Fox 35 Backplate Gasket Leak

Stuka Stunt Main Forum · 17 of 17 known posts recovered

Larry F · Dec 13, 2000 08:32 PM

Gang --

The Fox 35 is still on the portable break-in plywood, and coming in nicely with about half a gallon of 29/5 through her.

She's got swimmer's ear, though. Looking at her from the back, she has a little bubble of pus that forms just above her left (from the back) ear on the backplate. I have removed and retightened the backplate twice. No sign of a boo on the backplate or the case.

One suggestion was to remove the backplate gasket and put in an O-ring. Whaddya think?

Larry F

Brett Buck · Dec 13, 2000 08:48 PM

#1 source

>She's got swimmer's ear, though. Looking
>at her from the back,
>she has a little bubble
>of pus that forms just
>above her left (from the
>back) ear on the backplate.
>I have removed and retightened
>the backplate twice. No sign
>of a boo on the
>backplate or the case.

Remove the backplate, and lap it flat on an Arkansas stone or 600 grit sandpaper. Clean it all off with acetone. Then re-assemble it with Permatex Ultra Copper automotive exhaust header sealant. Just snug it up, let it sit overnight, then tighten. You don't need the paper gasket.

Brett

Bigiron13 · Dec 13, 2000 08:48 PM

#2 source

I wouldn't try the "O" ring. If you have the stock backplate, the O ring won't seal because the backplate is so much less in diameter than the hole in the case. If you have the new Stuffer plate, the O ring will hold the plate so far from the case that you will likely bend the ears on the backplate before you get it tight. I would recommend replacing the backplate gasket. And while you have the backplate off, closely inspect the case for a scratch or gouge that would keep a new gasket from sealing. Clean ALL parts of the old gasket from both the case and the backplate before installing the new one.
Bigiron

Larry F · Dec 13, 2000 11:19 PM

#3 source

Brett and BigIron 12/13 notes:

I'll scrap the O-Ring idea. Listening to Gore and Bush tonight, I grabbed the plywood, brought it down here where we live, and took the backplate off. Lapped the back of the case with 600 on the plate glass on the back of the wet bar (the big, strong, handsome wife was too engrossed in politics to notice the castor oil fingerprints on the glass). A small gouge did show up after a few passes, which is probably the problem. It is shiny smooth now.

Now all I need is the Permatex.

Larry F

Larry F · Dec 13, 2000 11:28 PM

#4 source

Oh, yeah --

The previous hints on break-in work. Tilting the engine up and down on a plywood board does indeed show when it starts to take the break.

Only problem is the door. When the room gets too smoky, I grab the board, and open it with the engine running. Put my hand in the prop twice. It will be better in the summer.

Larry F

Bigiron13 · Dec 14, 2000 09:58 AM

#5 source

Larry, I have great respect for Bret Buck, but I would use a new gasket rather than the permatex. Unless. that is, you have the stuffer backplate. There is so much of the area of the stock backplate exposed to the INSIDE of the case around the flat surface where you would put the permatex that some of it (the permatex) will dissolve off into the engine while the engine is running and cause some gumming up of the engine. The stuffer plate doesn't have that exposed area and can be sealed with permatex or silicone sealer.
Bigiron

Larry F · Dec 14, 2000 03:16 PM

#6 source

Brett and BigIron --

We'll see. I did it all and will let it sit overnight. I wasn't happy with the lap job, and hand lapped the cover to the case with rubbing compound as an extra precaution. Removed the excess compound with acetone (some got in my thumb cut -- WOW!). Examined the old gasket with a magnifier, and decided to re-use it. Couldn't find a flaw. Troweled the thinnest of possible coats (razor blade and toothpick) on both the backplate and case, and screwed it back together with no external squeeze out, so presume no internal squeeze out. That approach should make all three of us happy.

We'll know the answer tomorrow evening.

Thanks

Larry F

LNeumann · Dec 14, 2000 04:32 PM

#7 source

For a lapping compound. good old Lava Soap works quite well. Scrape a little off with a knife, add just a small amount of water and stir until you get a thick liquid. Then apply to the back plate and rotate it against the back of the case to get a "perfect" fit. I fit a Fox 35 so well that way that I was able to bolt it back together without any gaskets whatsoever, and no leaks, either. I don't recommend that, however, as it brings the back plate closer to the shaft and on some engines there could be a lot of rod scraping in that area. But if you lap it, then put the gasket back in, any previous leaks should be gone.

Oh, yes, make sure you clean all parts (rinse in water) before reassembly. If you leave a little Lava Soap in the engine and try to run it that way, you could ruin the engine on that very first run.

Leonard Neumann

Larry F · Dec 14, 2000 04:44 PM

#8 source

Leonard --

Too late for this engine, at least this time. Done did it. Will remember for the future.

I did smear a little extra rubbing compound around the inside while I was in there. That should speed up the break-in, right?

Thanks,

Larry F

LNeumann · Dec 14, 2000 05:01 PM

#9 source

Actually Fox used to sell some stuff that was supposed to help speed up the break in process. You would mix a little with oil and dab it into the intake while the engine was running on the stand. Trouble is, they also sold some lapping compound that looked pretty similar. One dab of that in the intake while the engine was running and the whole thing could be toast. Maybe that's why they quit selling the stuff.

Leonard Neumann

Bigiron13 · Dec 14, 2000 05:21 PM

#10 source

LAST EDITED ON Dec-14-00 AT 06:03 PM (EST)

I still got some of the stuff. They called it Lustrox I believe. You could open up a brand new engine direct from the factory and the shaft and some nooks and crannies of the crank case would have the stuff in them. It aided in break-in, and also in wear-out.
I believe the material is Pumice and that is what is in the Lava soap isn't it Leonard?
Bigiron

Garf · Dec 16, 2000 12:05 AM

#13 source

Lustrox was supposed to be Garnet powder from what I can remember.

"SAVE ALL THE PIECES"-Phil Brown

Jim T. · Dec 16, 2000 08:22 AM

#15 source

"The older I get the better my Foxes used to run." Back in the 70's I bought four on sale for $12.95 at one of the discount houses (unfortunately that one didn't last) and took up flying stunt. I lapped them all in with Dupont white as GARF says. All four ran exactly the same. I ran in a rich 2-cycle with a Zinger wide 11 x 5 on 540 square, 48 and 42 oz airplanes. Several times at contests people who did not know me asked if I were running an ST 46, and were amazed when I turned the airplane over and showed them the Fox. I remember it well.

Jim Thomerson

Larry F · Dec 14, 2000 06:37 PM

#11 source

>I did smear a little extra
>rubbing compound around the inside
>while I was in there.
>That should speed up the
>break-in, right?

Naah! I was just jacking Leonard around a little. I have no intent of speeding up the break-in, and would not put anything in the engine except for fuel.

By the way, breaking in an engine at night is quite informative. Little meteorites come out of the exhaust that you never see in daylight. Maybe it is fully broken in when they stop coming out? I am serious now, and not jacking anyone around.

The stock Fox muffler works quite well. It makes the engine hardly any louder than with no muffler.

Larry F

Garf · Dec 16, 2000 12:10 AM

#14 source

I use DuPont #7 white polishing compound to lap my Fox Stunt piston & cyllinder assy. works great.

"SAVE ALL THE PIECES"-Phil Brown

jerry · Dec 15, 2000 07:27 PM

#12 source

LAVA SOAP.....good thing us old timers are still around,we always packed a bar of lava in the tool box in the early racing days,34 fords and flathead engines.if you got a leak in the gas tank just rub on the lava bar and it would stop!great for lapping valves and if you spotted a cute girl in the grandstands YOU COULD EVEN WASH YOUR HANDS WITH IT!,ah yes....great stuff,...to seat the rings in the flatheads we would blow about a 1/2tsp bon amie in the sparkplug hole...bet most kids today would not what a flathead ford even looks like,...back to the topic of sealants!omit the word permatex!we are talking high temp silocone,as a rule its orange...at one time we could not keep the header gaskets from leaking on our chev powered sprint cars.went to the hi temp silicone and NO gaskets....problem solved,i recently went through a minor rebuild on several old mccoy engines,i left the old gaskets and with a toothpick put just a slight but consistnt film of the h.t.s.around the head and sleeve gaskets,ive flown them quite a bit since with no problem....sure enjoy the forems,thanks to all for your help..old but new,jerry

Larry F · Dec 16, 2000 11:15 AM

#16 source

A Thank-You Note--

Hi! I am Larry's Fox 35, and I appreciate your concerns for my health. Well, thanks to your kind cards and letters, I am totally cured now! Larry tried to take care of me when I was sick, but he didn't know quite what to do.

Larry and I are looking forward to a long and happy relationship now that our problems are behind us. He hasn't seen what I can really do when I am off this bench and on the front of a real airplane. I can't wait!

(Hope you can read this OK -- I am typing with a Bolly prop)

Little Lady Fox 35