmed it up and changed oil/filter (went with the longer filter). Still surging a wee bit but better than last run. Checked slip ring resistance - actually in spec. I forgot to check when I started, left a note on it to check next time though. Plugged reg in and restarted, carried both ACs fine, ran them 1-2 mins then shut them down. Surging was slightly less under load but still present. Plugged in the remote switch but would only stop, not start - same as before. Minor issue for another day. Still going to pull it for service sometime, carb needs some love. I've already picked up plugs/air & fuel filters, thinking about plug wires. Need to grab a carb/manifold gasket, just so I don't need it...

I used my Fluke 39 power quality meter to check it out, was a little suprised... Output looked a bit dirty, until I unplugged the Magnatek battery charger then it cleaned up nicely. Apparently its got some pf and harmonics issues, not horrible though. Same result on utility power, doesn't seem to bother anything though. Volts: 124 unloaded, 123 with ACs running. Very little grunt on gen when ACs started (not at same time). Micro made it grunt some, still not bad though.

Do these prime with stop? If it's supposed to it ain't. Not much issue to add a run/off/(prime) switch, would be handy. Pulled the fuel pump fuse and ran it sans reg until carb was empty. Still haven't hit 50hrs yet, maybe next time I run it.

I'm still twitchy about all the electronics on this thing, would rather have "dumb" NH I think.
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Old 09-09-2017, 07:52:55 AM
KPack KPack is offline
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Default Re: Onan 7NHMFA26105D, been sitting a while...

I don't think it will prime. I sold one the other day on cl for 900.00. You never know.
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Old 09-09-2017, 10:18:35 AM
len k len k is offline
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Default Re: Onan 7NHMFA26105D, been sitting a while...

No prime on them.

If add a prime I'ld make it a spring loaded switch, so you can't forget and leave it on.

Mine surged so bad it really didn't run without help. In carb dip tube into bowel there are 2 long jet tubes with 8 cross holes each. Clean them both, one is hiding behind screw in cap. Mine were VERY plugged, as was main jet adjust.

I didn't clean my idle mix jet and it ran great. I had brass screw in caps on top labled M+S short jet tubes under them were about as clean as they were from factory. I guess stuff up there is not wetted by liquid gasoline when engine is off and don't get plugged.
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Old 09-09-2017, 12:44:04 PM
len k len k is offline
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Default Re: Onan 7NHMFA26105D, been sitting a while...

Correction.... While I didn't take my idle jet apart to clean it, I did however blow it in both directions with compressed air. I also blew the ~ 4 tiny .010 inch dia ports in carb throat. I just used a steel tipped blow gun with 150 psi air on all the ports and passageways. On another carb I only had 30 psi air, it worked perfect too.
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Old 09-10-2017, 11:59:36 AM
JT240Z JT240Z is offline
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Default Re: Onan 7NHMFA26105D, been sitting a while...

Do yourself a favor and get those slip rings cleaned up properly. I've lost a voltage regulator just because of not doing my regular 30 day exercising the genset and then running it under full load. Ended up being a $300 mistake. Cleaning the slip rings is a piece of cake if you can get to the cover plate. On my RV, you have to drop the genset to get to anything so when it's out I do everything. I just use a scotch bright pad. Usually, pull the plugs (good to inspect them anyway) and crank it over with the plugs out while pressing the pad against the rings. Cleans them in a few seconds.

I'd also go through the carb even if it is running. Not that complex of a device and you'd be amazed at what a difference a clean carb can make.

Quote:
Originally Posted by KPack View Post
I don't think it will prime. I sold one the other day on cl for 900.00. You never know.
Electric pump primes pretty quick even if the carb is empty so I wouldn't even add a prime feature. Just bought a backup Marquis 6500 LP for $1150. The unit had around 50 hours on it and was never installed in an RV. Was used to backup an AC system in an outside work building and was always housed inside. Thing looks like it's brand new. I've seen these very same generators go for upwards of $2800 on eBay. Just the luck of the draw on what they can bring in. The 7000's do much better than the 5000's. Mine was actually wired to 240V when I got it. The PO did the stator wire swap so it could run the AC system. I returned it to the original parallel configuration for max 120V current capability. Love these generators.
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Old 09-10-2017, 12:06:16 PM
len k len k is offline
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Default Re: Onan 7NHMFA26105D, been sitting a while...

Nice thing about BGM/NHM models is all specs but A will run even if it's not making AC.

I'm lazy so I unplug AC voltage reg, and let engine run to do the work cleaning slip rings. I ground 2 side tines off a 4 tine metal kitchen fork, jabbed strip of scotchbrite on end, tied other end and briefly held it UNDER slip rings. Problem solved and quick.

Could add a switch to disable flashing to pin 7 of reg during cranking, that will stop gen from starting to make AC. That way don't have to unplug reg to protect it.
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Old 09-10-2017, 03:54:22 PM
JT240Z JT240Z is offline
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Default Re: Onan 7NHMFA26105D, been sitting a while...

Quote:
Originally Posted by len k View Post
Nice thing about BGM/NHM models is all specs but A will run even if it's not making AC.

I'm lazy so I unplug AC voltage reg, and let engine run to do the work cleaning slip rings. I ground 2 side tines off a 4 tine metal kitchen fork, jabbed strip of scotchbrite on end, tied other end and briefly held it UNDER slip rings. Problem solved and quick.

Could add a switch to disable flashing to pin 7 of reg during cranking, that will stop gen from starting to make AC. That way don't have to unplug reg to protect it.
I usually just take out the two screws that hold the brush block in, remove the block and crank the engine without plugs in it. Gives me better access to the slip rings. No need to unplug the voltage reg and lets me see what condition the plugs are in.
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Old 09-10-2017, 04:06:28 PM
len k len k is offline
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Default Re: Onan 7NHMFA26105D, been sitting a while...

Brush holder 2 screws have plastic "caulk" over them to keep water from pooling and rusting screws in. I'ld at least use antiseize on them.

Don't let brush wires short to ground or you'll likely be replacing the AC voltage reg $230-330
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