Fixing a leak

[Nathan]

My concertina is leaking a bit between the action box and the bellows frame, and I'm wondering if there's anything I can do myself to fix it.

 

If I push the ends together without any keys down, I can feel where the air is coming out. I tried putting some painter's tape over that spot and it works reasonably well -- while it still leaks some, the instrument feels much better to play. But I'd like to have a more permanent (and nicer looking) fix if possible.

[Marien]

It appears that the air finds a way to get out of the bellows somewhere where it should not. 

If it is an lachenal or another brand of old english concertina's there may be lots of causes, such as

- blocks to hold up the reed plate have loosened.    

- a reed or action plate may be warped, 

- a crack in the action plate

- shrinkage of the reed plate, letting the air go around it

 

there may be more, and I suspect that answers may already be available somewhere in this forum...

 

Edited November 30, 2022 by Marien

[d.elliott]

I suspect that Marien has misunderstood your question. You have identified a leak site between the bellows frame and the underside of the pad board. There are two initial actions to take: firstly, rough up the nap of the chamois leather gasket and secondly, check the underside of the padboard for damage, shrinkage away from the surrounding action box frame or general unevenness. If there is damage, shrinkage etc you need to do whatever is appropriate to block any air paths. I is usually glue failure around the pad board, if it is not the condition of the bellows frame gasket. 

[Nathan]

Thanks. The padboard has pulled away from the action box frame a tiny bit in a couple places. The picture below is the worst spot, which lines up with the location of the leak. Should I just fill this with a little bit of PVA glue and then sand it down?

 

The padboard doesn't have any obvious unevenness, but if I lay a metal ruler across the sides I can see a little bit of daylight in places. The leaky spot doesn't look any worse than the other sides.

 

The gasket also looks pretty worn, and is particularly bad near the leak (see other picture).

[alex_holden]

Another thing to check is that the threaded section of the end bolt is long enough. I have seen some instruments where the bolt runs out of thread and stops turning before it has compressed the action box against the bellows frame.

[Theo]

Your pad board looks fine. That tiny gap under the veneer is to close to the outside to be the source of the air leak.

 

4 hours ago, alex_holden said:

Another thing to check is that the threaded section of the end bolt is long enough. I have seen some instruments where the bolt runs out of thread and stops turning before it has compressed the action box against the bellows frame.

 

This is much more likely, especially as sometimes happens the end bolts have been overtightened in the past and the bolt heads have worn their way down into the wood.

[SteveS]

1 hour ago, Theo said:

 

This is much more likely, especially as sometimes happens the end bolts have been overtightened in the past and the bolt heads have worn their way down into the wood.

I've seen this many times - and it's not an easy thing to repair.

Bolts are overtightened in the mistaken belief that doing so will fix leaks - the leaks are often caused by the chamois being over compressed - I've seen chamois so compressed that it looks like wood and missing entirely.  The remedial action should have been in this case to replace the chamois.

[d.elliott]

Your 1st picture shows the casing veneer a bit lifted, not likely to be any issue in this problem. The second picture shows a compress edge gasket which could benefit from fluffing up a bit. Taking the point of screws digging into the action box casing, you can test this by making some little card washers and see if the increased 'nip' helps. If it does, then get some appropriate brass washers of the internet. Probably 10BA small.

[Nathan]

Thanks everyone for the advice.

 

I don't think the screws are running out of thread. I'm able to tighten them down to the point where they feel snug -- and I assume I don't want to crank really hard on them. The outer cover of the action box is metal so there's no risk of the bolt heads digging in.

 

So the gasket seems to be the most likely culprit. Is there any particular technique to fluffing it up?

[Wally Carroll]

The easiest way to fluff it up is to use your thumbnail. 

[d.elliott]

as per Wally, thumb nail or the tip of a screwdriver (but not too hard)