hsukaria

Yep, mine is the 55AX. But before any big stink starts about the OS peeling liners, this one was my fault. I didn't notice that the filter/clunk in the fuel jug fell off and I was almost out of fuel in the jug. I filled the tank and flew up ok, and then some dirt clogged the carb real bad during flight and the engine leaned out and quit. I subsequently cleaned the carb, but the engine would never run longer than a minute, when the engine would heat up and lose compression. The liner shows where it peeled visibly. I guess a ringed engine might have been a little more robust?

I have been wondering if the ASP 52 or JBA 56 p/l sets might work.

1QwkSport2.5r

Franken Fox update; Project FDX. MDS .40 Piston/Liner/Head, Fox .50 case, crank, rod, Fox EZ carb (.330") -- 10x6 APC 10% nitro 20% castor MC59 glow plug - 11,500rpm. 25% nitro 20% castor gave12,300rpm. That's with .035" head spacing. Making some modifications and will retest. Idle speed was stable at 2,400rpm. Carb is probably a bit too big at .330", had the airbleed closed to get a good transition from it and even then it was a tad lean. Top end was okay though the big head spacing is limiting power.

hsukaria

Are all the large frame Fox carbs the same venturi size? (MkX, EZ, and the new TN?)

1QwkSport2.5r

I don't believe so. I think there are 4 sizes of MkX carbs, and at least 2 sizes of the butterfly carbs. I'm not sure about the EZ carb - I think that one only came on the .46 ABC from the factory. I could be wrong. I have a large case MkX and the EZ but both are .330" chokes. I have a set of MkX's for the Twin, but I don't want to use those as they're set up for another guy's twin. I should try the butterfly carbs as a way to get them sorted out maybe.

hsukaria

My 74 came with an EZ carb, but I bought it used. I then bought the new TN carb and I believe it has it is the same size as the EZ. When I swapped carbs temporarily and put the TN on the 45, the throttle response and idle remained very good, but the mixture adjustment became very sensitive on the smaller engine.

hsukaria

I removed the cylinder head on my Fox 45 and measured the bore size with my new handy-dandy caliper (it's digital!!). I measure approximately 0.847 inch. Does that sound right? What is the stroke length for the 45? I think the piston ring will need replacement due to lower compression and performance. While I'm at it, I will replace the bearings. But I will get 'round to it' someday.

1QwkSport2.5r

I will bet it has a .790 stroke. Approximately .445ci so yeah .847 sounds right.

Hobbsy

My Feedback: (102)

.60's and .74's came with the same EZJust as the .46.

1QwkSport2.5r

That's a huge carb (.330") for a .46! Makes sense now why they said the EZ carb was so lean in the midrange on the .46.

The FrankenFox doesn't like a lean midrange. We closed the airbleed off and it's still lean in the midrange. Have to throttle her slowly or she'll deadstick. The FrankenFox went from a .50 to a .425 which probably seems worse. The .50 throttled okay on the EZ carb on diesel.

hsukaria

Hi folks, I have decided to go ahead and replace the piston ring and bearings for my Fox 45. Is there a trick to removing the prop hub? It seems that every engine I rebuild has a different setup, and the Fox 45 is no exception, It looks like it is made out of a stamped sheet metal. That's a new one to me.

1QwkSport2.5r

Doesn't look like a factory prop driver to me even as crude as some Fox stuff is. Should be a tapered collet anyhow. Warm it up and give it a whack with a piece of wood.

earlwb

Yes the prop driver is metal and it has a brass tapered collet on the inside. In order to prevent damaging it, you can heat up the engine and prop driver and press out the crankshaft with a arbor press. As soon as the crank moves back a little bit the prop driver will come loose. Sometimes it comes loose after you heat it up good with some gentle taps too. heating up the engine crankcase to around 250 degrees causes the crankcase to expand and loosen the bearings. of course you take apart the engine to get the cylinder, rod and piston out of the way.

I had forgotten it, but you can freeze the engine good. Then using a torch, set for a small flame, and heat up the drive washer only and it will come off without much if any effort.

Cougar429

My Feedback: (3)

if you are doing any hitting on the end of the crank, at least use a center punch on the prop thread end or a piece of wood or soft alloy to reinstall the crank back into the case and bearings. In either case, many very light taps are preferred to a few mighty whacks. Don't forget, any force applied has to travel through the bearings.

In regards to that prop hub, the tapered sleeve is compressed down when the prop is tightened and likely friction will keep it that way until "persuaded" to let go. with no belt groove a puller has nothing to grip without damage and the wall thickness is pretty low back where it overlaps the case nose. In addition, old fuel/oil and other contaminants can help glue everything together.

I find with a good soak in hot glycol the hubs have a tendency to come loose anyway.

hsukaria

Thanks for the help again. I might decide to leave the bearings unchanged after all since they are not in very bad shape. But I will replace the piston ring for sure since the compression is weak.

Cougar429

My Feedback: (3)

If still together and no obvious damage visible through the exhaust port, do the "Bubble Test" with soapy water to confirm you aren't leaking around the head/button area. Easy check before teardown.

If the motor has been sitting for a long time, at least pull the back cover and flush any crud out of the case with alcohol. Don't need that rolling around the bearings and it will give you a chance to have a boo at the rear bearing.

earlwb

If i remember correctly, I have to look it up, the Fox Butterfly carbs came in two or three venturi bore sizes for the 40's (45's) and the .60s, the old .78 might have had a different bore too. The MK-X carbs had four different bores and a Fifth Q500 carb that was bored out even more. The EZ carb had two bore sizes, one for the 45's and one for the 60's and 74 engines. With the latest TN carbs, I assume they had two different bore sizes for the .45's and the .60/.74 engines.

Ok looking at my notes.
The .40 and .45 engines had a carb with a .290 to .312 bore depending on the production run down over the years

The Fox Eagle II, III and IV .60and .74 engines had a MK-X carb with a .330 bore. The Fox Hawk .60 and Eagle I .60 when sent in for servicing had the MK-X B carb put on with a bore of .312 size.

There was a MK-X F carb with a .350 bore for tuned pipes too.

I think that the EZ carb had a .312 bore for the .45 engines and a .330 bore for the .60 and .74 engines.

The Quickie 500 .40 engines had carbs with bores of .350, .360 and even .375 depending on the production run at the time. One could put the MK-X A type carb with a bore of .290 and it became a Sport Quickie if I remember right. it would then idle fairly well.

hsukaria

good to know. I will go measure the venturi on my EZ, TN, and later when it arrives, the MKx carb. The EZ and TN are from the Eagle 74 and the MKx is from the 45.

1QwkSport2.5r

My .46 ABC came with a .330" EZ from the factory. The .50 I had acquired had a .330" MkX on it though I'm unsure if that's a factory item or not.

hsukaria

Cougar429, I took my time to check for air leaks with soapy water because I thought that was a far fetched possibility. Well, I did check with soapy water tonight and this engine (45) leaks terribly. I have never seen anything like it. I was told the head button is the higher compression/low nitro version and you feel a little compression if flipping the prop hard, but going a little slower just loses all compression. I was getting giant soap bubbles from under the head. I also had just replaced the Miracle glowplug with some unknown plug and the seal in the plug also leaks!!!!!!!!! I can replace the plug, but what do I do about the head? Granted, I could possibly torque it down more if I replaced the worn out phillips screws with allen screws. But still, is there anything else that has to be done?

Sport_Pilot

Yes replace the head screws and torque it down in a star pattern. If it still leaks then try putting some rubbing compound on the top of the cylinder, put the head on top and work back and forth to polish the surfaces.

Cougar429

My Feedback: (3)

If performing that one, I would definitely want to protect the other components from contamination. Best way would be to pull the sleeve, but dropping the piston and stuffing a wad of putty over top to cover the ports may help. Personally I would invert the engine during the process as it does not take much spinning to work the surfaces.

NOTE: You would want to avoid getting any between the button and inside of the sleeve bore. Those should remain as tight as possible.

It would be a good idea to flush out everything, even the bolt holes, after the end. The abrasives can do serious damage if they get inside.

I would agree the first and easiest fix would be to replace those head screws with allan head cap bolts. I find not only are they of a harder material, but by design can give me a much more consistent torque than using a screw driver.

One other option would be a gasket between the button and sleeve. That one may not be as easy as there are almost infinite sizes around and I never seem to find the one I need.

ps. If you do not have easy access to rubbing compound, (there are different grades of that and lapping compound) you can at least try toothpaste. Some have a mild abrasive.

Sport_Pilot

That is unnecessary as rubbing compound does no damage to those parts that is not rubbed. That is contact does no damage but physical rubbing may. Just wash the remaining rubbing compound off with soap and water.

Tooth paste works great on yellowed canopies, and headlights.

Cougar429

My Feedback: (3)

Sport Pilot, I personally would not want to run an engine with the abrasive remains of rubbing or lapping compound within the case or cylinder area. Care can minimize any that migrates away from where you are working and a good cleaning should be mandatory, but I was trying to indicate problems that can occur if you aren't as diligent.

Sport_Pilot

If you are careful the rubbing compound will only be on the head and the tip of the cylinder. All you really need to do is wipe it off. Duke Fox used to lap a tight piston and sleeve with lapping compound and even Comet abrasive cleaner have been used for the same thing. Rubbing compound is not nearly as abrasive as lapping compound.

Charley

My Feedback: (2)

Am I the only one who remembers that Duke sold some lapping compound called something-lux (can't remember the something ) for hastening the break-in of the lapped-piston engines?

CR