[ARC5] Power up Modulators

[Mike Hanz]

I don't know where I got the wildly misplaced reputation of being a 
perfectionist, but those who know me well understand that the truth is 
/far/ from that..heh, heh.   I wrote the article in ER to try and cover 
the gamut of dynamotor bearing resuscitation, from a few drops of oil to 
complete replacement.  That way an individual could make his own 
decisions.  There is a broad spectrum of enthusiasts on this list, from 
those like Robert, Dave, and myself who tend toward the "try it, you'll 
like it" approach, to those who want everything pristine, with original 
bearings that work to original specs.  That's sort of a challenge in 
trying to cover a subject like this.  Robert's posit below covers 90% of 
the bearings - you generally need to pull them only if you replace 
them.  For that remaining 10% of cases where the OP is 'thrifty' like 
me, a good puller will generally allow you to pull the bearing and use a 
decent greasing tool.  That's the classic way of greasing a bearing, and 
it works well for the normal dynamotor bearings one finds in this 
hobby.  The observation about brinnelling is a concern /if/ the shaft to 
bearing fit is RC3 or tighter  (not generally the case with dyno 
shafts), the particular bearing steel isn't hardened to the degree that 
usual post-1940 bearing steels exhibit (common with mainland Chinese 
replacements I've tried), or the shaft has a great deal of corrosion on 
it (in which case the bearing is usually toast as well.)  Gordon White's 
ARC tool works well with new armature shafts and new bearings that don't 
measure up to vibration/noise specs, but the clearance between the end 
of the commutator and the back of the bearing is only .024" on the DM-32 
size dynos, and only .032" on the larger DM-33 frame, which means that a 
puller like that often bends in the removal process and may damage the 
soft commutator segments (don't ask me how I know...)  If the tool 
works, then a couple of jeweler's screwdrivers would probably work just 
as well.  I've had them simply slide off into my hand at times, so the 
fit isn't very tight for most of them.  See the bottom of  
http://aafradio.org/garajmahal/TBX-2arm.html for one puller I made for a 
worst case scenario - it works the same as Gordon's example but has more 
meat on it to allow greater pulling forces with a larger three jaw 
puller.  With bearings still running less than $5 each, it's often 
easier to just pull it and install a new one rather than worrying about 
it (...if you're the worrying sort.) 

Another strategy is Dave's, which is to slap some grease in it and see 
how it works (my preference as well, quite frankly.)  If it starts 
making noise, so what?   :-)   I have an old Craftsman version of a 
Rotabroach (high speed hand grinder) that I have used for four decades.  
Its bearings protest sonically from time to time, so much so that I long 
ago purchased new ones from Sears to install, but in some arcane 
reversal of Murphy's law, the bearings refuse to give up.  Lately it has 
been sounding like a new tool - it must be afraid that I'll be tempted 
to do drastic surgery on it...  It's probably the same syndrome that 
becomes manifest when you buy a spare fan belt and thermostat for your 
new car - you will never need them even if you keep the car for 15 
years...  So it is with dynamotor bearings.  They may protest from time 
to time, and growl uncomfortably for hours on end, but with decent 
lubrication they will continue to operate for an amazing amount of 
time.  It all depends on your personal level of background noise pain.

The critical parameter is bearing race temperature, and in the military 
dynos, the bearing end play can affect that in a big way.  I usually 
fiddle with the shim pack on the end bearing cap , tightening and 
loosening the two cap screws until the sound is minimized, then adding 
or removing shims until I can get the same sound with the screws drawn 
tight.  Less or more end clearance will almost always begin to heat up 
the bearing housing above ambient, sometimes dramatically.  What appears 
to happen is a certain amount of ball oscillation, even in bearings that 
have no particular spec for preload.  There is a way to do this with 
precision measurement equipment, but it's a pain to do and ideally you 
need extremely accurate dimension measuring tools and a granite surface 
plate...not worth it IMO.  My time is worth less than the measurement 
tools needed.

73 DE KC4TOS

WA5CAB at cs.com wrote:

>The only reason for buying  a bearing puller (and the small ones are not high dollar items) would be to use to remove an old bearing for disposal and replacement with a new one. 
>
>But 99% of them install up so closely to the end of the commutator(s) or winding core that the only thing you can grab onto in order to remove them is the outer race.  When you pull on the outer race in order to remove a properly 
>fitted bearing from the armature, you (usually) damage the outer and inner races and possibly the balls due to "brinelling".  I.e., you put dents in the races and flats on the balls.
>