[ARC5] BC-348 Backlash Suggestions

[John Hutchins]

Dave -
First you will have to remove the entire tuning assembly.
Somehow mark the worm gear and the shaft mating location.
Use a file to dress up the boogered pin ends.

I agree never hammer these pins out.  Press them out.
Find a machine shop that has a small press or make an  C clamp into a 
press or cruse harbor freight for one.
Hutch


On 4/24/2013 9:23 AM, David Stinson wrote:
> Been reviving a BC-348 for a friend.   It had a "doofuss-try" I hadn't 
> seen before- someone rotated the bandswitches 180 degrees.  Didn't 
> know you could even do that.
>
> After this and lots of other work, it's playing well
> and is one of the best sounding 348s I've ever done. Even the crystal 
> filter works well.
> One common problem remains- tuning backlash.
>
> The three major contributors to backlash in a 348 are the tuning 
> capacitor gear, the worm wheel and
> the worm shaft.  Here is a photo:
>
> http://home.netcom.com/~arc5/348gears.jpg
>
> First, make sure all the gears are clean and lubed.
> Put some drops of GOOD penetrating oil on the edges of each gear and 
> let them sit.
> Do this until the two halves of the gears move freely.   You can test 
> this with a small
> screwdriver inserted between two edge teeth.
> Mesh the teeth and they should spring back.
>
> The gear on the end of the cap is not too tough
> and that's good, since it's usually the big baddie.
> Just takes patience and practice.  Close the cap all the way and make 
> sure this coincides with the end
> stop on the tuning knob.  Loosen the two screws on
> the gear end, but don't remove them.  You want to be able to disengage 
> the gear from the pinion, but just barely.
> This is best done at a 45-degree angle toward the front.
> I use a pair of hemostats to engage both sides of the gear and 
> well-compress the spring.  Then, making sure the tuning knob is still 
> on the stop and the capacitor is still fully meshed, re-engage the 
> gear and tighten the cap back down.
>
> The parts where I could use suggestions.
> The worm gear wheel also needs to be retensioned, but the assembly is 
> pinned together and the ends of the pins "boogered-up" so you can't 
> drive them out
> without damaging the whole assembly.
>
> I can't disengage the worm gear wheel to retension it like the cap 
> gear, nor can I remove the worm gear shaft, as it is also pinned.
> In the past, I've used hemostats to removed one of the worm wheel 
> springs, stretch it out, try to put it back, cursed at the 27th try, 
> then watched the spring "sproing-ing-ing" off into oblivion,
> found another spring in the junkbox, stretched it too much so that, 
> once I did get it on,
> it stuck -out the sides of the gear etc. etc.
>
> And then there's the worm gear shaft- this problem is nasty and is 
> also common on later production 348s.   The worm shaft slops "in and 
> out" towards the back and front.
> Common symptom is "wibble-wobble" while tuning
> that is most pronouced on the higher bands.
> The shaft has a wimpy leaf spring under the worm
> and a felt pad under the tuning knob that help some,
> but it's no cure.
> I cannot remove the worm to add a washer or bearings
> under it.  Only someone with an advanced machine shop should attempt 
> it since you will absolutely wreck the thing if you try to hammer and 
> whack the pins out.
> So I'm looking for suggestions on how to address
> the slop in these two gears.
>
> How about a couple of snap-rings under the worm shaft?
>
> TNX ES 73 DE Dave AB5S
>
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