Author Topic: Fox 35 Help! (Read 3971 times)

Alex Givan · « **on:** February 23, 2010, 05:31:02 PM »

My favorite FOX 35 has a problem that I can't figure out.

This engine for the last four or five months has been on a Flitestreak and running great, flying stunt an occasional informal combat match and even a little racing just for fun. During all this I have used Sig 5/25 with a little extra Castor added in, a 4oz uniflow tank, 10/6 APC prop and various plugs that all seem to work fine.
This is an older FOX that has the squared off exhaust, no muffler lugs or any material at the center of the exhaust port. On the bypass side FOX and "35" are raised letters and numbers. the original needle valve was the flat spot or blade type along with the valve body having two holes.

On the last couple of flights before things went bad I noticed a lot of black goo that seemed to come from the lower part of the back plate.
I operated the engine like this for at least a dozen flights with no problem until it started running ruff and lost power. My feeling at the time was that the back plate gasket had failed and caused the problem. This was replaced along with a new head gasket and put back in the airplane. No luck, the engine now will only run for a short time sputter then die.
I have done all that I can think of

1) Five different glow plugs, 2) Three different fuel tanks, 3) New needle valve assembly and fuel line, 4) Fresh FOX 10/20 fuel with extra Castor added. All of this has not helped at all, compression is good, tanks O.K. and the glow plugs are hot but the engine will not stay running for longer that 20 seconds or so. Any ideas other that an 0.S.25 ? $:-\$

dennis lipsett · « **Reply #1 on:** February 23, 2010, 05:42:58 PM »

Black goo is usually the result of running too hot or something is rubbing and shedding particles of metal into the fuel. It's time to look deeper into the engine and see what it is. It could be simply that the engine is coaked up from too much castor and you have a varnished cylinder. The cylinder will feel all right when it's warm but really stiff when cold.
Others more worldly on the Fox will chime in and give more useful advise.
dennis

Paul Taylor · « **Reply #2 on:** February 23, 2010, 06:05:06 PM »

Big Iron

Marvin Denny · « **Reply #3 on:** February 23, 2010, 06:19:33 PM »

As Dennis said--- tbe black goo can't be good. Black goo is almost always an indicati9on that something is eatign itsself up. most of the time it is aluminum. When you took the engine out of the plane to change the backplate gasket, was there any black goo up under the crankshaft front end area? I am thinking along the lines of oil flow out the front bearing area.
Where are you located? Are you close to someone that regularly does engine rework. If so they could probably tell you in an instant.
If you send me the engine I will tell you what I find and offer you a repair cost estimate. I have all the parts needed to do repairs on that engine.
My off hand guess from what you have said though is a galled shaft to case or a galled rod to crank pin. Either way, you will probably need some new parts.

Bigiron

Scott B. Riese · « **Reply #4 on:** February 23, 2010, 09:14:54 PM »

Two things.....Wrist pin stuck. OR...is the crank hitting the backplate??.

RandySmith · « **Reply #5 on:** February 23, 2010, 09:44:14 PM »

Alex

If it is lost power and will not run correctly,you have problems and really need to have someone look at it for you, Or you could ship it back to FOX

Regards
Randy

John_Craig · « **Reply #6 on:** February 24, 2010, 07:45:46 AM »

With soapy water check to see that you have no leaks (bubbles) around the head & backplate. I have heard of people having trouble with varnish from all Castor fuel when an engine is run hard. As the engine heats up the friction increases & the engine sags or stops. Steel wool the cylinder & piston, OOOO steel wool. Clean well & put the engine back together, also double check the proper position of the hole on the spray bar in the venture. If this does not solve the problem then call Fox, $50.00,+ shipping & your old engine gets you a new one.

Another way would be to clean the complete engine. Take it apart, mark the connecting rod for orientation & also observe the orientation of the cylinder exhaust Vs intake. In a small pot, cover all the parts with water, add 2T of cascade dish washer soap & boil for 20 minutes, brush off all the brown with a toothbrush, rinse well, oil & reassemble your engine, check for leaks.

Tom Niebuhr · « **Reply #7 on:** February 24, 2010, 08:19:52 AM »

Big Iron's words on Fox engines, is like taking gold bars to the bank. I highly recommend that Marvin look at your engine.

john e. holliday · « **Reply #8 on:** February 24, 2010, 09:29:35 AM »

I am on Tom's side, send the engine to Marvin. He will do you right and tell you have to prevent it next time.

Bill Little · « **Reply #9 on:** February 24, 2010, 09:35:16 AM »

With out a doubt, send it to Marvin! Something has gone kaput in there.

Randy Smith can also fix her up.

Big Bear

Garf · « **Reply #10 on:** February 24, 2010, 02:00:28 PM »

No one is in a better position to deal with a Fox than Marvin.

Richard Entwhistle 823412 · « **Reply #11 on:** February 24, 2010, 04:24:14 PM »

This isn't rocket science. Maybe to get the "perfect Fox run" it would be but to get it to run like it did in the past weeks should be a walk in the park. The bad gasket and most likely loose back plate was the reason for the "black gunk". Also loose mounting bolts produce lots of black down low on the motor. At my auto repair shop when a car came in with a leak, miss, noise or vibration and after we "repaired it" and then it wouldn't run at all or ran really badly the question was "What did WE do to it". In the thirty years I worked at auto motor repair 99.9% of the time the problem was something we did while repairing the first problem. So, when the head was off your motor during piston cleaning did you somehow rotate the liner? If you had the piston out the liner had to be out so could you have put it back in 180 deg. out? If you had the piston out is it back in correctly with the fence toward the engine block port? Look for something you did incorrectly while the motor was apart. Been there, done that and bought the "T" shirt.

Later
Richard

Marvin Denny · « **Reply #12 on:** February 24, 2010, 04:43:04 PM »

  Richard, I didn't see where he took the piston out--- only the head off. I would think that since he suspected a blown backplate gasket, he would have noticed a loose backplate. You are right in that loose (even a very little bit) motor mount will cause the black goo. I let that one slip by me. And since he took the head off it could be that he now has a head gasket leak . He should now check for a leaky head gasket by putting some soapy water around the head gasket area and turning the engine over slowly and look for bubbling.
  Another way is to invert the engine and place just the head area into a glass of water and turn the engine over and look for bubbles.

  Thanks for prodding my memory.

  Bigiron

Marvin Denny · « **Reply #13 on:** February 24, 2010, 07:04:14 PM »

Alex do you have a spare rod? If not, I probably have one in the junk barrel that you can have.

Bigiron

Garf · « **Reply #14 on:** February 24, 2010, 07:32:25 PM »

I have some fibre washers that will seal up the NVA. Let me know if you want a pair.

Richard Entwhistle 823412 · « **Reply #15 on:** February 24, 2010, 07:59:30 PM »

I have 20 plus brand new 35 rods I got in a ton of Fox parts I bought off EBay 6 years ago. Send me your address and I'll send you a new rod and a new pin free. Watch out for the little pin clips. They do get away in a heart beat! Someone may post what the fool proof method is to change a pin without the clips doing an escape to another universe.

Later
Richard

dennis lipsett · « **Reply #16 on:** February 24, 2010, 08:32:32 PM »

Quote from: Richard Entwhistle 823412 on February 24, 2010, 07:59:30 PM

I have 20 plus brand new 35 rods I got in a ton of Fox parts I bought off EBay 6 years ago. Send me your address and I'll send you a new rod and a new pin free. Watch out for the little pin clips. They do get away in a heart beat! Someone may post what the fool proof method is to change a pin without the clips doing an escape to another universe.

Later
Richard

I always remove those clips inside a gallon sized plastic baggie. So far I havent lost any in years. Knock on wood.
Dennis

Scott B. Riese · « **Reply #17 on:** February 24, 2010, 09:01:11 PM »

Richard...If your going to take off the wrist pit clips...do it inside of a box, that way the clips will stay home.

Bill Heher · « **Reply #18 on:** February 24, 2010, 09:41:35 PM »

I only take 1 out and push the pin out that side, unless I'm replacing the piston. And I always push the pin back and forth against the e-clips to make sure they are seated.

And Alex- make sure you look at the crank pin closely- if it hogged out the rod end it may be galled / scratched. A new rod on a bad pin won't last very long, but Fox are pretty sturdy- just something to check while waiting for parts.

Marvin Denny · « **Reply #19 on:** February 26, 2010, 09:45:43 AM »

Yes you can pour it off through a filter and save it, however I just leave mine in the crock pot, put the lid on it and set the pot up on a high shelf in my garage so it won't get knocked over or pets get into it. I have used mine now for two years without draining it off nor filtering it and it still does a good job of cleaning. I have probably cleaned aroubd 150 engines with the Anti-freeze that is in there. I have twice had to add water as it does evaporate off somewhat.
If you do not intend to use the pot much, it might be better to go ahead and pour off the antifreeze and clean the pot. I caution you to NOT try to use the pot for food-stuffs now that you have used antifreeze in it. The poisonious stuff soaks into the pores of the crock and will come out when you put food into it to cook.
Bigiron

John Desrosiers · « **Reply #20 on:** February 27, 2010, 05:40:55 PM »

If you are using tires for electric powered planes the fuel that you are using will eat them and you will get black goo all over your plane.

Douglas Ames · « **Reply #21 on:** February 27, 2010, 10:45:56 PM »

Quote from: John Desrosiers on February 27, 2010, 05:40:55 PM

If you are using tires for electric powered planes the fuel that you are using will eat them and you will get black goo all over your plane.

My brain just locked up on this one

??