Why this article?
As a conscientious maker of horns I´m very interested, that the buyer for a very long period will enjoy his investment. The life span of an Engelbert Schmid Horn can be almost unlimited, but also any other make can last very long at the right maintenance. Generally it’s a fact, that horns, and brass instruments at all, are rarely dying by being played, but are destroyed by repairmen who don´t know the correct craft. So many of them are no repairmen, but “destroymen”. Why exactly by these “experts”? Because they never have produced a machine, never have had to fight for every singe hundreds of a millimeter.
The principle of a valve:
In wet condition of the inside tightening areas the valve has to be airtight also at the air pressure in Fortissimo. For this the tolerance in diameter between the rotor and the casing has to be within 5 to 8 hundreds of a mm. We aim to constantly achieving the 5/100 mm which are the minimum for well running valves. New valves of good makers normally are so tight, that the instruments from the beginning provide a good ff. In the first 6 months the valves get even tighter because of the oxidation and lime deposit. This is one of the reasons why horns get even better after a certain blowing in time. The valve bearings need to have even less tolerance, the less the better. In diameter within 2/100 mm is ideal and possible. By this the valve is running only on the bearings, which always should have oil. If there is no oil in the bearings, condensation water and with it lime deposit may grow into the bearings. The valve inside is swimming in the condensation water respectively in thin valve oil. The bearings need medium thin oil, which does not evaporate too quickly. Most of the problems with sticking valves come from no oil being in the bearings, so allowing the access of lime deposit (the calcium in the lime deposit is a very bad lubricant), or from bearings with too much tolerance, that the normally calcium covered rotor inside can touch the also lime deposit covered casing.
How should you treat the valves, that they are running reliably and not get old?
See the following good advices:
The most important repair at every overhaul is reseating the bearings, in order to have no side play at all any more, and reseating the upper bearing plate, for eliminating eventual up and down play. For this you do need a reseating tool (like f. i. from Böhm in Neustadt, www.boehmtools.de) with the according clamps. A clamp produces a triangle. You have to turn the bearing shrinking tool by 60° in order to achieve a hexagon and in the practical reality a circular shrinking. Then go up half the bearing and repeat the procedure. This means 4 short steps per bearing! Only then you have reseated well at the whole length! Develop a sense for the right dosage! If you once have reseated too much, you have to lap the axis in the bearing carefully with a grinding powder of size 1200 (which means that 1200 grains fit on 1 square mm!). After that you have to remove the grinding powder absolutely. Never you should lap the inside of the valve, and also never (one million times never) put the rotor into any bath for removing the lime deposit, or even worse polish the rotor! There is no bath on the world which takes away the lime deposit and does not remove metal! Even if you only take away the oxidation it’s a loss of metal! Very quickly you reach the barely acceptable 8/100 tolerance, and next time already the not any more acceptable 10/100 mm! Be aware: If you only take away 1/100 of the material, this amounts on 4/100 tolerance in diameter already (1/100 on each side of the rotor and 1/100 on each side of the casing)! You have reached the 10/100 mm tolerance and have destroyed the instrument!
And this as a “specialist”! You should be made responsible for an replacement instrument and you should be banned from your profession! Please don´t be shocked, but think about it! At the end you will be grateful to me for this brusque hint!
Turn the calcium covered rotor in its own soup with a crank lever at the upper bearing plate taken away. This way you chafe the excessive lime deposit and wipe it away with a cloth! The remaining lime deposite is positive! It makes the rotor rounder (no turned part on the world is absolutely perfect!), the film of liquid in which the rotor is swimming is more even and the valve is running better! Excessive lime deposit you remove with a scraper tool.
At very strong lime deposit by the musician one day you have to decalcify the instrument without the rotors and the bearing plates. Do this as rarely as possible! Eventually only every 5 years, and then only for a minimum of time. We in our workshop watch exactly, when the calcium is away and neutralize the instrument then immediately. About 1 minute in a 15% sulfuric acid bath is enough. Many repairmen, without thinking (“much helps much”) put the instrument in such a bath for 1 hour and so have 60 times the abrasion of metal at the casings! At responsible use of decalcification and the correct treatment of the rotors a machine can stay functional for 100 years indeed, also at professional use of the instrument. The staggering praxis of the repairmen is a life time of 5 to 10 years.
For reseating the upper bearing plate it makes sense to get a bench motor with the corresponding clamps. With this you are quicker than on the drilling lathe. The sensitive fixing of the bearing plate into the clamp, centering the level and taking away the few 100th of mm by hand provides better results than on the drilling lathe. Her you can see both sides of Engelbert Schmid valves from outside:
At Engelbert Schmid Horns there is enough distance at the stopper side between the stopper and the bearing, so you can reach the correct corner for oiling easily without oiling the silicones. At the screw cup side the correct spot for oiling is at the air marks. At Engelbert Schmid Horns due to the geometric construction of the air marks the oil is growing very well into the whole inner bearing area. Eventual oiling inside with thin valve oil is done through the side hole without the danger to wash slide grease from the slides into the valve.
At mistreated und so untight valves of the traditional brands there is no entirely satisfying repair. Enlarging the rotors by galvanization (rebuilding the valves) can provide an improvement for some time, but often does not provide the necessary tightness to the valve absolutely never gives back the original running abilities. To exchange the whole machine by a new one is expensive and often changes the instrument. At Engelbert Schmid Horns mistreated valves always are completely repairable, - for a reasonable price! At this machine system its possible without problem to exchange the rotors and the valve is rest into the new condition. In the rare case of too much loss of metal in the casings these are calibrated to 1/10th bigger and corresponding bigger rotors and bearing plates are inserted.
So, I should let the things slide with the repair methods? :-) No, - again and again it’s a pain for my soul to see, how long hornplayers labour away with inefficient, untight horns, and that they normally have to pay themselves for the not so inexpensive repair, because they cannot make anybody responsible for that.