Hello
Something is wrong with your tacho, fuel (stale includes water?) or plug or both engines are damaged/assembled wrong.
 Even a well worn engine with good fuel and a good glow plug would give more rpm .
Regards Gerald

       Hi All:

        I tested my two OS SF .46 engines today to determine if they would pull a Score.  I was greatly disappointed in the power output from both engines.  One engine is ABC and the other is ringed.  They both appear to be at least 3000 rpm slower than other .46 engines.  The ringed eingie is like new with a new ring installed and is broken innfor ue.  The ABC engine is very tight at the top of the stroke where starting is very difficult.  Neither me or my Sullivan starter has the power to turn this engine over without first warming the cylinder.

     Here are a few results from my tests today.  The tach was checked for 3600 Hz prior to testing.  Both engines have a venturi size of .285 and a ST style of nva.

     Ringed engine 10-6 prop 11,160
               
                           11-6 prop 9,300

                           12-4 prop  7,900

     ABC engine      10-6 prop  10,130
 
                            11-6 prop  8,590

                            12-4 prop  8,900

       I thought that these engines should turn a 10-6 prop in the 13000-14000 rpm range.  They run very smoothly and appear to be good engines but they have a bit left to be desired if I want them to pull a Score!

        The fuel used in the test was 11 castor, 11 syn. , 10 nitro, and same plug.

         Thoughts/suggestions?

                                                                                                                                                            Tia,

                                                                                                                                                             Frank McCune

 

Hi Frank

All of your numbers  are  low,  BUT  7900  RPMS with a  12 x 4 on the  46 ringed engine,  You have some type of BAD problem  somewhere   , or  your  Venturis are much smaller than you listed,  Tach problems   Something there is  wrong
try another  tach  re measure the venturi  size

Randy

9 mm/.354 would definitely increase the power on the bench, but it is VASTLY too large to actually use in flight.

   Something else is going on, because the RPMs listed would be blubbering rich with it otherwise working, and a .281 venturi. You should able to swing a typical 12-4 at 12,000 RPM peaked out, at least, with this system, and I have seen that done easily - in 105 degree weather! The numbers you are getting could easily be managed by an average ST46.

   This seems to happen time and again - there is some really obvious factor that we are missing somewhere, something really fundamental, a systematic misunderstanding.

     Brett

"The fuel used in the test was 11 castor, 11 syn. , 10 nitro, and same plug."
Is this a NEW plug???
Had a similar problem with another motor that ran THE SAME every flight, until a contest at another location with similar altitude, temp & humidity. New plug solved the problem!
Good luck & "Tight Lines!"
Wes

When you look in the exhaust port are all the ports lined up? Did it drop a wrist pin clip and score the cylinder? Seems funny they are both down on power, must be something in common.

  More disturbing/confounding is that this is the latest in a series of different engines, all of which apparently have some severe defect or almost inconceivably low performance. There is some, probably really basic, element that we are missing here. The best suggest was above, maybe the tach isn't working, it should be possible to tell the difference between 12,000 and 8000 without a tach.
 
   The stock 46SF muffler *is* restrictive, but, not *that* restrictive. 8000 rpm with a 12-4? A Fox 35 might manage that, expect a 46SF to be in the ballpark with an ST60 with this size prop.

    Brett

p.s. This is beginning to sound kind of familiar, actually  - I saw a very similar situation with a 46LA about 10-12 years ago at the NWR, that is, less power than a Fox 35. What is the provenance of this engine - has it been "improved" or "reworked for stunt"?  Or did it come straight out of the package from the OS factory? 

   This is a growing issue - engines that have been "improved" and then the source and the type of modifications lost. The unsuccessful modifications tend to get passed around many times, during which, any notion about what was done or what the history of them was lost. The Randy modification to the 46SF is about a match for an ST60 in all regards, but *many* of the others are late-70's style "drop the liner" deals where all the power just goes away.

   Another possibility is a stock engine with the liner in backwards. In that case, it will get *stinking hot* while also putting out clouds of smoke and no power. It's unlikely that they are all backwards, unless they have been "improved", in which case almost anything is possible.

      I am beginning to think that these two engines are choked down too much for maximum power.  I noticed that a rc version of the .46 engine had a carb bore of .308"!!!!!  Should this mean anything to me?

   No. While you might be able to get more power with a larger venturi (while severely impacting the run quality), it should be several thousand RPM more with the venturi you have. ".281", that is, probably whatever it comes out when you drill it with a 9/32 drill (which is likely around .283 or so, depending on the quality of the grind), is a very common size to use. I have sent people off with a 12-4 Eather or 12-4.5 Bolly, set the needle to 11,200, and they are good to go, numerous times.

   This stuff is not magic, it's not "well, whatever works for you", and the 46SF is hardly a new, unknown quantity - it's been around forever. engines are generally simple and straightforward to understand, at least as far as this sort of thing goes. The difference between the power at 8000 and the power at 12000 is more than a factor of 3 - you are getting maybe 30% of the power that would be otherwise expected. There is something very fundamentally wrong here, it's not a slightly tweak away.

    We are probing to try to figure it out, not to annoy you, because you seems to have these sorts of issues time after time. Your air is not consequentially different from ours, at least not by a factor of more than 3.

   Randy has built up and run these forever, I have assisted in at least a dozen 46SF runners at the field, with generally good results. We (usually Ted Fancher and I)  do have a few typical changes we suggest, but they are minor tweaks to move the needle around,  none that take it from 8000 to 12000. It's not really an experiment at this point, something else is going on.

    Brett

   p.s.. again, where did these engines come from? Used, from someone else? Or straight from the box, unused and in the factory condition? Because the most obvious cause is "modifications", and improper modifications have definitely caused the same issues before, in fact, the vast majority of modifications cause abnormally low power, because they are misguided.  If you don't want to say in public, PM me.

       Hello Brett et. al.:

        A big thank you to all of you who replied to my post!

       I bought both of these engines from fellow club members. The ringed engine looked like it was new but after inspection, it was determined that the ring was broken.  I replaced the ring and all appeared well.  The ABC engine looked as if it had been run with many gallons of castor fuel as the sleeve and top of the piston were both very black with burned castor.  However, this engine still has a bit of pinch at TDC and the compression is so strong that it is very difficult to flip over for starting.  I am too weak to finger start it or use a chicken stick to turn it over.  It laughs at my Sullivan Starter! Lol  I can only start it by whacking it very smartly with a large club! It appears the  compression is sky high.  It is very difficult to turn over via the propeller!  Once the plug has been removed, it is a joy to turn over with no surprises.

       One thing that I noticed about the ABC engine is that the inside of the head is CLEAN and has a 40 cast into the bottom.  I seems to fit the liner perfectly??? Why is the head devoid of any trace of being run and the rest of the combustion chamber is coated with a black residue? Perhaps a replacement head for some reason has been installed on this engine.

      Is the ST G .49 Sport figures in line with this engine running a venturi of .250"?  What size of venturi would work well with this engine and a ST nva.?

      The ST Sport is a great engine.  I think that it has a lapped steel/cast iron p&c and one ball bearing in the rear.  One flip starts and runs like a fine Swiss watch!     

      There is no evidence of any rework being done to either engine.  All is clean inside.

      Hey Brett, I think that I have noticed a pattern here with my engine problems.  I do not run any engines that I purchased new!  Perhaps this would end most of my engine problems. Lol Being a "Gear Head", I never met an engine that I did not want to give a good home. Lol Even ugly engines need love. Lol

                                                                                                                                   Thanks again,

                                                                                                                                   Frank

In case anyone thinks this is an aberration, a 1965 Fox 35 only ever modified to install socket-head screws (damaged in antiquity by my father, replaced in the last few years). He may have run ~5-10 gallons of Fox Superfuel through it, I ran at least *40 gallons* of X-Cel Hobbies 5% (mixed by Lew McFarland) through it, and it has only, at most, been brushed off with solvent and a toothbrush, no real cleaning. I guarantee my dad never cleaned it, or anything else, to any great degree, he almost aspired to be a hillbilly (despite being an exceptional engineer and effectively a VP at Westinghouse). This engine was getting tired (in *1979*) and I switched to a 1973 version to get a bit more power, but the engine pictured would still perform perfectly well. The biggest issue is that it has no practical way to attach a muffler, which was a non-issue at the time, but would probably drive me to use a later model.

 Exhaust port and side:



Top of head:



  If the engines you get are getting dirty or baked, you can probably assume that that something bad has gone on.

   Brett

    Hello Matt:

     I had the idea of running the ringed engine with the original carb installed.  This may give an indication as to what the problem may be.  For some perverse reason, I am leaning towards suspecting the air/fuel system as being faulty.  What else has been modified in both of these engines? The answer is nothing.  However, one must resist the inclination to only focus on one solution. 

                                                                                            Do not be bound by reality!


                                                                                             Frank
  I

we have the tecnology we can rebuild him . ! 

       One thing that I noticed about the ABC engine is that the inside of the head is CLEAN and has a 40 cast into the bottom.  I seems to fit the liner perfectly???

   Not to flog a dead horse, Frank, but just for future reference, the portion of the head that goes into the liner should be a very close slip fit, ideally to the point that it's hard to push into the liner if it gets cocked even slightly sideways - nearly the same as the piston fit. Under .001" clearance. Production engines don't have this, but the semi-custom engines like the RO-Jett and PA, the head/head button is fitted to each particular liner, and they are sometimes very difficult to get started straight enough to go in. I just tried to measure it, and while I can measure to a few ten-thousandths of an inch, a defunct RO-Jet 61 liner and head measure the same to the tenth. With both parts at the same temperature, I would guess its about .0002-3 interference fit, that is, a very light press fit.

    I don't know the exact dimensions, but making some guesses, making a 46 out of a 40 by just increasing the bore will probably result in more than .020" difference in the diameter of the cylinder - which is so much that is this alone could probably cause your lost performance. The extra space reduces the combustion pressure but is otherwise useless for burning fuel, it's much worse than just grinding out the combustion chamber or adding head gaskets, since more-or-less no fuel/air mix ever gets there, it's just dead space.

    What is very likely is that someone had some engine parts lying around, the holes lined up, so they just put the parts together to make nominally complete engines, to sell them - a Frankenmotor.  Don't blame the guy you bought it from, he may have gotten them that way, too. But I *have* seen people do things like put "40" heads on "46" engines on purpose, to "reduce the compression" which has inexplicably become Step 1 in the 12-step plan to "make it a real stunt motor", i.e. screw up an otherwise perfectly good engine and make them run like crap. Mission Accomplished! 

That's why they tend to get passed around from person-to-person-to-person, it doesn't work, they sell it, it still doesn't work, the next guy sells it, etc. There's a Fox 45 "Compact" around here that I have seen 4-5 different times, different people have it every time, it still has the same issues, and has gotten sold multiple times. I haven't seen it in about 10 years, maybe someone finally put it out of its misery.

    I am sure Randy has all the parts and compete engines, if you want one. As noted, it would be possible to machine a new head, or to sleeve the existing head, to make it fit. But, given that one of them is worn out, the other also needs a new liner, and there are many other, better, stunt engines widely available, you have to question whether fixing it makes sense.

     Brett

  Summarizing -  "modified" (by swapping parts, including the wrong parts, and by grinding), clearly disassembled and reassembled multiple times, and worn out.

    Since I don't actually know, is the bore the same between the 46 and the 40, or is it different (meaning the 40 head would be a rattle-fit in the 46, and exhibit abnormally low compression ratio)?  If so, don't dismiss the possibility that this was an intentional modification attempting to lower the compression *on purpose*, because I have seen people do that. Although more likely is that these were Frankenmotors assembled from whatever parts were on hand, to make them nominally "complete".


    Brett

Brett  the  46 has a  larger  bore, so  YES  it would be  a  rattle fit, this would cut power a lot

Randy

I take such tolerances from F3D engines, and Randy’s PA’s seem to have similar background. For cylinder/head fit 0,005mm (about 0.0002”) ř clearance is good. as you said, it has to be straight to get it in.
In running temperature the play goes to zero or a micron or 2 negative. L

Randy, do you have a piston/sleeve for the SF 46, does the VF 46 or the AX 46 liner fit? 

Frank,
If you're not going to use them I could just put them back together in the best configuration. The ABN would run better and the ring would run worse or be a parts engine. Then later if you find a piston/sleeve for the ABN you could just install it yourself knowing everything else is correct. 


Motorman

I will look to see  what I have, I have bearings and other parts  for the  SF, they are not  the same as the  OS VFs
I made  AAC  setups for both 40 and  46  in small quantities  BUT  I think those are all gone

Randy

Put the engines back together and ran them both with the good head. Used a Randy TT 11-4.5 which I believe is the right prop for these. 10% fuel and peaked the needle for all I could get.

ABC With muffler 10,300  No muffler 12,300

Ringed  No muffler 12,300

  Both of those are on the very weak side of normal, which is about what you would expect given their state of repair. 10300 w/muffler is off about 1500 rpm, which, given the circumstances, is about right. A new engine will pretty easily spin that prop 12000+.

     That's not a particularly good prop for it, I think the last time I assisted, the guy ended up running something like a 12.5-3.75 Eather 2-blade. The little 11.5-4 is OK for the LA, but a properly-working SF is much more powerful. The closest commonly-available prop is the APC 12.25-3.75, which was requested to be made by David Fitzgerald for a piped 46VF.

  Note also that the muffler is restrictive, as previously noted, but you might ask yourself what you are going to do with a 46SF that turns a 11.5-4 at 14,000+ RPM, at least on a stunt plane (which is what you would get with less or no restriction and an otherwise correct engine). Turning the needle will not fix that problem, at least not once it leaves the ground.

     Our solution - arrived at at the El Cerrito Flying Dons "Eat Chili and Fly Day" in about 1996 - was to ream out the hole in the muffler to about .312 (5/16) with a Fox prop reamer,  which is about as big as you can get it without removing the stinger entirely. "Our" being Ted Fancher and myself, on Bill Howe's 46SF. That was more than adequate to fly a 720 square inch airplane.

   That's why its rear-exhaust stablemate (40VF) uses a tuned pipe.

    Brett

Sorry to resurect our little NIGHTMARE , 

Looks like a LA 46 Piston & liner ( and rod ? ) might interchange with a SF 46 .
Obviously the LA has no boost ( third ) port . So this brings up a few questions .
If a LA is so marvelous , can a SF sans boost emulate its useability .

( my clone is a powerhouse , but that may be the fuel , the rate it burns it, anyway .  )

The  OS LA  46  P/S  is  not  a  match for the  SF 46

Randy

point the tach at an incandescent light.  It should read 3600rpm   60cycles/second x 60 seconds in a minute