tapping a back plate

[Billy Fields]

Is it possible to tap a fitting into the back plate for pressure for the tank on a old McCoy 35.

[Dave Hull]

It can certainly be done. If you have yours apart (I don't have one in front of me right now) look at the upper left backplate screw hole. It should be into meat on the case near the bypass. You may have to drill/tap all the way thru. Then you install a fitting that has the propoer thread and a hex flange and a nipple. Functions as both a backplate bolt and a case pressure tap. My next choice would be to JB weld a boss in the center of the backplate and drill and tap that.

But the real question is why use a pressure tap on a Mickey 35....

[Billy Fields]

It can certainly be done. If you have yours apart (I don't have one in front of me right now) look at the upper left backplate screw hole. It should be into meat on the case near the bypass. You may have to drill/tap all the way thru. Then you install a fitting that has the propoer thread and a hex flange and a nipple. Functions as both a backplate bolt and a case pressure tap. My next choice would be to JB weld a boss in the center of the backplate and drill and tap that.

But the real question is why use a pressure tap on a Mickey 35....

I have that engine on a combat wing with a clunk tank. when inverted it stops running. I could use a bladder but I have no idea on how to make one. I guess I could get one of the guys at the field to make me one or get a tongue muffler with a nipple on it. Just seeing if that way is a option mainly.

[Dave Hull]

Sir William,

Based on just your brief comments, I would look at the tank and plumbing again before adding pressure. It is my thought that it should run fine inverted without pressure. They do in stunt planes, and unless you have opened up the venturi, it should in a "combat plane" too.

Does it quit lean when you go inverted?

Divot McSlow

[Cody bishop]

I have that engine on a combat wing with a clunk tank. when inverted it stops running. I could use a bladder but I have no idea on how to make one. I guess I could get one of the guys at the field to make me one or get a tongue muffler with a nipple on it. Just seeing if that way is a option mainly.

Making a bladder tank is simply buy the tubing, bladder connectors, bladder end plugs from MB’s model supply and wrap the ends in floral wire and twist the as tight as you can without breaking the wire then fit the wire as short as possible and bend over the tale you will also need a bladder compartment use a peice of the floresent tube protectors about 6” long drill a 1/2 hole near one end to alow bladder removal epoxy 3/32 balsa on each end

[Dan McEntee]

I have that engine on a combat wing with a clunk tank. when inverted it stops running. I could use a bladder but I have no idea on how to make one. I guess I could get one of the guys at the field to make me one or get a tongue muffler with a nipple on it. Just seeing if that way is a option mainly.

   YES, by all means check your tank. If all is correct, it should run as well inverted as upright. Clunk tanks are easy to rig, but also easy to accidentally foul up. There is an old thread in the engine section on how a guy hand made a muffler for a McCoy .35 out of sheet metal that looks promising. If you think you can duplicate that, add a pressure fitting to the muffler, it will easier and less to go wrong. Or find one of the old DuBro clamp on mufflers. They are heavy but will suit your purpose.
  Type at you later,
   Dan McEntee

[Steve Helmick]

I'd wonder if the clunk line (pickup) wasn't stuck under one of the other tubes. Seems the most likely.

I am NOT a fan of Sullivan tanks. The DuBro, Hayes and some of the others are simpler to assemble and much less likely to leak...critical if you are going to use muffler or crankcase pressure. But still important, even if not using pressure.  Steve

[john e. holliday]

If you are running uni-flow tanks I have discovered by use they won't work on a combat plane.  Have since converted tanks to single vent line with over flow capped off.   I have four combat wings the uni-flow won't work.   Now if you browse the combat section I think there is a diagram on making bladder tanks.   But if you really want to try the McCoy check back plate screws and see if one of them is open all the way into the crank case.   Then find a nipple that will fit.  Then you have the fun of starting it with out flooding the engine.   

[Billy Fields]

OK guys thanks for all the help. I flew it today and it would go for about 3 laps then quit. I brought it home and found a old dubro muffler that I cut down for a boat and put it on the engine with pressure to the tank and now it run great no matter how I turn the plane so I think my problem is solved. Thanks

[Ken Culbertson]

If I remember right the backplate screw on the top (intake side) goes through.  We used McCoy's for combat when I was in the service.  It was all we could get through the BX.  They are not really designed for crankcase pressure and it took us a while to figure out how to start them without flooding (ended up pinching the pressure line then slowly letting it lose after it started).  Sort of like you do with a bladder.  Be respectful, McCoys were good engines for a great price but they really don't like to run at combat RPM's for very long.  Another thing we found out was the stock NVA was super sensitive on pressure.

Good Luck - Ken

[kevin king]

I tried taping a pressure fitting to a backplate many times but the tape wouldn't stick.