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Should the harp bolts be tight? I've got a little buzz on my piano and was poking around at this and that. I found that 4 of the harp bolts are loose enough to wiggle the washer under the bolt. Is this normal for those bolts to be a little loose or should they be snug?

I'll call in a tech to do the snugging if this is not normal. It just seemed to me that the washers could be vibrating and causing the buzz.

The plate bolts around the perimeter should be snug.

Greetings,
Platebolts need to be snug, certainly tight enough to keep washers from rattling. Their purpose is to keep the plate held as flat as possible against the string tension, as well as some acoustic coupling. There are some caveats, both generic and specific to Knabe.

The bolts will be tighter in the summer than the winter, and if you tighten them in the dryness, the return of humidity will crush wood fiber against the steel threads, and the next winter they will be loose, again. If continually tightened in the dry season, the bolt will eventually make a complete revolution and strip the threads in the case. For this reason, I only snug bolts in the summer. I learned that at the school, as I keep records of my maintenance, and those records showed that I was tightening the same pianos every winter.

To the Knabe specifically; unlike most brands, Knabes often have a plate bolt that is free-floating, i.e., there is nothing under the plate for the bolt to tighten down on. This is most common on the first bolt of the treble. If one begins tightening that upper bolt until it locks down, the plate will probably crack. Knabe also used acorn nuts on plate bolts on many of their models. These will not loosen when the weather dries out, since the nut tightens the plate against a steel shoulder on the bolt. However, it pays to check that the acorn nuts actually reach the plate, since there have been instances where there was a millimeter or so more threads on the bolt than there were in the acorn nut, and the nut would tighten on the bolt and begin turning it in the wood. This flexes the plate down, and will also break a plate, (DAMHIK!!)

All in all, I think some professional experience might be a good investment for this .
regards,

Thank you for the information. Technician is coming by next week. He also owns and plays a Knabe in his own home, so I'm thinking I'll be in good hands.

I'd really like this little buzz to go away, as it is driving me a bit crazy. There's a faint buzz on D2 - B2, but E2 is like a spike driving into my eardrum, the rest of the notes sound pretty sweet.

If the issue is not the bolts is it possible that one of the string windings is loose? The piano was restrung a year ago. It sounds like something metallic vibrating against something else metallic. I don't see any obvious cracks in the soundboard or gaps in the bridges.

Loose plate washers certainly can buzz. Ed Foote has a good point but some parts of the country can be more humid in winter than in summer, so I'd revise his suggestion to say "avoid the dry time of year, and snugg bolts when it's humid". Rubber cement can be used to stop a loose washer from buzzing if tightening the screw is deemed unwise. I never use excessive pressure, unless I've removed the plate and know what's supporting it.

In Florida, those homes that turn off the A/C during the winter will be more humid in winter and drier in summer. Some folks get that August A/C bill, and turn off the A/C in September, and their homes are 70% RH or higher. Those pianos climb sharp in winter, opposite to what happens in most other parts of the USA.

Use some masking tape to restrain the washer from movement until your tech can adjust things.

Ed, thank you. I put some paper shims under the washers tonight (didn't have any tape) to isolate them from the plate a bit. Already the difference is enormous. I'm hoping after the tech adjusts things it's going to be pretty sweet.

..... But remember that the longer that masking tape is left stuck to a surface, the more difficult it becomes to remove it cleanly.

You will do no harm turning the bolts down only just enough to stop the rattle and no more. Have your tuner check them on the next visit before tuning. (snugging them can affect tuning.