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Beogram 4002 DC motor bearing oil infusion

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Krolroger
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Krolroger posted on Sun, Dec 10 2017 10:52 PM

I was inspired by Beolover's video to have a go at re-infusing with oil the oilite bearings on a slightly screechy DC motor.

Disassembly was straightforward, but it became obvious that there are various versions of this motor.  This one is marked MHN-5P2RDS and has a date stamp of July 1975.

The most obvious impediment to removing the bottom bearing in the manner that Rudy demonstrates (though the top one came out fine) is the fact that the base plate that carries the brushes is epoxied to the feedback coils and the metal enclosure so there is no possibility of prying it up to remove the bottom bearing.

I therefore had to consider immersing in oil as much of the bottom enclosure as necessary in order to get oil into the bearing - having first unsoldered the pcb underneath.

I used a jam jar with a vacuum wine stopper glued into the lid and pulled a vacuum with a Vacuvin pump.

After 24 hours, I removed the base plate and let the excess oil (10w40) drain off overnight.  I gave it a quick once over with contact cleaner. 

I found it easiest to insert the rotor into the bottom bearing by putting the two nylon washers in place first and then separating the brushes with a toothpick to allow the commutator to slip through.

Using a toothpick through the top bearing, I held the armature in place while I lowered the casing onto it.

Torqueing the screws correctly is important or the motor won't run.  I found that I could adequately secure the top bearing retaining tags by means of a cork underneath and some thin nosed pliers.

The motor runs silently drawing 19mA at 5v.

 


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Krolroger
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Quite bubbly top bearing ..


Dillen
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Dillen replied on Mon, Dec 11 2017 6:27 AM

Nice work.

But you really need to use oil with the right additives.

Originally SAE30 was used and that will of course be fine, though I do find the modern version(s) a little tough running in some motors, perhaps
the viscosity is a little too high.

I like to use Mobil Velocite 6, so far it has not let me down.

 

If you remove the remains of the old and dry oil (24h acetone bath, stirred every now and then) before adding fresh, it would be an even better and
longer lasting result.

 

Martin

Krolroger
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Thanks, Martin,

Will try that on the next one.

Craig
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Craig replied on Mon, Dec 11 2017 5:05 PM

Just out of interest, I'm not currently contemplating carrying out this activity, how much vacuum is required to perform the infusion? Is there a minimum for a longer period? Or is it simply a given negative pressure that must be attained before the air will start to be leeched out? 

Dillen
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Dillen replied on Mon, Dec 11 2017 9:15 PM

It's not a lot, really.
The more of the old and dry oil you can get out of the material the easier will it be to suck air out.
It's when the vacuum is released again, that the fresh oil draws into the material because of the vacuum that has built up in there.

Martin

whiteman
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I agree with all that Martin suggests.  I did my first oil infusion surgery on my 4002 this last weekend.  Fortunately for me, I have access to a very powerful vacuum chamber at work that can pull down to 0.003 mbars.  I put my bearings in that chamber and it took about an hour and a half to complete, which was about an hour longer than I thought it would take.  The higher the vacuum, the faster it goes.

And while I'm here, a comment on bearing installation.  When I put my motor back together the armature did not turn as freely by hand.  I had read about screw tightness on the shell making a difference, but honestly that should not be the controlling factor.  The bearings can "swivel" to make alignment with the motor shaft.  This does not guarantee that the bearings are in perfect alignment after assembly.  They are held tight enough in the housing that they can easily be held a little out of axis to the shaft and cause extra friction (pulling more amps).  Re-tightening the 3 shell screws will make small adjustments to the bearing alignment but it is purely hit-and-miss.  My solution was to hold the motor in one hand and sharply rap its side against my alternate palm... or against a surface like a running shoe sole.  Firm, but not too hard to break anything.  Rap it a couple times on its side and then rotate on axis several degrees and rap again.  After doing this several times turn the shaft by hand and see if it runs more freely.  In my case it was a dramatic improvement and turned much easier than before I took the motor apart.  The rapping "slams" the shaft against the bearing inner surfaces and forces the bearings into perfect alignment.  If you don't do this the motor will most likely pull excessive current and that is not good on the motor or electronics.  Do not depend on the bearings to wear in over time as that will only cause damage.

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