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For a few months I've had the use of a Miraphone 186 BBb. Returning it to its owner on Tuesday, and have been cleaning and lubricating it. So I went to oil the valves in the usual way: removed the bottom caps of the valves and put some oil on the end of the valve, screw the caps back on.

But the fourth valve was better before oiling it. When I put the cap back on, it jammed. I had not touched the center screw, but even so, I loosened it now, then finally took it out entirely. The valve jams hard when the cap is screwed on beyond a certain point where it is still loose.

Any ideas would be appreciated!

What did you oil it with?
I always put rotary oil on rotary valves through the slides.

I used Hetman Rotor Oil ("Lubricant 12"). I put some in through the slide also.

Hmmm.... perhaps the back bearing plate is not seated properly.

TubaTinker wrote:Hmmm.... perhaps the back bearing plate is not seated properly.

That's a good idea. I'll check. Thanks...

Apparently some crud came loose when I removed the cap. Muriatic acid bath, voila.

Good job! Glad it worked out.

In some cases like this the solution is much simpler: don’t tighten the bottom cap so hard that it affects the end bearing.

Klaus

Yes, Klaus, I do that on my 186 - just finger ever so slightly snug. But the OP didn't even get it back on all the way before it jammed, pointing to the actual problem.

Speaking of which, my 186 has the little setscrews in the bottom valve caps. Do they really work to keep the rotors aligned along the axis? I confess to never having tried to align them, but keep them loose like Klaus says to keep the spindles from binding.

I reread the OP and found I addressed the original problem even more exactly, than I thought at first, because my experience in that matter comes from a certain French horn belonging to a school where I taught.

Apparently the male threading sometimes is cut too far down the outside of the casing thereby allowing the cap touching the end spindle (goes whether the Miraphone screw is there or not, the horn was a Hoyer).

Threading allowing for too much tightening happens, also from wear. The pro reply is putting plumber’s silicone tape on the male thread. In a pinch a simple household accessory also works. I cut a snip of a plastic bag intended for storing/freezing food. As these come cheap, I always use a new bag.

Klaus

I reread the OP and found I addressed the original problem even more exactly, than I thought at first, because my experience in that matter comes from a certain French horn belonging to a school where I taught.

Apparently the male threading sometimes is cut too far down the outside of the casing thereby allowing the cap touching the end spindle (goes whether the Miraphone screw is there or not, the horn was a Hoyer).

Threading allowing for too much tightening happens, also from wear. The pro reply is putting plumber’s silicone tape on the male thread. In a pinch a simple household accessory also works. I cut a snip of a plastic bag intended for storing/freezing food. As these come cheap, I always use a new bag.

Klaus

imperialbari wrote:I reread the OP and found I addressed the original problem even more exactly, than I thought at first, because my experience in that matter comes from a certain French horn belonging to a school where I taught.

Apparently the male threading sometimes is cut too far down the outside of the casing thereby allowing the cap touching the end spindle (goes whether the Miraphone screw is there or not, the horn was a Hoyer).

Threading allowing for too much tightening happens, also from wear. The pro reply is putting plumber’s silicone tape on the male thread. In a pinch a simple household accessory also works. I cut a snip of a plastic bag intended for storing/freezing food. As these come cheap, I always use a new bag.

Klaus

Well, at any rate I had not overtightened the cap.

If I was doing that, presumably one or more of the other three valves would have had the same issue. None did. It was just junk in the valve. Thanks though.

imperialbari wrote:In some cases like this the solution is much simpler: don’t tighten the bottom cap so hard that it affects the end bearing.

Klaus

If the rotor is working properly and has the correct clearances... it's not possible to overtighten the bottom cap... unless, of course, those goofy 'adjusting' screws are in too far.

The rear bearing plate has to be firmly seated into the rotor housing and the cap actually bottoms out on the rotor housing... or on a lip on the bearing plate which bottoms out on the housing.