Lapping valves?

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12 okt 2008 18:41 #184 by Edward House
Lapping valves? was created by Edward House
A few months ago I purchased a used horn. The manufacturer tells me it was made in early 1990. Whoever had it last did not take good care of it. Lately I have been having problems with the valves:( . He cleaned them out and gave me this report.

"Unusual “silver colored particles” were imbedded in the no. 3 rotor. My first impression was that this was solder from the factory as there is no obvious indication of post factory assembly repair work. The no. 3 valve refuses to turn freely past approx. 10 degrees of rotation past the normal 90 degree angle.
The no. 1 valve lower bearing / bushing is in serious need of re-colleting to include the upper bearing as visual movement is noted.
Oxidation build up on the rotor casings is nominal with typical “light” adhesion of the “green slime” that is typical on rotor ports. I recommend use of garnet lapping compound on all rotors and bearing sleeves after colleting all bearings, with particular concern to no. 1 & 4 rotors. Play on no. 3 valve is showing some play as well, but not to the extent of no. 1 valve.
Opening upper inner cap clearance +/- 002” did not seem to benefit valve action on no. 3 valve."

I have heard that valves should only be lapped on a new horn and after a valve rebuild due to the fact it can cause compression loss. This repairman assures me that it will not harm the valves because the compound will not widen the clearance between valve and casing beyond the factory tolerance. He assures me that they will be just fine. I don't question his skill to complete the lapping, I am just hesitant of the process in general. Has anyone had their valves lapped and did it hurt the compression?
Thank you for your input!

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13 okt 2008 09:30 #185 by Molly White
Replied by Molly White on topic Lapping valves?
I paid considerable money on valve work about 2 years ago, and I feel it was a good thing to do. In my case, I had the valves completely re-built. Compression improved considerably, although I feel it's not as good as when the horn was new. I have a very high quality instrument, but it was 20+ years old and harder to play than it needed to be. One person warned me against the valve work - said I would hate the horn. But I was at the point I disliked the horn anyway, so I figured what did I have to lose? In my case, I'm very happy with how things worked out and feel I have a really top quality horn again, for far less than it would have cost me to buy another instrument of comparable quality. I hope this helps you put your own situation in perspective - ie, what's the horn's over all quality? What would a new horn cost you compared to the valve work? Is your compression all that great now? Does the horn play as well as you'd like or could it be better? What else would you spend the money on? Hope this helps.

Molly

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30 okt 2008 15:14 #190 by Martin Künkler
Replied by Martin Künkler on topic Lapping valves?
Hello Edward.

I think, the former owner of Your horn was a person who didnt like his/her instrument. He/she never watched to it and I am asure, it never was cleaned up inside.
Valve repair is a difficult thing. If the brown/green coating (patina) will be smooth or polished off form the contact surface, the valves loose thightness.
Inside the valveopenings (aircanals) You can polish it.
If the upper bearings (at the valvehead) are wear off, its possible, to repair it. The upper bearings will be jolt and with polishpaste You smooth it until it will fit (will need some hours!) Smooth it by HAND! NEVER use a drillmachine! It wobbles! And so the bearing is not 100% straight. For this work, You can buy a special handcrank (e.g. at "Ferro tools").
If You can move the valve up and down in its casing, You have to put the lower bearingplate on the lathe and turn the rabbet some /100 Millimeter deeper. If it has no rabbet, reduce its diameter step by step. So it goes deeper into the caseing and the differnce is off.
If the lower bearing is wear off, turn a new bearingplate (bearingcap) on the lathe.
You wrote, that one valve will not turn 90°. May be, the valve (the upper bearingpivot) is bent. It is possible, to hammer it straight. But thats not possible, if the valve is made from castbrass! It will break under the hammer! Or there is a little burr at the lower bearingplate or inside the case or at the valvebody.
Further You wrote, that green slime is at the valveports. If You will clean up Your horn inside all six month, You never will have mud inside. But for a complete cleaning, You have to remove the valves. Use a cleaning-set like "Reka". (If You can not buy it in America, please contact me.) Things like HW-Brass safer are not strong enough to remove old mud. If the mud is so strong, that You need a file, forget it! Take a fexible cleaner with a brassbrush into a drillmachine, put some dishes cleaning solvent on it and mill the mud out. Clean up the horn with a lot of water, because the rests of the solvent/mud will become lumpy.
And if You grease Your slides, never push the old grease into the valves. Its residue become lumpy and the valve will stock. (Use Hetman No 7.)
But I have a question: In America, string action is favored. How is it possible, that the valves are so bad after only 20 years of use? At the string action, the leverpower is very equal and its influence to the bearings is not as strong as at a connection by rods.
Are the valvecasings made from brass or from nickelsilver? What kind of horn is it (mark or model)?

I hope, You will understand, what I mean, because my english is very bad!

Regards, Martin

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