Shielded plugs

[Carrieve]

Hi gang. I need to close the cowl. I bought the Champion RE37BY plugs with new right angle shielded leads thinking they would clear the cowl. No way. I just hate to cut and install the bumps. The engine is the -12 85hp with the old Eisenman mags. Anybody have any suggestions? I had the new leads made up by Aircraft Spruce and they stick up about 1/2 inch too much.

[lawheelock]

Re: Shielded plugs

You may have to live with bumps. The later T-crafts with shielded ignition have them.
There was an article or message a long time back, I think it was on this site, about adapting some shield cups used on Ercoupes years ago that were supposed to be available from Fresno Airparts.
When I get my present Tcraft back in the air it will have the bumps.
My hearing is nearly gone now primarily because of a 1000 mile trip in about 1966 in my original BC12D that had unshielded Eismanns, wires, and plugs and I had a wind generator and a Superhomer that I listened to with old fashioned suplus headphones the whole trip to keep the VOR tuned. The ignition noise pretty much destroyed my high frequency hearing. I would gladly trade bumps and shielded ignition today if it would have prevented my hearing damage.
Larry Wheelock, 1946 BC12D from '64 to '69 N96927, now restoring N96179

[paulnuss]

Re: Shielded plugs

I had Eisemann mags on my '46 BC12-D1, but the radio noise made a hand-held radio unuseable. I operate in a radio environment often, with two common destinations having class D airspace, and my home field with turbine and other traffic that come in fast, and others who don't look outside the cockpit. I was unable to obtain a shielded harness for these mags anywhere. I also, like you, didn't want bumps in my cowling. I bought new Slick mags with shielded harness, plus "Ercoupe" cups. These allow a shielded ignition lead set without cowl bumps; the harness attaches to the cups at a 90 degree angle, clearing the low cowling. The regular shielded plugs are used on the bottom, lots of room without interference there. You might get away with only two of the cups on top, for the front plugs; check that out. Instead of regular shielded plugs, I use M-41 unshielded plugs in the top. The shielded harness wires' "cigarette" attaches to the cups, with the connecting wire spring protruding thru to touch the top brass bulb of the M-41's. The shielding is good, with a minimum of ignition noise. Don't forget to shield your p-leads too, they often are a major source of noise. Some machining was necessary on the "Ercoupe" cups, to re-thread the attachments for the Slick harness, and also at the bottom to fit the plug holes and plugs. "If only" they would make a bit shorter shielded plug, this wouldn't be necessary, but I never found one short enough.

[Carrieve]

Re: Shielded plugs

Thanks for the help. I checked with Champion at AirVenture for a shorter plug but nothing available. I already have a brand new harness from Aircraft Spruce so I will probably go with the bumps. Darn. Darn.
Paul did you have to buy the new gears when you went with the Slicks? I heard you have too. Money is short or I would have gone the Slick route. I just bought a Pitts, built a new hangar and on and on it goes. A giant sucking sound on my retirement.

[paulnuss]

Re: Shielded plugs

I didn't have to change the gears. I wasn't able to come up with any kind of shielded harness for my Eisemanns though. And the coils were becoming weak when hot, and I read that the replacement coils for Eisemann mags were old stock, manufactured many years ago, and were often not much good anyway, so I bit the bullet and bought the Slick kit. I am finishing up a many-years rebuild of my 1974 Pitts S2A, Mattituck overhauled the AEIO-360-A1A with new crankshaft to replace the AD'd light flange ($$$$$), and overhauled Hartzell constant-speed prop with new "B" hub ($$$$$), new fabric and paint plus some minor wing repairs (more $$$$). If God had intended for Man to fly, he would have given him MORE MONEY!

[Ron Coleman]

Re: Shielded plugs

About shielded plugs.
the Ercoupe cups are pretty simple to make. They are only a can turned out of aluminum with a threaded lid. There is a nipple welded into the side of the can with a thread that will allow a harness to screw onto the nipple. The ignition wire, cigarette and contact spring goes through the nipple to contact the plug. The cups come in various sizes and configurations. One type has a thick cap with a deep thread. This type has a dome turned into the cap to distance the cap from the plug to help prevent spark over. Some of the cups use a thin cap without the dome. The cups come in various heights, I suppose it doesn't make any difference as long as it clears the cowl and doesn't short the plug. Some of the caps have a lug swedged into the top of the lid. the lug has a hole in for a safety wire. I take the lugs off because its makes the cups too high and they rub the cowl. Instead I drill a small hole in the rim of the cap and run the safety through that hole. A slot is cut in the top of the cap so that the cap can be tightened with a flat bladed tool. If the cap is not tight and rattles around it will result in radio noise. Lots of noise.

The bottom of the cup is turned smooth and is the same thickness as a standard plug washer (gasket). The cup serves as the gasket. Do not use the copper washer with the cup.

lWhen I ordered my slick mag set from Unison I told them what I was doing and they sent me a set of mags with gears (to be installed) an extra set of plugs and a harness that matched my lower shielded plugs and my upper set of cups. When I tried to thread my harness on to the cups I found that the nipples were not threaded on to the nipples far enough. I bought a die ( $35.00) and corrected the problem.

I would not screw up my cowling with those ugly bumps (unless they went all the way around like on a Waco) when I could solve the problem with a couple of Ercoupe cups.

RonC

[dewhitaker]

Re: Shielded plugs

Here are some pics of the shielding cups. I have well over 300 hours flying with this arrangement on C-26 plugs on top. No issues and the handheld radio works fine. Slick mags were installed at the time I did this.

Just this week I have installed the new M-41 plugs in the front cups and have elected to put 37BY short shielded plugs on the rear. They will just make it under the cowling.

Please remember that every cowling will fit a little different, what may work for one may not work for another.

[waltermrich]

Re: Shielded plugs

Just wondering did you get your cups from Fresno Air in California

[paulnuss]

Re: Shielded plugs

I for one got mine from Fresno.

[NY86]

Re: Shielded plugs

My experience is that some Eisemann mags are installed with odd-ball gears and some aren't. I have not found rhyme or reason to it, though.

Right angle harnesses take up more space than straight ones pulled to a right angle. You may be able to get the 1/2" you need that way.

[Carrieve]

Re: Shielded plugs

Thanks gang for all the help. I need to go and get some measurements as to clearance and then go from there. I will keep all posted as how things work out. I am sure this is a problem for all of us who want to keep our cowl "clean".