[ARC5] BC-348 DYNAMOTOR

[J Forster]

WA5CAB at cs.com wrote:

> John,
>
> I think you may have replied to a couple of the posts off-list but I still
> don't know whether it's the brush caps or the brushes that are stuck.  Both
> happen.

Yes, I exchanged several off-list messages. It appears the caps are stuck and can't be
unscrewed. I presume the brushes are either stuck in the holder or are worn out, I
don't know which.

> If the former, another possibility to add to Mike's holder list is a
> scissors type tube puller with the plastic covering over the curved tips.  Hold
> the tube puller in one hand (left for most people) and grab the cap with it.
> Grab the outside of the puller tips with pliers and loosen the cap.

In a later email, it became clear that the brush caps are screw plug type, rather than
pipe cap type. That makes grabbing them by the OD impossible.  8=((

> If the brushes are stuck in the holders, don't pull very hard on the outer
> end of the spring or you will pull the wire out of the brush.  If pulling on the
> spring doesn't remove the brush, you can try pushing on top and bottom sides
> with a flat wood stick but I've never had much success with that.  Unless you
> have new brushes or are sure the ones there are nearly new length, I wouldn't
> recommend trying to get something sharp like a knife blade between the brush
> end and the commutator.

Agreed.

> Assuming you can rotate the armature (brushes aren't stuck to commutators),
> remove the leads from the brush holder terminals.  Remove the two screws or
> studs holding the cast aluminum bearing and brush holder carriers to the field
> coil assembly (steel cylinder).  Pull one carrier away from the field housing
> far enough that you can move the carrier from side to side.  Then grasp the
> bearing end and wobble or rock the carrier back and forth slightly in the plane of
> the brushes while pulling it away from the rest of the dynamotor.  Once one
> is clear of the dynamotor, pull the armature out the open end.  You can then
> get at the commutator end of the brushes with the wood stick and push them into
> the brush holder slightly.  At that point, you should be able to remove the
> brush by pulling gently on the spring.  If it is still stuck, cut a piece of the
> stick short enough to fit between the two brushes.  Grab it with long nose
> pliers and use it to push the brush out.

I'd be really reluctant to pull the machine apart as you suggest. The bearings often
have preload springs and getting them back correctly is distinctly non-trivial. Also,
differing torques on the bolts holding the parts together can impact the shims. If the
preload on the bearings is too much, it will damage them.

On some machines the brush holders are held in with set screws. If those screws are
loosened, you may be able to pull the holders out radially and get access that way.
You need to watch out for the connecting wires though.

FWIW,
-John

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