Lapping Lee Pro4-20 so it doesn't drip

[Bob58]

I've been asked about what I did to my Lee Pro 4-20 pot, so that it doesn't drip. Rather than reply individually to those who asked, I wanted to post a description of what I did, so that those more knowledgeable than I could read it, and comment if I did something wrong.

First, it's possible that I just got a Pro 4-20 that wouldn't have dripped anyway, had I done nothing to it. I didn't try the pot prior to lapping the metering rod, so I don't know.

Here's what I did.
1. Remove the screw, near the top of the metering rod. This screw allows adjustment of the flow rate.
2. I didn't clean the fitting at the bottom of the pot, where the metering rod fits, since my pot was brand new and didn't look like it had any use. But for a pot that has seen duty, the metering rod should probably be taken out, and the fitting where the metering rod sits should be cleaned as thoroughly as possible. You want to be lapping the fitting, not crud in the fitting where the metering rod sits.
3. I used lapping compount from Sinclair International's scope ring lapping kit. This is a fairly course abrasive (it's designed to allow rifle scope rings to be lapped into alignment with each other fairly rapidly.) I suspect that valve grinding compount, or something similar, would work also.
4. Place a small amount of lapping compound on the bottom of the metering rod, and drop the metering rod into the fitting where it normally sits.
5. Using a screwdriver, apply downward force on the metering rod, while turning the screwdriver (I turned in only one direction, so as to be sure to lap symmetrically.)
6. When the lap gets dirty and "broken down", clean the lapping compound residue off of the bottom of the metering rod, and out of the fitting where the metering rod sits.
7. Repeat steps 4 thru 7 "until done."
8. Clean all lapping residue, and reassemble (metering rod adjustment screw back in place.)

I lapped for probably 15 minutes total, before I "guessed" (hoped?) that enough lapping had been done. Apparently, thiswas enough, as after several sessions with the pot, it hasn't leaked, even once.

Again, I don't know if what I did, described in the above steps, was responsible for the pot not leaking.

If somebody has a better method, please feel free to post it here.

[snuffy]

Sounds like a good method. With my 4-20, I did nothing to it, it doesn't drip! The old production pot, on the other hand, has always dripped.:twisted: I always supected it was because the valve rod came in at an angle. Not one of Lee's better designs.

[44man]

I did mine the easy way---I took all the junk off and plugged the hole from the inside. Viola, no more drips. The ladle is my friend.

[Freightman]

Did that to my old Lyman Mold Master I am faster with a ladle

[Ricochet]

Simplest effective way to deal with the drip is to take the stick I whack the mould with to drop the boolits and whack the rod stright on top whenever it starts dripping.

[Cherokee]

Ricochet - After a while wacking the top of the rod, you will knock the spout out of the bottom and get a surprise flow of the silver stream. Been there, done that, don't do it anymore. YMMV

[Poygan]

My method is to attach a needle-nose vise grips to the top of the rod. Occasionally I need to turn it a bit but the extra weight seems to eliminate the majority of the dripping.

[Sundogg1911]

I do the "Whack the rod" trick as well. Turning it with a screwdriver helps the slight drip. I'm not beating the snot out of it, just a light tap to knock out what ever is stuck in there. I've also done it on the master caster pot, on the rare occasions that it drips.

[454PB]

I haven't done the lapping routine, but I do pull the rod every 1000 boolits or so and clean it. It's surprising how much sulphur looking oxides build up just above the point and cause poor valve seating. I suspect that is why whacking it occassionaly helps stop the drip.....it knocks this oxide off the metering rod. While the rod is out, I use a dental pick to scrape the inside of the spout.

[357maximum]

+1 for the lucky pro4 20 owners...never had an issue that was not self induced

[dragonrider]

Cherokee wrote:
"After a while wacking the top of the rod, you will knock the spout out of the bottom and get a surprise flow of the silver stream. Been there, done that, don't do it anymore."

Yup he's right, I did that to one of mine.