I'm a newb to the hobby and working on a Halicrafters S-107. Previous threads here:

viewtopic.php?f=6&t=183098

viewtopic.php?f=6&t=189013


The tuner is apart for cleaning and lubrication. Wow, wish there was a manual for that! It was very sluggish. I'm about to start putting it back together.

As you no doubt noticed in the pic above (sorry for the crappy pic) one of the springs is missing. I cannot tell what, if anything, these springs are supposed to do. I can't say if it was there or not when I started disassembly, but I was not aware of any parts going "sproing!" so my inclination is that it was not.

How important is this part? Is there any way to find a suitable replacement? What is the downside to not replacing it?

Thanks for the support and advice all... you've been a tremendous help to me so far.

For now I wouldn't sweat it. This is a double gear with springs holding tension between this set and the one it meshes with. Purpose of the double gear is anti backlash. It takes play out of tuning which is especially good for short wave. A single spring will do the job until you find an extra.

Make sure that you rotate one of the springs one tooth relative to the other (in the direction that compresses the spring) when you seat it against the pinion gear. This is what will create a tight fit that will eliminate backlash. Otherwise the spring(s) will not perform their function.

Bob

Bob,

I would love to follow your suggestion... but I didn't understand one word. Can you rephrase in a way that a newb can understand, such as step by step?

Also, can anyone explain how this "prevents backlash"? For all I can see, it sits statically in the gear between two pegs, not doing anything. It seems like a uselessly added-in part.

Thanks.

Try twisting the gears one tooth towards the way the spring compresses. This is how tension is place on the gear tooth. It creates a binding or friction on it. so, it stays where you have it set, when it is in mesh with the gear it is driving.

Is it a split gear - two gears tightly together?

I meant to say rotate one of the gears rather than a spring. Oops. Glasdave explained it well.

Bob

It looks like there are wear marks on the backs of one of the wheels that is turned by the dial string.

I'm guessing that the spring rubs there? I've been tinkering with gizmos for a few decades, and haven't encountered that sort of thing before, which is why I'm puzzling over it now.

If you guys say it's not a necessary part then Ok I'm game.

If I wanted a replacement spring though, just for the sake of completeness, how/where would I get one?

And during the reassembly, should I put a little smear of light grease on the wheel where the rubbing occurs?

If you have a jar of springs scavenged over the years like most of us, you can use a section of a compression spring that fits and is approximately the same guage and and "strength." Wear safety goggles when cutting springs. The're nastier than they look.

Of course if you have a watch/clock shop (any more of these?) they would have one. 25 cent item.

A tiny drop of WD40 applied with a toothpick will be appreciated by the mechanism.

A lot of hardware stores carry a selection of springs. You can ind them in the section that has all of the little drawers of nuts, bolts and other hardware odds and ends.

Imagine two ordinary gears meshing. Unless they are very precision gears, there is some play between them: one gear has to turn a tiny fraction of a degree before the engaged teeth turn the other gear. This results in "slop" or lost motion between the gears called backlash. This may not be important for some uses, but in radio tuning it can make for frustration when trying to tune in a station.

In order to avoid this lost motion, you have an anti-backlash gear in your radio, the double gear in question. When reinstalled in the radio gear train, you compress the springs one tooth, so that the teeth on both halves of this gear line up together. You maintain that compression when you bring this double gear in mesh with the other "plain" gear in the radio. Then when you release it, the springs force the two halves of your special gear outwards to fill up all of the "slop" space in the mesh between this double gear and the plain gear. The lost motion that would be caused by looseness of mesh between two plain gears is gone.

In addition, the split gear compensates for metal wearing away from the gear teeth. As metal wears away over time, the springs keep pressing the teeth outward so that perfect mesh is maintained.

Very well put!

I have had more than one case where the two gears are "stuck" together and will not rotate against each other, thus defeating the anti-backlash function. This is likely due to the oil or grease becoming gummed up and changing to concrete. I usually soak the gear set in lacquer thinner for awhile until one will move. Once free, apply good quality oil to the crack between the gears (I use turbine oil).

Ok, I got the tuner disassembled and I put it in a denatured alcohol bath in my ultrasonic cleaner.

It looks really terrific now. I went for alcohol rather than something like acetone or mineral spirits, thinking it would be easier on any resin parts. It looks jim dandy so far so I'm hoping I guessed correctly.

I had a tough time working with the teensy ball bearings. They are WAY too small to pick up with my fingers, and the space they have to go into in the race is too small for them too. I ended up resorting to some light grease on the end of a fine-tipped screwdriver... and was able to scrape them off on the lip of the race. By golly that worked as expected. It looks like I didn't lose any either!

I used a light machine oil for the ball bearings. It's a product called Slip 2000 EWL which is an all-synthetic gun oil. It's very thin but very slippery.

For the large axial ball bearing, I used some of the light grease. Actually, I'm not sure you'd call it a grease so much as a gel. It stays in place better than oil and held the bearing in the cup while I re-assembled the end caps. This stuff is super slick and has an inclination to stay where it's put.

It took a good bit of adjusting to get a fit that was *just* between flopping around under it's own weight and just a light, velvety resistance that moved with little effort. But I believe that's what I have achieved. The end purpose of the whole fussy business!

I should probably go ahead and replace the resistor on the tuner. It's been through the ultrasonic alcohol bath, and it'll never be easier to get to than it is right now.

And then I get to put the string-wheels back on it. And try to figure out the correct orientation. Should have taken a pic before disassembly. Oops. That'll learn me.

Oh crikey!

I just got what you guys were trying to tell me.

Here I had been thinking this big brass gear was all one piece. It is NOT. [/banghead]

It's actually TWO gears that ride atop one another. Now I understand about the backlash thing.

I'm pretty sure I can cut down the spring from a ball point pen and make it work there. NOW I *get* how it is supposed to work!

Thanks everyone.