what is "lapping the valves"?

[Jeff Keller]

I took my PT-6 into the shop the other day to have the rotors serviced. When I asked for an estimate they couldn't give me one due to the fact that they may have to lapp the valves. What does lapp the valves mean?? I've heard it many times but never had they nerve to speak up and ask.

Jeff

[tubaman5150]

Lapping is where a repair person applies a liquid or paste lapping compound to the valves and then usually rotates them until they are properly fit. The lapping compound contains an fine abrasive grit to accomplish this.

[Tubaryan12]

Thanks for asking and answering that question...you wern't the only one that wanted to know

[cjk]

I can't see how your rotors would need to be lapped unless it's a new horn. EVEN THEN, I doubt they would NEED to be lapped even if they were new. (unless they are slightly damaged...)

I would get a second opinion.

What I would do if I were you is get (pay?) somebody to SHOW you how to "service" your rotors yourself.

If you have enough coordination to sharpen a pencil or change a flat tire (or play the tuba?), then you should be able to handle dismantling and cleaning your rotors yourself.

[Dan Schultz]

Ok. Then what is venting the valves? I am just as curious about this as I am about the lapping. RA

When rotary valves are vented, a small hole is drilled through the rotor housing so pressures are released to atmosphere when the slide for that valve is pulled.

Also... about your earlier question about lapping... This is done on piston valves to establish proper clearances between the piston and the casing. On rotary valves this is not necessary unless the valves have been damaged. The only places where rotors actually touch the housing is at the bearings at each end of the rotor.

[BVD Press]

If you want to buy enough vinegar soak the whole horn in vinegar for about 30 minutes, rinse it out well with water, brush out the leadpipe and all the slide tubes when you rinse with water.

What would you tell the grocery clerk?

[Ryan_Beucke]

Wow, I never thought of cleaning my horn with vinegar...does it actually clean better than just soaking the horn in soapy water?

[Chuck(G)]

Doing the whole horn with vinegar is probably overkill. Just pull your main tuning slide, and cork the valve side. Pour vinegar in through the leadpipe until the valves and slides are filled, then cork the leadpipe. Leave it that way for a couple of hours, then drain, brush and rinse. If iit needs it, fill the main tuning slide and soak separately. Takes much less than a gallon of vinegar.

I suspect that a "whole horn" cleaning probably wouldn't be needed more than every couple of years.

[JayW]

I have always used white vinegar with a little mild dish soap and find this to work great as a regular system for cleaning my horn (about once every two months). It really helps get rid of the yucky stuff that tends to build up in the valves and slides......and the vinegar also kills any odor causing bacteria...Gotta Love a CLEAN SMELLING HORN.

[Chuck(G)]

That honest-to-goodness cleaner that Allied Supply sells (in powder form) is really quite harmless..

On the other hand, "Bright Dip" will dissolve your fingernails...

[TubaTodd82]

Just a note: I would not suggest disassembling your rotory valves unless you are willing to pay for extensive repair work or you have been trained to do so. I have seen many instances in which somebody who considers themself knowledgable in instrument repair taking there horn apart, puting it back together and it never working the same again, if at all. Rotors especially are very delicate, and sensitive, the slightest imperfection will cause the rotor not to work properly. Basically, spend the $100 once a year and have the horn cleaned by a professional. I promise it will save you money in the long run, and they will do a much better job than most ordinary people. Not to mention you will be supporting a local business.

And another side note: Bloke, I would not suggest using slime away or any other chemical unless again you have been trained to do so, which you may have been, but most of the readers on this site have not. If used improperly it can do major damage to the insides of the horn. (not removing all of the chemicals) I have seen many horns crack and literally fall apart because they were not properly cleaned after using those chemicals you consider harmless.

[ThomasDodd]

That honest-to-goodness cleaner that Allied Supply sells (in powder form) ...
The stuff works tons better than vinegar

The average bloke cannot get that stuff though, but vinigar is readilly found. It might take lonker to do the job, but that's better than not doing it at all.

Or are you offering to sell/ship us small quantities of the powder?

[Dan Schultz]

[quote="musician"]Slime Away is good stuff but much more corrosive. /quote]

I use Slime Away... because it IS good stuff. The basic ingredient in Slime Away is sulfamic acid... the same stuff brick masons and concrete finishers use to clean mortar off of brickwork and do exposed agragate (sp?) for sidewalks, etc. Local chemical companies sell bags of sulfamic acid crystals for cheap.... about $1 a pound. I mixes with water and the saturation limit is only about 10% by weight. You wouldn't want to take a bath is this stuff, but it's relatively harmless unless you breath a lot of the raw dust from the crystals. I still use rubber gloves. I've never known slime away or sulfamic acid to actually reduce the size of anything, but if you leave a horn submerged in sulfamic acid too long, it will leach the zinc out of the surface of the brass leaving a nice rose (copper) finish. Of course this has absolutely nothing to do with the original posters question about lapping valves!

[Chuck(G)]

....and yet we've had various folks on this forum rail against using CLR, whose main active ingredients are glycolic, sulfamic and citric acid.

Well, let's see...we already know about sulfamic fron Dan and Joe. Glycolic is an alpha-hydroxy acid used in skin care and as a general purpose cleaner where lime is involved, particularly in the dairy industry. It's also used in the cosmetics business.

And citirc acid is the primary active component of--lemon juice.

So Slime-away good, CLR bad?

I don't get it.

[Dan Schultz]

....and yet we've had various folks on this forum rail against using CLR, whose main active ingredients are glycolic, sulfamic and citric acid....... So Slime-away good, CLR bad? I don't get it.

Hmmmm.... I think it has ALL to do with HOW the chemistry is used. The old-timers used muriatic acid (as so do/did most radiator shops). Acid is acid. A horn left in vinegar too long is going to be a problem, too.

Most of the criticism towards various cleaning methods that I've seen on this forum has been directed at simply trying to be helpful.

I do my chemical-cleaning in a area where very little else is going on.... in two big poly tanks and a very handy and abundant water supply. I wear goggles, a rubber apron, and gauntlet style rubber gloves. I take a lot of care in how long things stay in the cleaning materials and take even more care insuring that all the materials are washed away afterward.

[Chuck(G)]

What would you use to lap slides? I have tried using pumice and rottenstone and they put a heck of a shine on your slides but the powder is much too fine to actually remove any of the metal.

Speaking from my own experience, I've found very few slides that actually need lapping, unless they're fresh from the plater's. As Joe S. has observed, most of what we view as "too-tight" slides are really dirty or misaligned.

I use #0000 steel wool to burnish slides (doesn't really remove any metal; it's way too fine). I then try each leg of the slide individually--if they don't bind, then any tightness is the result of not paying attention to alignment. Lapping misaligned slides will do more harm than good.