The solution to the problem is not as easy as it might seem. This problem could be caused by a "out of round valve", in which case, you would have to find a flat surface which you could roll the valve over to determine if it is straight. If it is not, place the valve upside down in the bottom of the valve casing. Rotate the valve until it is apparent where the valve is bent. Tap it softly with a rawhide or plastic hammer on the "high" spot. Work the valve into the casing slowly, do not force the valve into the casing. I like to let the valve fall into the casing, this way I know that it will work well when placed in the top of the valve casing.
If the valve is not "out of round", see if there are any dents present in the outer valve casing. To remove dents, place one of your mandrels in the casing and balance the weight of the horn on the apex of the dent (highspot!). Once you get the feel for holding the horn in this position, gently tap the outer most parts of the dent with a dent hammer. Continually check to see if the valve will go in the casing. Sometimes a dent can still be present on the outside but gone on the inside. Another technique I use forremoval of casing dents is to place the largest mandrel I have, that will fit into the casing, and hammer the mandrel itself. This requires two people-
1) Put the mandrel in the casing
2) Find the dent and balance weight of horn on the "high spot"
3) Apply pressure
4) Have helper hit the mandrel half way between the horn and the vise with a heavy object(sometimes a hammer is not enough/ a large piece of steel or fence post works very well)
5) Keep doing this until the valve slides in freely
NOTE: you have to be careful that you don't go too far and put the casing "out of round". Remember to check the valve fit often. It doesn't seem like this form of vibration would work but it actually works very well with the least amount of damage to the horn(ie. hammer divets, scratches, lost finish)
Lastly, pumice can be used to remove imperfections in a valve casing but generally should not be used to remove high spots and dents. Most of the time you end up removing too much material and cause the valve to rideunevenly in the casing. If you use too much "Lapping" you can cause far worseproblems than what you were trying to fix. A company called American GrindingProducts, aka USP, has many different grades of lapping compounds which areuseful for fitting valves and slides. I use some of their products and find them to be be of very high quality. It is important not to use too abrasive of a compound since you want to maintain tight control on the amount of materialyou are removing. You can use household pumice if you want but be careful to notice what affect it is having on the valve casing. Pumice has a tendency to break down during use becoming finer as it is used. It is also hard to clean away from the horn. After all lapping, make sure that all the lappingcompound is removed before reassembly. One more thing- use oil with the lappingcompounds ( I use SAE30 weight motor oil/non-detergent). The oil will make it alot easier to move the parts when lapping. It also tends to keep the lapping compound in one place unlike water which allows the compound to spreadall over the horn.
Mailus any questions you may have concerning this topic.
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