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Author Topic: Fox .35  (Read 1804 times)

Offline Mike_Fitzgerald

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Fox .35
« on: January 02, 2021, 03:17:46 PM »
Anyone on aboard that can impart some expert knowledge about fuels for Fox .35 engines...I know the recommended Fox  fuel is 5%-10% nitro with  29% castor...Would not a modern synthetic oil like Klotz KL-101 (80% synthetic & 20% castor) provide adequate lube as well?   

Thanks,   Mike
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Online Dan McEntee

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Re: Fox .35
« Reply #1 on: January 02, 2021, 04:10:04 PM »
Yes it would, and this has been hashed extensively. You just need to be in the same area of total percentages, 25% to 29% for lower time engines. Many have drifted away from all castor for quite a while, after discovering that even an even mix of oils tend to varnish the engines a lot less, and have even ventured into the 15% nitro range for certain situations.
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Online Dave_Trible

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Re: Fox .35
« Reply #2 on: January 02, 2021, 05:19:56 PM »
Well the Fox does like the castor to stay cool.  They never were fit very well and the materials are not real high grade.  They can get hot easily and will corrode if not kept well lubed.  The most important thing is that if your Fox is older and has been run much on castor fuels it builds a varnish inside.  If you then put synthetic fuels in it, it will 'clean' the engine, remove the varnish and basically destroy the piston/sleeve fit making the engine about useless.  If you start with a brand new engine then you could run SOME synthetic but I'd still have at least 50% castor to handle the friction heat.  Also the castor is fairly thick and may help seal sloppy fits just a little.  I just stick with the castor in mine and not worry about it.  Yes they get slimy.  That's part of why Fox's are sort a hobby of their own.

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Offline phil c

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Re: Fox .35
« Reply #3 on: January 03, 2021, 08:00:09 PM »
The main problem with the Fox 35 is the iron piston and the steel sleeve.  They can take a long time to break in and if, by mistake, they get off too lean and overheat they can be damaged and even completely shot in one flight or two.

Castor oil has the property that when it is overheated,(in a lean running engine), it polymerizes into varnish.  The motor will probably not run at all, and can't run properly until it is cleaned up.  The varnish can provide some protection against ruining the piston/sleeve.  Soaking in paint remover, or other solvents for degumming cars, should take off the varnish.

If you can put it back together and use just de-gummed castor in it  it may recover and run well again.

All the synthetic lubes are designed primarily for better metallurgy- in this case ABC or similar setups.  A small amount of castor mixed in will protect the ABC  from overheating damage, although it may require de-gumming the engine.

You can't ruin a stock Fox 35 by running it in a 4 cycle with 29% castor.

Also check the fit of the shaft.  I had one Fox 35 where the tight shaft would never let it run for more than a minute or so before it got hot and stopped.  Finally figured out what was going on and honed the bearing out with 2000 grit paper to get it to run.

Also be very careful to tighten the head bolts as evenly as possible when reassembling the engine.  It is very easy to get one or two screws too tight and bind up the motor, or the case or head is slightly mis-machined and can't be tightened properly.
phil Cartier

Offline ericrule

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Re: Fox .35
« Reply #4 on: January 13, 2021, 11:24:18 AM »
Great advice from Phil and Dave!

Over some 25 years I had Larry Foster modify over 1800 Fox .35 engines and subsequently sold them through RSM Distribution as L&J Fox .35 competition engines. Here is what we did to modify them so they would run with any of the top competition engines:
1) balanced the crank shaft
2) machined the bottom of the mounting lugs flat so the crank case would not twist
3) replaced the standard back plate with a "stuffer" back plate
4) replaced head and back plate bolts with socket heads (6- 4-40 x 3/8 and 3 - 4-40 x 1/4) and used a torque wrench to insure even torque
5) checked front bushing for proper fit
6) cut a groove inside the bushing and attached this circular groove to the existing oil spillway groove to provide a suction and stop fuel from blowing out the front end
7) polished the piston and inner liner surface for a perfect fit
8) drilled holes in the con rod ends to provide lubrication to the wrist pins
8) filled the bypass port to reduce the amount of raw fuel that could be thrown into the cylinder
9) replaced standard Fox head with a custom machined RSM Hemi Head
10) replaced Fox back plate and head gasket
11) replaced Fox needle valve and spray bar with ST.51 needle valve assembly.

In addition to these mods we always added a note with a strong recommendation that only fuel with a 10% nitro and a MINIMUM of 28% castor oil be used. The added nitro guaranteed that more fuel would run through the engine than would using 5%. The additional lubrication was essential to lower the temperature while running. Also the castor would paint a layer of varnish on the piston and liner to fill the inevitable scratches thus providing better compression.

Offline Dennis Toth

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Re: Fox .35
« Reply #5 on: January 13, 2021, 11:43:15 AM »
Mike,
Go to the Engine section of this forum and read the Care and Feeding article by Randy Smith, it has all you need to know about fuel for the Fox 35 and any other engine. The short answer on the use of Klotz is use it in a 50/50 blend with Castor and the total oil should be around 25% - 29%. I simply buy a quart of 5%N with 29% Castor from Brodak and a quart of 10N 23% Syn, mix together and get about 26% total oil, has worked great for over 10 years in my Foxes even with mufflers (just watch the prop load I run 9 1/2"x6).

Best,  DennisT

Offline RandySmith

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Re: Fox .35
« Reply #6 on: January 13, 2021, 01:50:20 PM »
Anyone on aboard that can impart some expert knowledge about fuels for Fox .35 engines...I know the recommended Fox  fuel is 5%-10% nitro with  29% castor...Would not a modern synthetic oil like Klotz KL-101 (80% synthetic & 20% castor) provide adequate lube as well?   

Thanks,   Mike
I have been asked many times to help explain why we have  so many things that can affect the run quality of Stunt engines. I will touch on a few of them , and hopefully help to eliminate some of these problems . Among them are tanks and fuel systems, glo plugs , fuel ,and overheating
  What are things that make for a  great, or  bad engine run. We see these things most every weekend, and it is  a very big point of frustration to many modelers. We all want our engines to run right, and it is  nice when it goes through the pattern smoothly, coming on and off, exactly when and where you want it.  Unfortunately, a lot of times, they growl , belch, shut off ,seem to have a mind of their own ,and are a total pain to deal with.  One of the biggest causes of this that I have seen is improper fuel.  Fuel is one of the most critical aspects in running model motors.  Use the right fuel and you will probably notice nothing; the wrong fuel will have you grumbling, or worse, will have your motor screaming, belching and running with absolutely no consistency whatsoever.

Most fuels on the market today use a synthetic base and are blended for the R/C sport flier.  These are typically very low on oil content, usually in the 12% through 15% range.  This is never acceptable for our use in C/L Stunt.  There are many reasons but the most important is the fact that we normally do not run our engines in a peaked two cycle, but rather a broad range of four cycle and rich two cycling.  Any time you run with the motor set to come on and off in the maneuvers (like a typical 4-2 break) you are not only asking the fuel to lubricate the motor, it also has to cool the engine.  The only way you can run in a 4-2 is to heat and cool the parts in the combustion chamber very rapidly.  This makes the oil content critical, because it’s the unburned oil that helps carry away the heat.

Years ago, most fuels had only one oil ,castor.  This is still a very good oil with many good but some bad points.  Some of its good points; it carries heat out of the motor and gives a good plating action on all surfaces, especially when they’re hot. It also has tendencies to move toward hot surfaces, helping to protect them.  A few of its bad points; it burns and sticks to the piston sides and the ring groove and all other parts that are hot enough, and will carbonize the chamber. It will stick rings in their grooves, freeze wrist pins and build up ridges on sleeves.  This causes excess friction and heat and will ruin your motor in time.

The alternative to castor is synthetic oil and almost all fuels have these in them; the vast majority has all synthetic.  Virtually all fuel manufactures use one type of synthetic; these are normally polyalkylene glycol based oils.  They are mostly made up of alcohol started linear polymers , of oxypropylene groups.  These are made by several companies and are available in a large range of molecular weights and viscosities.

This group of oils is the modern version of the old Ucon oils and also have good and bad points.  Some of the goods points; they are very good lubes without containing any wax; they have outstanding load carrying capacity, film strength, anti-wear properties, are resistant to sludge formation, and will help keep your engine clean.  The bad points are they give no rust protection by themselves, they don’t plate hot surfaces as well as castor and they burn at high heats.

As you can see, both oils have advantages and disadvantages to them; it’s for these reasons that they work much better blending together than they could ever work alone.  Throughout many years of flying ,testing and other research have proven this to me beyond any doubt; plus you can see this for yourself.  Recently, a friend of mine had a motor that would go into the pattern and lean out and act very inconsistently.  The only change that was made was to substitute one tank of my fuel in the model.  The results were drastically different; the motor now ran very smoothly, going into a two cycle instantly when the nose was raised and back into a four cycle instantly when the plane was leveled.  This was tried back and forth both fuels; his and mine.  The results were  the same every time. I see this type of thing happen much too often, and it is extremely frustrating for Flyers to deal with. They often blame these fuel problems on cooling, cowlings, motors ,fuel filters, and unfortunately some don’t have a clue how to recognize or  solve this problem. This is  a frustration that you can live  without!

I would like to tell you there is one Stunt fuel formula to run in all motors, I said I would like to tell you that…unfortunately this is not the case, and will never be as long as we have such a wide range of motors and running styles.  What I will tell you is a good formula for the most common types of engines.  Make sure you pick a fuel supplier who will give you consistent fuel day to day ,and will blend fuel for your motor needs or has fuel to match your needs.  Stay away from any supplier who will not tell you the oil percentage, or who say one type works for all motors. I see this  much to  often also, It is unfortunate, but a lot of fuel manufactures will try to fool you about the oil and nitro percentage. One trick is to measure  by weight and not volume. Doing so, they can claim that the fuel is  for example 18 % oil , when in reality it is only 14.9 % oil content. Using weight  for ingredient , they can put in a  lot less oil and nitro . Other things are changing oil types, going to cheaper Nitro’s, and adding in other types of Nitro parrafins.

   So what percentage do you try? For motors like Fox .35s, OS Max 35s or the old McCoy’s and K&B’s, use a fuel with 26 to 28% oil content; preferably half castor and half synthetic, up to 75% castor  is OK. These  motors have very small bearing surfaces, and are subject to much wear and heat, most are all plain bushing motors and most have unbushed rods. They need a lot of  oil  to help cool the engines. Since these motors run hot, they need  extra oil to keep them lubed,clean, and to carry out heat . If you have one of these that is  in very good  shape but, is  just starting to get some brown or black varnish plating on it, the synthetic mix will clean it  up for you, resulting in increased life.  Do not use the synthetic  blend in an old motor that has a lot of time on it with all castor fuels; the synthetic will remove the castor varnish off the piston and sleeve and will in some cases, leave you with the worn-out motor that had to start with.  Also always try to NOT use  prop shaft extensions with these engine, as it adds a  lot of  wear on the crankshaft bearing.

For motors with larger bushings and bushed rods like to OS FP , Magnum GP series, Tower, and  Brodak’s  a 22-25% half-and-half oil mixture works the best.  For S.T. .46 51,and .60s and most all ball bearings Stunt motors, a 23% half blend works best. Again the Synthetic blend will help keep the engine  clean, and insure long life. If you use  all castor in these  types, it can stick the ring in the groove , resulting in poor compression and  shortened engine life. If you have a ringed engine that castor has gummed up badly, most times running the synthetic blend will free the stuck ring, and the engine will  return compression and  power for you.
   The tuned pipe motors like a little more synthetic and I recommend a 15% synthetic, 7% castor blend or a  20% half and half with 1  ounce of Aero-1 fuel supplement. Although many use 1\2 – 1\2  with great success.  This works very well in the  Precision Aero , OPS and Max VF engines,  Super Tigre  Thunder Tiger, AERO TIGER and most all of these type engines..

Randy

Offline BillP

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Re: Fox .35
« Reply #7 on: January 14, 2021, 08:32:06 AM »
Great advice from Phil and Dave!

Over some 25 years I had Larry Foster modify over 1800 Fox .35 engines and subsequently sold them through RSM Distribution as L&J Fox .35 competition engines. Here is what we did to modify them so they would run with any of the top competition engines:
1) balanced the crank shaft
2) machined the bottom of the mounting lugs flat so the crank case would not twist
3) replaced the standard back plate with a "stuffer" back plate
4) replaced head and back plate bolts with socket heads (6- 4-40 x 3/8 and 3 - 4-40 x 1/4) and used a torque wrench to insure even torque
5) checked front bushing for proper fit
6) cut a groove inside the bushing and attached this circular groove to the existing oil spillway groove to provide a suction and stop fuel from blowing out the front end
7) polished the piston and inner liner surface for a perfect fit
8) drilled holes in the con rod ends to provide lubrication to the wrist pins
8) filled the bypass port to reduce the amount of raw fuel that could be thrown into the cylinder
9) replaced standard Fox head with a custom machined RSM Hemi Head
10) replaced Fox back plate and head gasket
11) replaced Fox needle valve and spray bar with ST.51 needle valve assembly.

In addition to these mods we always added a note with a strong recommendation that only fuel with a 10% nitro and a MINIMUM of 28% castor oil be used. The added nitro guaranteed that more fuel would run through the engine than would using 5%. The additional lubrication was essential to lower the temperature while running. Also the castor would paint a layer of varnish on the piston and liner to fill the inevitable scratches thus providing better compression.

Hey Eric, what did you plug the bypass with?
Bill P.

Online Al Ferraro

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Re: Fox .35
« Reply #8 on: January 19, 2021, 11:05:46 AM »
Hey Eric, what did you plug the bypass with?
I did a of running and tuning on a few Fox 35 Stunts over the past two years using a Ringmaster and a Nobler. I did not like the way the engine ran with the popsicle stick in the bypass. The engine would not settle down in a 4 stroke and ran more in a 2 stroke, and yes there was no burp on the Ringmaster. I found using a larger .156 spray bar like a ST or PA needle valve assembly was to answer to get a nice 424 break with no burp with the Ringmaster profile.  With the .156 spray bar the engine answered the needle a whole lot better on the ground too. I feel the size of the venturi and Fox 35 stunt needle valve assembly together leaves to large of a choke area for a slow running engine like the Fox and not mixing up the fuel well. Using the engine set up with the larger spay bar I did not notice any loss of power in flying the stunt pattern with either plane. Using a very small spray bar in my Fox 35 Stunt Speed engine does make more power for a faster top speed (117 mph in the air), but that engine is running at over 16000 RPM.
Al

Offline Dennis Toth

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Re: Fox .35
« Reply #9 on: January 19, 2021, 07:51:19 PM »
Al,
One thing to try in your Fox is to set the spraybar hole just below 90 deg across the venturi. I use one of Randy Smith's PAfox NVA with the hole pointing to the rear wall. Also, don't over prop it if you run a muffler. I have run mine on a 9 1/2" x 6 prop cut down from an old spoon blade wood Top Flite 10x6.

Best,     DennisT

Online Al Ferraro

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Re: Fox .35
« Reply #10 on: January 21, 2021, 10:43:00 AM »
Al,
One thing to try in your Fox is to set the spraybar hole just below 90 deg across the venturi. I use one of Randy Smith's PAfox NVA with the hole pointing to the rear wall. Also, don't over prop it if you run a muffler. I have run mine on a 9 1/2" x 6 prop cut down from an old spoon blade wood Top Flite 10x6.

Best,     DennisT
  Hi Dennis,
          That is how I install my spray bar. The prop that is working great for me is the Bolly Clubman 10.5x5. Instead of a muffler I use a Macs header pipe to keep the exhaust oil off the plane.
Here New Years day 2021 in 36 degree weather running my Fox.


Al


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