I picked up a client's Twister and while cleaning it up made a surprising discovery - unfortunately only after I completed the top-side teardown . I knew the disc was noisy and slow (magnet worked tho!) and I figured the motor just needed a good cleaning like the rest of the game... but it turned out that directly beneath the spindle for the spinning magna-disc, was a blob of grease (?!)... and once I wiped that away I found this:

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It's bulged into a prone "bubble" about 1mm deep, which non-coincidentally is how low the disc sits below the surrounding playfield. It might yet be possible to raise the disc level, but my concern is the cracking bubble may finally give way at some point. I'm sure the magnet pulling the disc (and spindle) downward with the weight of 3-5 balls attached had something to do with this, and perhaps it was inevitable.

The spindle gear is of course now misaligned but still engaged with the motor pinion, if perhaps not fully properly. So it works, but again - noisy, slow, and for how long? That spindle boring into the bubble, being pulled down by a magnet, WILL cause this to yield and break away "someday".

Now I'm sure new motors are either NLA or stupid expensive... so is it possible to fix this? I'm thinking to drill out the rivets to open the case, and then perhaps line the inside of the "bubble" with JB weld. Or is there a bushing that will readily seal this crack? Any other ideas? Is this a typical problem on Twister?
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Good to know, that's what I was thinking as well. I mean it SEEMS like that should work! But I'm always leery of "well crap, not so easy as it seems" landmines because once I open that motor, there's no going back (especially with my luck, that'll be the thing that finally makes the bubble burst).

But I agree that JB Weld to seal the crack, fill the bubble, and bond a 1mm washer/bushing for proper height should work very well/enough in theory.

Duh, I just noticed the threaded bosses flanking each side of the spindle bearing: might be possible to screw in a reinforcing keeper-strap across the bubble too!

Good ol' Multiproducts! It is one of their units. Haven't tracked them into this yet, wanted to better understand what's going on. So I cracked it open and here we are:

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Zoom in and you can see the hairline cracks, which is how the lubricant weeped out even though light can't pass through yet. But oddly enough, I'm wondering if the "bubble" was not a failure, but an original casting profile to match the spindle:

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Either way, a repair is needed. The sleeve bushing in the original bore looks fine, and there were no shavings to indicate that a thrust plate was ground down. So I'm now unsure how to line the bubble crack with an internal patch, while retaining the conical profile ("bowl") matching the spindle point.

A trick I learned for worn spindles in jukebox repair, is you can put a single ball bearing in the "point" of a spindle bowl to reduce friction and act as a shim to improve motor performance. But in this application, that would focus more force directly on the crack and thereby increase the chance of failure. Bad idea.

So I'm leaning toward using some JB Weld as a laminate on the outside, further held in place by a retainer-plate I'll have to make and screw into those coincidentally convenient bosses.

OH and for those keeping score: remember my hesitance above ("I'm always leery of "well crap, not so easy as it seems" landmines...")? Yeah. My hesitance is well founded: for some dumb reason this was the single most stupidly uncooperative motor I've ever tried to drill open. Those sleeve rivets just WOULD NOT COME OUT. I can't explain it! At some point while drilling to increase the bore within the rivet (the heads were long gone) the sleeves would catch the drill bit and spin inside the frame. Which should have meant they were actually loose enough to extract but NOPE. And of course at that point, their spinning meant they couldn't be drilled anymore (and extracting the stuck drill bit was a PAIN. And yet the bit came out, but not the sleeve?!?! What the hell?!). Eventually though much drama and redneck hackery I got 3 of them out but the 4th steadfastly refused; I had to use a Dremel cut-off to break it at the joint. Even now, you can look in that bore and see it's as if the rivet and frame fused into a single, thicker unit. Anyway, it's always "something" with projects like this. What looked like it should have taken 10 mins tops with a drill, took almost 90 with vise-grips, pliers, a press, and other tools and desperate risky tomfoolery. Bleah!

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Finally posting the followup here in case it helps someone else in the future: I did repair the motor and it is working well so far!

I decided to pursue the concept of a reinforcing plate beneath the spindle bearing, using the pre-tapped holes flanking the bearing spindle as convenient anchor points. I planned to fill and laminate the spindle bearing cracks with JB Weld and attach the plate over that, sandwiching the epoxy for additional durability.

For the plate, I of course first looked to see if I had any handy stock with holes in the right place and it turns out that pipe strap indeed has them just about right! So I cut and flattened a section; the hole spacing was maybe about .25mm narrow: just enough to force an 8-32 screw into the housing bores, which would further keep the strap straight and flat under tension. The solid section between the strap holes is centered directly under the spindle point which is again, reinforced with a layer of JB Weld applied right before attaching the plate. Excess JB Weld seeped through the holes; if I'd mixed a bit more / enough I could have better filled and overlayed the holes for a cleaner appearance. By the time I realized that, the setting time of what I'd already applied was working against me, so I left well enough alone.

It's worth noting the balls' dropping directly onto the mag core at the center of the disc, literally pounds the spindle point downward into the bearing! So the original damage is inevitable, AND an even better plate solution would use a piece of angled steel, like an L or U channel, which would be far more rigid and resisitive to deflection under such impacts. However, you'd likely have to drill your own holes in such a piece. This household-hardware part was quick enough to try and should be at least as durable as what was there, which did last a long time. Hopefully it will last the game's future service life with its worst days behind it.

The only thing I should probably do is dress (file) the ends of the strap to remove the sharp edges.

Anyway, I hope this is helpful!

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