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Onan 4.0 BFA armature maintenance.

chrish001

Registered
I've rebuilt my carburetor and have it running well but decided to tear down the genset for inspection before setting the governor speed. Some of the A/C brushes were stuck and the commutator and slip rings need work. By looking at the photo is cleaning something that I could perform or should I have it done by a shop? I've also posted pics of the bell end and bearing. The bearing is intact but dry so I'm going to have my local auto parts supply cross reference the Nachi number to a Timken or Federal bearing. I plan on sandblasting all of the frame parts and tins for repainting. What is the nominal brush length that can still be used? Replacement Onan brushes are quite expensive.
 

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zuhnc

Subscriber
Last Subscription Date
12/08/2019
Don't forget to save the bearing anti-rotation clip! Visible (barely) in the upper portion of the outer bearing race, third picture. New bearing will require a notch to be cut, as per the old bearing, for the clip to fit and do its job. Yes, the commutator needs turning and mica undercut, and slip rings trued up. Looks like some damage due to high current, with the stuck brushes. Good luck. zuhnc
 

chrish001

Registered
Don't forget to save the bearing anti-rotation clip! Visible (barely) in the upper portion of the outer bearing race, third picture. New bearing will require a notch to be cut, as per the old bearing, for the clip to fit and do its job. Yes, the commutator needs turning and mica undercut, and slip rings trued up. Looks like some damage due to high current, with the stuck brushes. Good luck. zuhnc
I had considered securing the bearing with medium strength Loctite but you don't think that would do the job?
 

chrish001

Registered
My local repair shop quoted @ $120 to service the commutator and slip rings, which is more than I paid for the generator. None of the surfaces are pitted so I may consider attempting it myself. Perhaps some all-thread the same diameter as the through bolt and use my drill press with strips of 1200 grit sandpaper then move to crocus cloth. I'll keep everyone posted on my progress.
 

Vanman

Subscriber
Last Subscription Date
07/10/2019
That looks to me like it needs to be cleaned up on a lathe, ideally. In a pinch, I suppose commutator stones could be used. Won’t be ideal, but may be adequate.

Don’t want to use anything with grit, such as sand paper, as it is my understanding that the pieces of grit can get stuck in the copper, where they remain, making short work of the brushes.

Keith
 

zuhnc

Subscriber
Last Subscription Date
12/08/2019
No thread locker. That bearing has to move laterally to allow for armature lengthwise expansion due to heat. The engine end is fixed by the crankshaft thrust bearing. The crankshaft can expand, also. Thrust bearing clearance accommodates this. With thread locker, one runs the risk of end bell breakage. That is the purpose of the anti-rotation clip in the groove; to allow for that expansion. You could use some high temperature gasket sealer, but I think it would deteriorate over a period of time and allow the bearing outer race to rotate, damaging the end bell. Not easy to fix. If the clip is broken, you can use a piece of spring steel of appropriate size, anneal the ends only, and just bend hooks in it. The middle will still be hard and perform its intended function. A small piece of broken fish tape, from one of your electrician friends, is a good substitute. That armature is heavy. Be careful, and best of luck. Don't forget to undercut the mica after cleaning/dressing. Each copper segment has to be completely isolated from the next. High mica can cause damage to brushes, as well as the commutator segments due to arcing, caused by poor contact. zuhnc
 

chrish001

Registered
I went ahead and bit the bullet and had a local shop service my armature. He initially quoted me $130 but had it done 2 hours later and took $100 under the table. He also resealed all the windings. I found a replacement end-bell bearing at O'Reilly's. I now plan to sandblast both end-bells as they are very corroded. I stopped at my local ABC (Auto Body Color) to have them color match the Onan paint and asked them about a coating for the end-bells. She recommended a self etching epoxy primer after sandblasting. ( of course I'm not going to coat the bearing race!). The next planned step is to sandblast all of the tins and repaint with the matched Onan color, the engine block is next for sandblasting after I seal all of the openings, then install new front and rear crank seals. I'll keep everyone posted with pics of the progress.
 

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Vanman

Subscriber
Last Subscription Date
07/10/2019
Ooh, nice! :D

Just make sure that the auto parts store bearing is of a good quality from a reputable brand. :brows:
 

Eric.S

Registered
I also "reseat" the brushes (new or used) to the diameter, a piece of thin fine waterproof sandpaper 180 degr over the sliprings/comm with the brushes in their holders and springs mounted. Pull the sandpaper a few times back and forwards.

Eric
 

zuhnc

Subscriber
Last Subscription Date
12/08/2019
Very nice job on the armature; looks new! Were you able to recover the bearing clip in one piece? That is the best way to go with the new bearing. Please keep us posted, with pictures. Thanks for those provided so far. zuhnc
 

chrish001

Registered
Very nice job on the armature; looks new! Were you able to recover the bearing clip in one piece? That is the best way to go with the new bearing. Please keep us posted, with pictures. Thanks for those provided so far. zuhnc
I have a 20 ton press and went very slowly.
 

Motorhead

Subscriber
Age
67
Last Subscription Date
07/09/2019
That bell end with the bearing looks pretty rusted and corroded. you want to be real careful removing that bearing so you don't break the bell end. Soak it with penetrant and use some heat around the alloy so the bearing comes out easy. My understanding is that the bearing needs to be able to move back and forth. I maybe wrong so one of the older guys might say different.
 

chrish001

Registered
I've spent the last two days sand blasting and am pretty happy with the results, especially with the stator. I was very careful around the windings and it cleaned up very well as did both bells. The stator will protected with the self etching epoxy primer. All of the tins have been sand blasted and are ready for paint. I'll be doing the engine over the next several days and will post pics of it also.
 

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chrish001

Registered
I heated my garage up to 80° and shot my end bells and rear cover inside and out with epoxy primer today. I'm real happy with the results. All of my tins, intake, coil and carb are painted and just waiting for my gaskets, seals and brushes to arrive. I'm going to remove both front and rear crank flanges so that I can press the old crank seals out and press the new ones in and then install new flange gaskets. I'm getting pretty excited about putting it back together. More pics to follow.
 

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chrish001

Registered
The engine has been sandblasted and awaiting parts before I paint. I've overhauled an air-cooled Corvair engine and understand how critical heat dissipation is. Shiny surfaces dissipate heat less effectively than flat surfaces. I've sandblasted the cylinder and head fins very well to remove all paint and corrosion and also removed any excess flashing. I'm going to coat the cylinder and head fins with high temp flat black paint but the rest of the block will be Onan green. The base plate has been sandblasted and I'm putting on multiple coats of high quality undercoating, not the cheap auto parts spraycan crap. I'm maintaining the baseplate at 90° confirmed with an infrared thermometer for best cure rate.
 

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chrish001

Registered
The engine is painted after sandblasting and the end bell is coated and new bearing with clip installed, quite a difference from the initial pic. I'm flushing the crankcase with diesel to clear out any sand that may have made it past the old seals and then putting on a new Wix filter and filling the crankcase with Rotella.
Why are my photos 90° out of rotation? They are correct in my gallery:shrug:
 

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JohnnyC

Subscriber
Last Subscription Date
07/13/2019
Very nice job! Sandblasting then coated with epoxy primer, it will last for decades.

JohnnyC
New Jersey
 
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