All I can think of (and I'm not a huge expert) is that it's down on compression ratio -- not compression seal.  Particularly if you got it used, take the head off and see if it has multiple head gaskets stacked up in there.  If there are -- take some out, and try again.  Someone may have been confused, or flying with tons-o-nitro, or both.  While the head's off, make sure that the liner is in correctly, both seated correctly on the case, and oriented correctly (as the piston goes down it should uncover the exhaust port first, then the transfer port).  Piston, too -- the baffle should be away from the exhaust side (I think).

I assume you're using a hot glow plug -- using a cold plug shouldn't cause that severe a problem, though.

That's it, I know no more, unless it's a primary compression (crankcase) leak.

     Hi Again:

     After a good night's sleep, I got the idea of flushing this engine with carb cleaner and rinsing with fuel.  I will attempt to run it again today.

     Allow me to repeat what I have checked:

     Compression is VERY strong.

     It  will hold compression for a very long time.

     No base compression leaks.
 
     Cylinder is installed correctly.

     Tried different props, plugs, nva and fuels.

     The engine will run very rich and will scream in a 2 cycle as long as the plug is connected to the battery. It quits as soon as the battery is disconnected.  This leads me to believe that all of the plugs that I tried, were faulty.  However, they all ran well in other engines??

     Will keep you posted after today's test runs.

                                                           Stay well my friend,

                                                           Frank McCune

     

     

"Engine will not run with battery disconnected??"

That's the usual sign that the glowplug is not nearly hot enough. There are some very good (and suitable) glowplugs available. None made by Fox, IMHO. Thunderbolt R/C long reach (with idle bar) and Thunderbolt 4-Cycle (discontinued) are all I stock. So, what brands and heat ranges are you using?

Another possible potential problem is that you're using a short reach plug in an engine designed for long reach plugs. I'd pull the head and check to be sure the glowplug is at least flush with the chamber surface, if not a little "proud". I've seen that in a Fox .35 Stunt...very touchy on NV, didn't want to run rich, didn't want to run lean, and the clicker type NV didn't have a suitable detent. A Thunderbolt long/idle bar fixed it.    Steve

have u seen this engine run .i would pull a head shim ,or just pull head and see how many shims it had

one year we brought a nelson 15 good year to Munciie that ran great here at sea level in FL. .in Muncie it would not run with the bATT DISCONNECTED EVEN AFTER A LENGHTYworm up , we pulled a shim and it ran great taking 3rd

     Hi Steve et al:

     No, I do not have anything other than 10% nitro fuel at the time. I do have the fixins to brew whatever blend I wish.

     I pulled the engine down and saw that there was only one aluminum head gasket installed. I ran the engine through my ultrasonic cleaner and reassembled it.  Of course, I now have a poor piston and cylinder fit that I hope will improve after I break in the engine again! I can never reassemble an engine that had a great p&C fit to quality of the original fit! Perhaps there is just not enough metal left to establish a new seal. It may also be that toe p&c are not concentric and will never fit the same way again tto form a good seal.  Perhaps varnish will seal up the new p&c to form a good seal. Lol  A friend of mine suggested to place a 10x6 prop on the engine and feed it a pint of 35% nitro with about 30% castor oil to form a new varnish seal.  Run it hot but not over lean on the test stand.

      I will run it for awhile today to see what happens.

      Of course I had to play musical screw to get the head/crankcase seal to stop leaking.  I think that those old Fox heads always needed to faced to true them before attempting to reassemble the engine.  Three thousands of an inch or more was often required to get them straight. 

      I wanted to use this engine in an OTS plane as it had such a great p&c seal.  Talk about easy starting!  It is an older Fox with the filleted piston baffle and the brass end pads on the wrist pin. Any idea as to when it was made?
                                                               Stay well my friends,

                                                               Frank McCune
p.s.
     The prices that are on the Fireball Plugs reads 39 cents.  I must have bought them in the 70's! Lol

I'm thinking you should run the Fox 35?

Hi Frank,

The only thing I can tell you is that the Fireball "Yellow" and K&B "Std" are NOT "HOT" plugs.  I know there can be an exception to every rule, but every 4-2 engine I have used had to have a HOT plug to run "correctly".

I would put more bench time on the engine.  Also at least 25% oil and mostly castor (as I am sure you know).  During bench time I would run 25% castor, 3% synthetic to get 28% oil and still keep it fairly clean inside.  Plus all that oil does have a cooling effect on the engine (as you also know) so a non broken in engine running a lot of oil at a constant air speed (0 mph forward) should really need a hot plug just to keep the fire lit if the temps are like they are here!

Also, bench run it with a 9-3 prop, or a prop 1" less diameter and 3"-4"pitch. George and Big Art recommended this.  I got a 10-3 1/2 Top Flite to break in the .35 and .40 engines I have on Big's recommendation.

BIG Bear
RNMM/AMM

Frank, a couple of other things that could cause your problem. When using the electric starter I am sure you wiped a little aluminum off of the back plate. That will go right to the plug and destroy it in short order. The other thing, when you had it apart was the rod loose on the wristpin or frozen to it. They can get stuck on there from congealed oil and put the rod in a bind or push the wristpin into the cyl. wall. Just a couple of things to check other than getting a good hot plug in it. I hope you find your problem as I just went through one of these and it runs great on the test stand. Hoping to fly it soon in my Sterling profile Mustang.