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Rear Generator Bearing Replacement DKD 7.5


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  #1  
Old 07-27-2009, 11:34:33 PM
stratosurfer stratosurfer is offline
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Default Rear Generator Bearing Replacement DKD 7.5

All,
I have a 7.5 DKD diesel Onan that is a 1990 model in my RV. It has right at 1000 hours now and I noticed in the manual that it is calling for a generator rear bearing replacement. I called my service shop in Abilene (authorized Onan repair station) and they said they could do the bearing, but the Onan technician on staff said he had never done one in his career there; no one had had one fail in his 10+ years in a very busy shop. He told me to inspect it and ensure the outer housing isn't spinning.
I understand how critical this bearing is as it's failure trashes the generator. Do I need to do this ASAP? Or monitor the bearing annually.
As well if the bearing looks good should I shoot it w/WD 40 or other spray lube?
Thanks
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  #2  
Old 07-28-2009, 10:11:16 AM
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Dave Edmonds Dave Edmonds is offline
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Default Re: Rear Generator Bearing Replacement DKD 7.5

I stand to be corrected, but I don't think WD-40 would be a proper long-term lubricant for a bearing. I would think some form of grease would be in order. It's just as much work to remove, repack, and reinstall an existing bearing as it would be to install a new one - probably the reason Onan recommends replacement, rather than a simple repacking. If the work is being done by an Onan technician (for money), the cost of the bearing is a small percentage of the total bill. If you do it yourself, the situation is different.
Dave Edmonds
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Old 07-28-2009, 10:57:09 PM
Wayne 440 Wayne 440 is offline
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Default Re: Rear Generator Bearing Replacement DKD 7.5

I have replaced one end bell bearing in all of the generators I have owned. Nonetheless, if it were mine, I would figure Onan recommended 1000 hours for some good reason on that model, and replace it.

Having said that, were it not for the Onan recommendation, I would say buy a spare bearing and keep it handy, since the parts you have spares for will never fail.

(immediately after typing this, I look with relief at my spare RDJC water pump)
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Old 06-24-2011, 08:56:04 AM
NosmoDKD75 NosmoDKD75 is offline
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Default Re: Rear Generator Bearing Replacement DKD 7.5

Wayne440,

I see you have lots of experience changing out Onan bell end bearings and I need to do that in my 7.5DKDFJ. I have the service manual which goes over the steps of taking the generator apart but doesn't state what really needs to be done to just change out the bearing.

I hope I can just remove the bell end, pull the bearing off and "press" the new one back on. Is that OK or should I take it all part and check it out completely? I have just over 2000 hours on it, its a 1995 year make and I am the second owner. I doubt any service at this level has been done so I know I want to do it soonest...

Any inputs would be greatly appreciated.

Steve
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Old 06-24-2011, 09:17:38 AM
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J. McNugget J. McNugget is offline
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Default Re: Rear Generator Bearing Replacement DKD 7.5

Here is the directions for changing the bearing in the HDKAG genset - I believe it superceded the DKD.

Generator Bearing:
Inspect the bearing for evidence of outer case rotation
every 1000 hours of use. The bearing should
be replaced every five years, because the bearing
grease gradually deteriorates due to oxidation.
Replace the O-ring if it shows evidence of wear or
deterioration. Renew grease if necessary (moly
only).

Rotor Bearing Replacement
1. Clean the bearing and shaft mating surfaces.
2. Apply Loctite #680 adhesive to the shaft mating
surface.
3. Apply Loctite #747 activator to the bearing mating
surface.
4. Install the bearing and allow ten minutes curing
time before handling the assembly.

I'd suggest that you follow the Loctite directions, because a loose bearing will send you to the machine shop, if you are lucky.

John
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Old 06-24-2011, 09:39:54 AM
David C David C is offline
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Default Re: Rear Generator Bearing Replacement DKD 7.5

As long as you have some mechanical skills, the bearing replacement should not be a problem. When you "press" the new one on, just don't put any pressure (hit) the outer race. If you do not buy the bearing from Onan, STAY AWAY from any "no name" bearing, unless you want to be changing it every 250 hours instead. If you use a NTN or Nachi bearing, you should get the same service life as you did with the original one. When I used to rebuild alternators and starters, I saw MANY rebuilt units that that had bearing failures. I mostly used NTN brand and I don't rememeber having to apologize to a customer for a failed bearing during the warranty period or out of the warranty period.

David C.
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Old 06-24-2011, 11:31:24 AM
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Billy J Shafer Billy J Shafer is offline
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Default Re: Rear Generator Bearing Replacement DKD 7.5

Don;t know who your Onan tech is. But I have had many fail over the years. Easy to replace just follow the instructions McNugget posted. Remove the bearing and take it to a bearing shop. They can match it for you. I agree with the NTN bearings. Good quality bearings.


I have relatives not far from you. Down in Roosevelt Texas. My grandmother was a teacher in Brady years ago.
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Old 06-25-2011, 05:57:46 PM
bbuchorn bbuchorn is offline
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Default Re: Rear Generator Bearing Replacement DKD 7.5

Just my 2 cents worth.
What I do, is check and repack the bearing once a year. If you can see the end bell bearing like i can on my NHE 6.5 . just take a sharp pick and carefully pop out the oil seal ring on the side of the bearing, wash and blow out the old grease then repack with a good moly grease. then snap the seal ring back in. Most bearing failures are caused by "sealed" bearings going dry anyway.. Lots easier than pulling one down to begin with.
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Old 06-26-2011, 07:35:55 AM
NosmoDKD75 NosmoDKD75 is offline
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Default Re: Rear Generator Bearing Replacement DKD 7.5

Thanks for that needed info. One more question, can I just take off the bell housing, pull the bearing and install as you stated WITHOUT any rotor support? Basically, in vehicle work without any wires to undo and reattach (etc.) is what I am hoping for.

---------- Post added at 07:35 AM ---------- Previous post was at 07:31 AM ----------

David C. thanks. I got an Onan bearing. Its box states a Feb 2011 'build' date so it hasn't sat on a shelf for very long. I will look into the NTN bearings.
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Old 06-26-2011, 08:07:12 AM
Arkie Arkie is offline
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Default Re: Rear Generator Bearing Replacement DKD 7.5

Quote:
Originally Posted by bbuchorn View Post
Just my 2 cents worth.
What I do, is check and repack the bearing once a year. If you can see the end bell bearing like i can on my NHE 6.5 . just take a sharp pick and carefully pop out the oil seal ring on the side of the bearing, wash and blow out the old grease then repack with a good moly grease. then snap the seal ring back in. Most bearing failures are caused by "sealed" bearings going dry anyway.. Lots easier than pulling one down to begin with.
I re-pack bearings the same when I know they just need re-packed and the roller, needles, or races are not rough. Sometimes I have to remove a bearing to remove the old grease and then check the bearing dry to see if it's smooth. I've carefully used silcone sealant on the removed side seal for a good dust seal to the internals. Just be careful and not get silcone sealant inside. Silcone (sand) may ruin a bearing if it's gets mixed with the grease inside. (silcone sealant is not a recommended lube for high speed bearings)
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