Replacement screws for 200A harp & improved sustain / note decay!

[JamieOxford]

Does anyone know what size/thread these screws are on my Wurli 200A? (The middle/coarse harp screws)
They're killing the sustain of a few notes when tightened and are too short/worn to be shimmed with card as the service manual suggests.
Thanks !

[velo-hobo]

Those are sheet metal screws, not machine screws, so the threads are not exactly standardized nor would I imagine the manufacturing tolerances are very tight.

They also thread into clip nuts. If the clip nuts are damaged or worn, then you may need to replace those bits if repairing is not possible (for example if the metal where the screw threads in is deformed and can be re-formed to a more functional condition)

I would suggest just taking one of those screws to a hardware store and trying to find one or more good matches, then doing a test with one only to see how it threads in, before committing to doing the rest like that.

These harp screws need to be somewhat fine-adjustable and they need to hold position, since any of them being too-loose or too-tight can affect the sound significantly. I"ve never needed to shim a harp mount, but I suppose it is possible, for example if the wooden case warps and changes the relative positions of the harp mounts.

[JamieOxford]

Thanks velo-hobo! I've since disassembled further and ordered a few bits to replace the original screws (new M5 self tapping screws and "spire clips" in the post).

The service manual suggests paper keybed shims for the harp to fix dull/quickly decaying notes, and while this works a bit, I've found 1mm rubber washers are a lot better! I've also added these between the harp and pickup shield to remove some acoustic rattles I had. Hopefully the harp will only be ~0.5mm higher after reattaching everything so I won't have to adjust the letoff much.

It's amazing how much the resonance of particular notes are affected by the harp screws though! 1/4 turn makes a huge amount of difference.

[velo-hobo]

Good on ya, yes the harp assembly can sometimes seem black magic between taming resonance, rattles, and dead notes

Whatever makes it work and will hold adjustment

[JamieOxford]

So it turns out M5 self tapping screws fit the original U clips perfectly. I used these 35mm ones cut down a bit with a hacksaw: Phillips Hex Washer Self Tapping Screws, M5 x 35mm

I also used rubber washers in place of the plastic washers below the harp which has improved sustain immensely and reduced most of the weird overtones. I put 3 at the front and 4 at the back in the bass section, and replaced the metal washers on top with rubber ones. I also used some below the pickup covers to tame other resonances.

Just waiting on some more washers to arrive to finish the treble section, but it's already singing way more than it ever has done!