lapping a valve

[sirjohna]

I just bought new jinbao euphonium. Out of the case the valves were working normal but when I tried to remove the second valve it was near impossible to remove. I'm suspecting that the tight point is at very top of the valve caseing. It''s a little important that i fix this myself. Any hints ? . If it was just a burr at the top of the piston threads would you dare use the finest emery paper. Should I bite the bullet and make the long trek to a technician. The valve is out now

[magolmaethor]

Unless you have experience in repair, I would not suggest attempting to lap the valve yourself. Bringing the horn to an experienced, reputable brass technician can save you hundreds of dollars in the long run in parts, labor, etc. I understand that good repairmen can be hard to locate (distance and expenses permitted), but you will not regret it. If you provide a location, I'm sure some of the more seasoned posters here can suggest a tech in your area.

[sirjohna]

I bought it directly from Jinbao, so shipping back might be a problem. Despite asking for advice here, I jumped the gun and took the emery paper to it. I guess for FYI if (anyone else dares), I started with 2000 fine emery and got nowhere so I went to 600 grit. I concentrated on the very top lip of the caseing and started to concentrate on a place where I could see a small mark on the top of the caseing. I think I did very little "sanding" below 1 cm into the top. It seems to have worked after about a half hour of rubbing. All 3 valves are working equally. I did quite a bit of rinsing and plan to do some more before I play it too much.

[Dan Schultz]

Tubas that are built with any thought at all usually have a relief at the top of the casing. Shame on Jinbao!

There is nothing happening in the first 3/8" or so of the casing so it's safe to use a machinists scraper at the top of the casing. Also take a look inside the top caps. There should be a relief where the threads meet the inside of the top. If not... this condition could cause distortion of the tops of the casings if tightened too tightly.

ANY of these horns need to be thoroughly cleaned and deburred before being put into service.

[euphoni]

If you can't afford to send your horn back to the retailer, bring it to a local repair man, or send it to someone like Matt Walters from Dillon Music, you can use the method listed below to lap your valves. This method uses the pumice in Lava soap to strip down accumulations of rust, mold, gunk and metal on the valves so they fit better in the valve casings. Also, I've never tried this method on your brand of horn and results may vary from horn to horn, so proceed at your own risk.


1. Buy a bar of Lava soap.

2. Soak the Lava bar in a bowl of water for a couple days, or until bar is soft.

3. Dump water and you will be left with a soft bar of pumice(y) soap.

4a. Take a damp washcloth with a good bit of Lava on it, wrap around the valve and work it back and forth, up and down for a while.

4b. For older horns with lots of gunk build-up which may be accumulated inside the valve casing, you can even work a small bit of Lava between the valve and its casing; but a full dip/cleaning will be required afterwards to get all the pumice out of your horn.

5. After working it for a bit, you need to see how it fits in the casing. Trial and error; It'd be much better to do a little then try it out rather than going too far. You have to strike a balance where you want the valve to fit easily and easily go up and down, but with no 'play' or wiggle when the valve is inside the casing. Also, know that all valves are different and some are and have to be tighter inside the casing for it to work properly with the build of the horn. So, again, not too much.

6. Wash valves completely and oil before placing inside casing.

7. Rinse and repeat as needed.


Good luck!

[Dan Schultz]

.... 1. Buy a bar of Lava soap.....

I'm glad you mentioned that Lava Soap contains pumice. This stuff is not exactly the best material for lapping brass because it can (will) imbed in brass where it can/will continue to cause problems.

The lapping material of choice these days is garnet powder.... available in several grits at a reasonable cost.

[Art Hovey]

A dremel tool works well for removing metal or crud from the cylinder above the normal position of the piston top.