Refitting Piston Valves

I started plating and refitting valves in about 1981 (actually a few unsuccessful attempts in 1978), without the advantage of a honing machine. It is possible to do an excellent refit this way, but fraught with challenges and excessive time. It involves building up only enough plating that the pistons can be lapped into the casings (about .001” to .002”) and typically required three to six rounds of buildup of copper or silver and lapping before achieving a good fitting surface.

If too much plating is applied, The pistons won’t insert into the casing for lapping. I was taught to use a “lapping block” for this purpose (first photo). Lapping blocks are made of hardwood which has enough give that it removes more metal around the ports, where it takes less pressure to abrade, but where it is most important to have a tight fit. I decided that this was not ideal and stopped using them. The external hone, using the same mechanical conception, removes metal precisely and evenly when used correctly.

Then the final layer of nickel is applied and lapped in. If the nickel is not thick enough, it is likely to lap through at the top or bottom of the piston and needs another layer. If it is hard nickel, it must be stripped and attempted again. The plating shop that I used at the time used grey nickel that could be built up over a previous layer. Of course, too much nickel would necessitate some method of removing some without ruining the perfect cylinder that was needed. For a few years, I had pistons honed by a local shop that specialized in lapping and honing, but still missed the mark about 10% of the time.

When I learned that I could get valves plated and refit by Dave Seacrest (now retired) at Anderson Silver Plating at a cost that I could never match, I used this service for over ten years. During this time, I wasn’t fitting many pistons myself, mostly oversize pistons that are available for Bach trumpets.

When Joe Marcinkiewicz was moving his workshop into his first commercial location (about 1986) he was getting rid of his old Sunnen honing machine. He had gotten this vintage machine from Benge and it had been used in the Los Angeles Olds factory before Benge. You can see that I still have that machine in the second photo. Once I got the necessary tooling: mandrels for honing the casings and external hone body for the pistons, along with the correctly sized stones, shoes etc, I was finally able to accurately size these parts for the final lapping.

Starting with the basics: The first job is to hone the casings until they are true and free from deep pits or other damage so that a piston can be fitted tightly. If the pistons are damaged, they will need to be repaired, straightened, ports patched and in extreme cases, dents filled with solder. Another option when the tolerance is extreme is to sleeve the pistons, as I describe in another page.

Then, with careful measurements, I have to decide how much plating will need to be built up. The most accurate method that I have found for measuring the inside diameter of the casings is with a plug gauge set as in the third photo. These are normally in increments of .001” and based on how tightly they fit, I know which is closest to the exact diameter.

Traditionally, the pistons are built up with copper plating, honed to about .002” undersize, then built up with nickel plating, honed and then lapped. I learned that it was most efficient, since I don’t have my own plating facility, to have the correct amount of plating built up with nickel in one trip to the plating shop, so that when I hone them to size, they are ready for the final lapping. I have to be very sure of the amount of build up; if it is too little, they will need to be stripped to the base metal again and built up with nickel to the right dimension. In the easier cases, when the pistons have never been damaged and are still close to being perfect cylinders, I will ask for only .001” more than the desired final diameter. If the pistons are less perfect, it takes a bit more judgement and I might try to measure any low spots to estimate the amount of build up needed. It makes more sense to hone the piston to a perfect cylinder first to determine the build up needed. This dilemma can also be eliminated by building up the pistons with copper first, hone to at least .001” undersize and then decide if they need more build up with copper or are ready for the nickel.

The plating builds up inside the ports at a slower rate than on the outside surfaces of the pistons, but still, it will reduce the bore size inside the ports. If I need more than several thousandths of an inch (diameter) built up or just to make the job the best possible, I prefer to mask the ports before sending them off for plating. I brush on masking lacquer with several coats and carefully clean any of it off the piston surface. The second photo shows pistons after returning from Anderson Silver Plating with the necessary build up of hard nickel plating and the (green) masking still in all but one.

I had masked the ports in some of the valve refits that I did in the 1980s, but never had complete success, especially in the number of hours spent. With the help of crack brass repairman, Mark Metzler of Elkhart, Indiana, in more recent years, I was finally able to make this process efficient enough to be profitable.

After removing the masking lacquer, I grind off the ridge of nickel from the inside edge of each port with a diamond burr as shown below.

Because the bright nickel plating builds up faster at the top and bottom of the pistons, I prefer to remove some of this with a diamond sharpening stone. This can be done on the machine with the external hone, but seems crude work for a fine device and necessitates truing the stones at least once for each piston.

While honing the pistons (second photo) I constantly check the diameter with a micrometer. When removing a lot of material, I use fairly stiff pressure with the external hone body, but as it gets close, I back off and take my time. This eliminates the removal of more material around/between ports, which would make a lesser fit. When I get within .001” in diameter, I start checking by inserting in the casing. Once it just goes in, it is ready to lap. I’ve made lapping handles with threads to fit whatever pistons I’m fitting.

The final lapping is done with 1200 grit garnet compound. Once the valves feel like they are fit (little resistance even after applying fresh compound) I lap for several more minutes. This almost completely eliminates the need for more lapping when assembling the instrument later but still achieves a very tight fit.

The eighth photo shows a finished set of pistons that had been masked and the last, a set without masking.