Seized fox 35 engine

[Allenayres]

I had an old control line plane given to me and it had a fox 35 40th anniversary engine on it. When I got it I couldn't get the propeller to turn at all. I took the head and back plate off along with the propeller and soaked it in kerosene for a couple of days. It turns over now but it seems a little stiff. However, I really have no reference to what stiff is so I don't know if it's still gummed up or if it just has good compression. How can I tell if this engine is worth buying fuel for and spending the time to get it going?

[Brett Buck]

I had an old control line plane given to me and it had a fox 35 40th anniversary engine on it. When I got it I couldn't get the propeller to turn at all. I took the head and back plate off along with the propeller and soaked it in kerosene for a couple of days. It turns over now but it seems a little stiff. However, I really have no reference to what stiff is so I don't know if it's still gummed up or if it just has good compression. How can I tell if this engine is worth buying fuel for and spending the time to get it going?

     It needs to be thoroughly cleaned before you have much idea. At least, remove the backplate and glow plug, and slosh fuel around in it for a while. If that doesn't loosen it up after a few minutes, switch to lacquer thinner. If that still doesn't work, then disassemble it completely and antifreeze/crock-pot the engine. Be careful with the circlips, those are hard to find not that Fox is out of the engine business. Once clean, reassemble with light oil (Marvel Air Tool oil or 0-40 motor oil), then check.
 
   Generally it should feel very "flippy" and rock back and forth a few times when it comes off compression. If it doesn't feel that way, it might be damaged (like from a crash, bent crankshaft or distorted case). An experienced modeler should be able to tell the difference between too tight in the piston/cylinder and the bearing/crankshaft.

      Brett

[kenneth cook]

              A heat gun will free the engine up which is frozen most likely due to castor oil solidifying. Concentrate on the conrod and make certain it's not frozen on the wrist pin. Heat gun, gloves,  penetrating oil and a allen key is what your going to need to free it up. Spray the penetrating oil into the underside of the piston holding it upside down. Heat the top of the rod with the heat gun obviously holding the engine with gloves and heat until the oil is beginning to smoke. You should be able to get the allen key behind the rod and carefully pry it away from the crank web. Push it back in and repeat this process several times until it's freely sliding. Taking apart the Fox can be a bit troublesome if your not familiar with doing so. Nothing indexes the cylinder so it's critical to mark the cylinder to the case with a witness mark prior to taking it apart. Many times the sleeve goes back in and the installer not knowing puts it in backwards. The cork backplate gasket is more than likely going to be need of replacement and these are becoming a bit more difficult to source due to Fox exiting their engine manufacturing. Permatex makes a product anaerobic gasket maker and it comes in a very small tube about 1.5 " long which costs less than $7. It works terrific for this application and there's enough in there to last a long time afterwards . Unlike RTV, this material doesn't harden in the tube and has good shelf life.

           I've found the 40th anniversary case Fox's to work very well aside from the muffler ears which are extremely fragile. If you can source a gasket kit, you will receive allen cap screws for the entire engine (minus the muffler attachment screws) , a case gasket and a head gasket. Brett's comment are very correct and the circlips as he suggests deserve a lot of attention if the engine needs to be fully dismantled. I personally would avoid the area all together. Even twisting the wrist pin within the piston can cause the circlip to disengage. When this clip departs, it typically happens when the engine is running. To avoid incident, I would not take these out or even play with it unless it's absolutely needed and if your not familiar with it's construction.

[Jim Roselle]

I have a Fox .35 that I was able to purchase for $5 because it was seized. I submersed it in fuel for a week, cleaned with a rag, mounted it on a model and went flying. Runs great, just saying.

Jim

[Ara Dedekian]

          Allen

             I just freed up a bunch of engines, including two Foxes, that were stuck so tight I needed a torch to soften the goo enough to get the parts moving for disassembly. Carefully torching also speeds up the process condiderably; 1/2 hour to an hour to completion. I'd go through Brett and Ken's replies a few times as they're spot on. I too avoid removing the clips but if you do, make sure the grooves they sit in are cleaned out. But I have successfully formed new ones out of the same diameter wire.

             Also, I've replaced the cork gasket with a .007" hard paper one. (the invoice from the oil burner fuel delivery). If paper is good enough for Supertigre backplates, it should be good enough for Fox. Just stick a piece on the open crankcase, cut out the inside with a new blade, reattach the backplate and cut away the excess. Now you have a fully formed gasket, not just a ring.

         Ara

[George Albo]

If you don't know how to make your own gaskets, go here: http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313.TR0.TRC0.H0.Xfox+35+gaskets.TRS0&_nkw=fox+35+gaskets&_sacat=0

[Dave_Trible]

I've had pretty good results using aluminum foil duct tape for gaskets.  Once done run the engine a little to get warm then tweak the bolts a little tighter and you should be good to go.  I soak stuck engines in lacquer thinner for a while which gets most things moving and a heat gun will usually finish the job.  Be careful though about the wrist pin.  It can still be stuck to the rod but turn in the piston.  It will start up and run this way for a short time then ruin itself and sort of melt down on the test stand.  It was an old Fox on which I learned that one.

Dave

[Allenayres]

Thanks for all the input. This has definitely given me a few things to try out. I'm sure Ill be back with more questions as I try to get this thing up and going.

[Howard Rush]

Had Fox started pinching the cylinder at the top when he made these?

[Allenayres]

So here is an update......I let the engine soak in acetone for about 20 minutes. When I got it out, I could turn in over with my hand on the crankshaft. I made sure all the acetone was dried out and then I got a little oil on my finger and wiped it over everything I could reach. While I was putting everything back together, I noticed that at the top of the stroke there was a little bit of of play before the crankshaft engaged the con rod again. This may be normal as the motor turns but it did not seem as fluid of a movement as I thought it would. Anyway I put everything back together and tried turning it over again. It turns over just fine but as i try to spin the propeller with a rod it doesnt act like I thought it would. I thought it would give me a little more flipping action than it does. I put a link to a video for yall to watch to see what I am describing. The problem is I really dont know what to expect because I have zero experience and no one around me knows anything about these engines either. So what do yall think? Is this motor worth moving forward with?

Video link: https://www.youtube.com/watch?v=6ZN4VGdgRoA&feature=youtu.be

[Steve Helmick]

Looks "dry". Some decent glow fuel might make it run, but getting decent glow fuel is often a hassle these days. You'd want 5% to 15% nitro with 25% castor oil...the later is the problem, generally. If we don't know roughly where you are, it's tough to be very helpful with this.

Soaking the whole engine in kerosene is a good start. Often the worst problem is the top end of the connecting rod is seized to the wristpin with castor oil glop. The crankpin isn't usually a problem. The Fox rod is usually pretty loose on the crankpin, and while they are certainly available on eBay, be aware that the Fox company no longer makes model engines and doesn't seem to want to sell parts, even if they have them in stock.    Steve

[Brett Buck]

So here is an update......I let the engine soak in acetone for about 20 minutes. When I got it out, I could turn in over with my hand on the crankshaft. I made sure all the acetone was dried out and then I got a little oil on my finger and wiped it over everything I could reach. While I was putting everything back together, I noticed that at the top of the stroke there was a little bit of of play before the crankshaft engaged the con rod again. This may be normal as the motor turns but it did not seem as fluid of a movement as I thought it would. Anyway I put everything back together and tried turning it over again. It turns over just fine but as i try to spin the propeller with a rod it doesnt act like I thought it would. I thought it would give me a little more flipping action than it does. I put a link to a video for yall to watch to see what I am describing. The problem is I really dont know what to expect because I have zero experience and no one around me knows anything about these engines either. So what do yall think? Is this motor worth moving forward with?

Video link: https://www.youtube.com/watch?v=6ZN4VGdgRoA&feature=youtu.be

   Slosh some fuel around inside as previously noted, then see. rubbing oil on the exposed surfaces without disassembling it won't really help too much, you need to get oil all over inside.

     Brett

[Allenayres]

Ok so my next step is buying fuel. I live in NW Louisiana and the only place I can find anything close to what I need has something that says 10% airplane fuel ( which I assume is nitro) and 18% castor/synthetic. Would this be ok to use if I buy extra castor oil to add in to bring that 18% to 29%?

[Tim Wescott]

Ok so my next step is buying fuel. I live in NW Louisiana and the only place I can find anything close to what I need has something that says 10% airplane fuel ( which I assume is nitro) and 18% castor/synthetic. Would this be ok to use if I buy extra castor oil to add in to bring that 18% to 29%?

If you've been soaking that thing in acetone you might want to put some oil in it and flip it through a bit NOW.  Particularly if it's humid there.  Keep it rust-free until you run some castor through it.  After-run engine oil is best (which you can get at your hobby shop, hopefully).  Some castor oil (you can get it in little bottles from the drug store) is probably second best.  Automatic transmission fluid or sewing machine oil is probably third best (I'm guessing).

I wouldn't mess around with the fuel -- mail-order a quart of Sig 10% nitro, 25% castor.

[Air Ministry .]

Really think youd benifit from stripping it , and if neccessary CLEANING the Insides . Use a green 3m dish scourer thing .

Both the engines im mucking with ( or were they mucking me ) were corroded from poor storage . a Como 51 & a FP 40 .

The gudgeon / wrist pin is probably the most vulnerable .

The Como just needed degunking and the wrist pin scouring clean , and is transformed . Hope the FP 40 is the same .
Had ' oxidation over the non working areas of the crank , and maybe the goop was transfering / lacquering up the
rest when running . Itd improved a bit with syntetic oil , then went hopeless again .

So at least take of the backplate and look to see if it looks clean enough to eat your dinner off . Before Running .

[Brett Buck]

If you've been soaking that thing in acetone you might want to put some oil in it and flip it through a bit NOW.  Particularly if it's humid there.  Keep it rust-free until you run some castor through it.  After-run engine oil is best (which you can get at your hobby shop, hopefully).  Some castor oil (you can get it in little bottles from the drug store) is probably second best.  Automatic transmission fluid or sewing machine oil is probably third best (I'm guessing).

I wouldn't mess around with the fuel -- mail-order a quart of Sig 10% nitro, 25% castor.

   I wouldn't wait around for fuel. Since you have some kerosense, dribble some of that in the venturi and exhaust, remove the glow plug, and slosh THAT around, get as much out as you can, then use any household oil in the venturi and exhaust, and flip it a bunch of times. Kerosene has some value as a lubricant and will ensure at least something gets on the wrist pin, which is the likely danger area. It should then feel pretty flippy and free.

   BTW, be a little careful with the engine when it has a lot of free acetone and kerosene in it and the glow plug in. There's a very remote possibility that even without a battery attached, it will "pop" and fire a rev or two. It won't keep running but don't get too casual.

    Something with some lubrication and protective value needs to be sloshed around *now* to avoid allowing it to either gum up or rust up. I suspect that, after having seen the video, that the only thing wrong with it is that it needs to be lubed and then run. DO NOT completely disassemble it because with it freed up enough to flip, its freed up enough to check for a bent crank. Unnecessary disassembly can only cause problems. Foxes are fine running with a lot gummed-up old castor oil in them, that't what happens between every flying session anyway.

    You do need real fuel. I see no problem taking a gallon of Omega or similar 10%, pouring out half a pint,  and adding 12 or so ounces of SIG or Powermaster castor oil and running it. As long as you do not let it get too lean too soon, there's little chance of other permanent damage. 

    Brett

[Jim Roselle]

Check with a motorcycle shop, they may have klotz racing castor you can add to glow fuel.

[Gerald Arana]

Had Fox started pinching the cylinder at the top when he made these?

Howard,

Don't know about that but, I've pinched a few bottoms in my day! 

GA

[Dan McEntee]

   Now that you have it loosened up a bit, a shot of PB-Blaster in the exhaust and venturi will help finish up getting things "Flippy." Like the other guys said, getting something slippery all around the engine now will have benefits. I have found PB-Blaster to be quite good at lubing old engines. it cuts through gunk pretty well. My standard routine with barn fresh old engines, if they don't look too bad, is to heat them with a monokote heat gun for quite q while. Normal castor gunk will start to melt pretty quickly, and once you can turn the engine over with a prop, I give it a shot of PB-Blaster to help finish the job. It clings to the parts well and doesn't get gummy with age.
   This works about 99% of the time. I just got two old Fox combat engines last night that were stuck. The gunk looked blackish, like tar. The heat gun trick wasn't working so into the crock pot they went. After soaking on low heat for 24 hours (low heat does get pretty hot!) I pulled them out. They were clean as a whistle, but they still wouldn't turn over. I couldn't see any scoring or scratches in the cylinder, thinking that they might really be seized, but I have never seen a model engine get a piston to seize on a cylinder wall. I finally had to resort to gently heating the cylinders with a propane torch! That finally got that gunk to break down and let the pistons move. Then the PB-Blaster did it's job. I cleaned out a bunch of kibbles and bits of balled up gunk, then re-assembled it. They go "flippidy flippidy" really nicely now! There muct have been some sort of secret sauce oil in the fuel that these engines were fed. It wasn't normal castor oil. I had two Cox .049's out of identical P-40 plastic RTF planes that were stuck one time. Sometimes you can just heat a Cox engine really gently with the heat gun and they loosen up, then flush with fuel. These didn't respond to that treatment. I pulled them apart and found the tanks and crank cases filled with some sort of grayish sludge, almost like modeling clay. The tanks were filled with it! That couldn't have been castor sludge. it cleaned out but was difficult. They went back together and ran fine. Just another times where i wonder just what in the H-E double toothpicks some people tried to run in these things! And don't be surprised if your engine isn't fully broken in. Lots of these old engines we find are pretty low time. Just because they looked like they were run, doesn't mean that they were run very much.Given a few as we control line flyers are, I think we fly way more that a lot of our predecessors did and know a lot more about what under the cowling now.
   Type at you later,
   Dan McEntee
 

[Air Ministry .]

Check with a motorcycle shop, they may have klotz racing castor you can add to glow fuel.

Motul 2 T is supposed to be good , a Ace Here recomends for the Yatsenko , and the Euro types too . A trifle expensive its said .

[Allenayres]

Got everything together and got to try it out today. I bought some fuel from brodak. I backed out the needle valve about 5 turns and squirted a little fuel in the carb. It would busy off but once it burned off what I squirted in the carb it would die. Any suggestions on what to try to get it to run?

[Dan McEntee]

Got everything together and got to try it out today. I bought some fuel from brodak. I backed out the needle valve about 5 turns and squirted a little fuel in the carb. It would busy off but once it burned off what I squirted in the carb it would die. Any suggestions on what to try to get it to run?

    5 turns isn't open enough. Close the needle, and then open it and count the turns until it comes out. Should be about 10 turns. Original Fox needles have a pretty course thread. Put the fuel tubing on it like it has been mentioned, and put it back in and turn it in about 3 turns from fully open, and then try starting it. It will probably be close or a little rich, depending on the needle it has. Original Fox needles were not turned to a point, but had a flat taper on one side. In later years they started to turn them to a point but I think the spray bars stayed the same. Check out your needle to see what you have just so you'll know.  Lots of people have some experience with Cox or some other kind of engine that 3 to 4 turns open is normal for, so they think Fox .35 is the same. Let us know how it goes.
   Type at you later,
    Dan McEntee