Not much, as long as the heights are appropriate. Too low and any time you pull positive gees (i.e. every time you pull back on the stick) you'll drive the mixture lean. I imagine you dealt with that at installation time though.

If the issue is not cooling air flow, as suggested, reduce nitro. Just try it, you really should eliminate that variable to reduce guessing. Maybe you can borrow a tank or two? Preignition can occur if you use the higher end of the allowable nitro range, and you use a hot plug and if weather conditions are not helping.

As to running full throttle all the time - that should not matter one iota. It has to work there or you need to fix something.

MJD

Why don't you test first some of the easiest suggestions first?

fly the plane without cowl....low nitro fuel> that it does work ok in the other engines doesn't mean that it is good for all the engines, many engines are designed a little bit different even though they share the same parts and principles...the have different ports, some are ringed, some are abc, some have higher compression than the others, they behave different to nitro content or nothing at all.

Many of you are taking too much attention to the cowl stuff, and your cowling is not bad at all, but IMHO the problem comes from inside. Overheating and lean runs are related most of the time, and I've seen that the engine stops first due to the high temperatures rather than blow the plug first.... if the plug burns out it is due to wrong heat range, wrong fuel, and less likely from the quality of the plug, most plugs are virtually the same, differing in heat range, the size of the coil (longer on 4 strokes for example), but most of them use the same materials....

Lean runs and higher nitro than needed may cause extremely high temperatures.

Super tigre, like most of the euro eingnes, run well on low to no nitro. You can try buying a methanol quart and some castor from drugstore, it won't cost you much, and would be an easy test...

Check that the muffler nipple is tight.

I hope you get it to work properly...

best regards/saludos

Jorge

Okay, so here's the intial plan:
1) get a thermocouple on the head
2) run the engine on the ground, with cowl, using 10%, read the temp
3) Switch to 5%, repeat an compare temperaures.

4) Modify the cowl with better ducting
5) run the engine on the ground, with improved cowl, using 10%, read the temp
6) Switch to 5%, repeat an compare temperaures.

So, whats good temperature and whats a bad temperature?

I'll probably switch to a uniflow on pricipals but for these tests that should not affect the results.

This engine is made for 15% nitro so lowering the nitro won't make much differance and since it is made for higher nitro would actually run a bit hotter (I doubt it would be enough to notice) not cooler. The only time reducing nitro will make it run cooler is when it is detonating. But then a cooler plug would have the same effect. The issue is either air cooling, which I doubt is the problem because of the huge opening below the engine and head fins in the breeze. Or running lean, most likely after it has run a while and mostly when climbing.

Also I wanted to add:
What everyone has said is quite valid!
Super Tigers like lower nito fuels, I have one that I run 0 nitro and it runs quite well.
Problem is with the lower nitro fuels you get a lot less power, and it seems that prop you are running and the fact that you are flying 3 d would suggest that you need a lot of power to hold the plane up. Most of the guys in my club flying 3 d are using four strokes or gassers. Myself I do not fly much 3 d and tend to fly faster airplanes. Always overpowered, but very light weight, and low wing loading pattern and pylon type of stuff with some hotliners and alike thrown in. In your case you are pushing the envelope in a different way and with a low pitch high diameter prop you are spinning you engine up to it's max limit a lot, somethings gonnna give. Not being critical because I have burned out and blow apart more engines, and motors than I care to admit. The guys also have pointed out that cooking the plugs can be either to hot of a plug or to hot of a fuel, both of these can be issues. Cooking the rings tells me that you also have an issue of the cylinder being to hot, and not sinking the heat away from the rings as well as it should. Now we throw into the mix that you living in Texas where it get hotter than I care to have to endure, perhaps that is why I am obsessed with the cooling thing...lol

I sympathize with your problem, just keep in my that with so many variables it is hard to say from a distance exactly what is wrong. But you at least have some suggestions of things to try now that you may not have thought of. Now you have to try some things and see what the results are. I would also suggest you get a remote sensing temperature gauge, it will tell you a lot about you running setup as far as temp and alike they are cheap and everyone should have one in their flight box. Keep in mind you may have to run a bit richer than normal as you typically are flying at high throttle settings and the oil in the mix is not just for lube but cooling as well. It could be that your plane/engine/prop combo need to be addressed, due to the type and style of flying you are doing. Warbirds and a lot of scale airplanes (inhale sharply) at 3 d, deltas don't fly pylon that well, and high wings don't do pattern that well. I did not notice what you said you were flying you may well have mentioned the plane and I missed it, and that may not be an issue at all.

Just keep in mind you are pushing hard and to get the max out of the engine you may have to make some adjustment to keep it from breaking as often.
"She can't take much more of this Captin" Scotty...

The heli guys are say 200 deg F is a good running temp for 2 strokes, and I have used that as my reference.

It may well say in the manual, but who reads those...lol

good temperature is where the engine works good.... you change the fuel, plug, propeller, and you have a different temperature, the day is cold, or hot, and you have another temperature, so it is pointless, just like a factory needle setting (only good as a start point!!). You will notice that the engine is overheated because it cannot hold RPM much, and looses power in a matter of seconds.... you will notice that the engine is too cold because you can touch it and won't burn your fingers in a couple of seconds, and won't deliver it's maximum power (too rich).


It is important that you change one variable at a time, to track the problem!


Saludos

Jorge

Just another thougth.

Make sure also that your carb is fully seated and that the o-ring that seals the carb is in good condition.

The English manual calls for 0-15% nitro on all the engines...while italian version calls for 0-10% nitro.

As a general rule for all the engines...I wouldn't take it, I would try first and see what works best.

The more nitro in the fuel doesn't mean always more power, if the engine can't handle the nitro content so good. There are engines at their best at 5% nitro.

Saludos

Well that makes sense. I have an old ASP that says it will run with 0 to 15% nitro, but it will detonate and overheat on 15% anytime of year. It will run well on 10% in the winter, but must have 5% or lower in the summer.

how do you tell if its detonating? does it do something specific that screams detonation? maybe I just don't know what to look for.

In an extreme case you can hear the motor knocking or "pinging," but more often than not it will just overheat like in your case.

Here's another thing....you rebuilt the engine? Did you do a leak-test when you got done putting it back together? If there is exhuast gases escaping through any kind of gap in between the plug and the cylinder head, or the cylinder head and the sleeve.....it will get hot in a hurry.

Did you ever run a full tank of fuel through the motor on the ground at full throttle?

no leak test performed but I did "re-break in" the engine on the ground without issue. (without the cowl) But I've also run the engine on the ground with the cowl for a full tank without issue.

Did you ever hear a ping noise?
When you ran in on the ground....was it at full throttle?

If I were you I'd fly it without the cowling and see if that helps.

Write down the list of variables and start with the easiest, cheapest ones....and eliminate them as you go.

If it is detonating..you're going to have to lower nitro, lighten the prop load, or add a head shim or two.

What he said!!!
Start from the cheapest/easiest and work though it that way.
If you change a lot of things at one time you may fix it or make it worse not knowing what the result of each change is.
Getting a $20 temp gauge so you have more data to work with is important.
A lot of what we have to do is trial and error because we lack any real hard data.
Make a list of possible fixes/issues and then go down that list one after another, as has been suggested and you will find out what is happening.
Also check back and let us know what you find...
Good luck!

Never heard a ping noise, and i really don't thing that flying without the cowl will prove anything since I can fly it with the cowl without a problem, at least as long as I'm using an os plug, but doing that wrecked the ring last time without any real warning.

Luckily I have access to data recorders so I'm going to put a thermocouple on the head without the cowl on, run it till steady state, then do the same thing with the cowl on and download the data to my computer to analyze the results.

I'll share them when get a chance to actually do this,,, my in-laws are coming to visit this weekend...so there is no telling when I can try this.

flhyr,

Are you near San Antonio? I'm sure we could get you straightened out. There is so much stuff being thrown at you here, but it's usually something simple or a few small things.

Just going by the colors I've seen in the few photos, I can see it sure got hot. Two ways to go from there;
First, fuel-wise. When you are running at full-throttle on the ground you should be hearring a little bit of gurgling. That engine will wind out faster at speed in the air without the drag from sitting still and it requires more fuel for that. Some engines take that very badly. Also, try the lower percentage nitro and cooler plug next after you set it for the gurgling, or in addition to.

Second, making sure air gets over the engine, but I'm going out on a limb here and say that's not what is going on, at least not to such an extent as to see what we're seeing here.

Send me a PM, maybe we can get together if you're not too far away. I'd be happy to work with you on that.

Jimbo

Just tuning in..............

Looks like you are geting lots of info...good stuff....

I didn't see it mentioned before so I will share my experience with a ST .51 ringed...

Ran fine w/o any probs when level....
But point the nose up and errrp..... it would lean out and quit...
I even tried a perry pump....It would still lean out and quit.... no matter how rich.......
I tried everything......tanks, fuel line, differend sizes of fuel tubing (med, large, small) nothing made any difference....
I even placed ne ring, piston ect, from a dif engine (new stuff though) and made no difference.....

I Recieved a new ST .51 and no issues........................... ran great even when nose up....

Moral of this story.............
Sometimes you will never figure it out..

One more thing.....

I didn't notice any foam on your tank.....Believe me, it will
cause foaming and will cause a lean condition and then a dead stick.....

I think that telemetry system will shed some light for you....

Justin...

Well I appreciate the offer of help, unfortunately I'm in Dallas.

I do have foam under the tank, but it doesn't show up well in the picture.... but I did not have the foam there with the original tank and I'm sure it did not help. but I have had the issue with the new tank with foam, and have confirmed that foaming is not occuring by runing on the ground and observing the tank.

That being said.... who knows whats happening in the air.

What you said is so true...a lot of RC fans do not know that....and it is hard to convince them also!!! Capt,n

If a good Hesperian is telling you that, it must be true. Heya, Captinjohn! Take good care of my childhood summer village! And the White River...best fishing around.

I agree, running a low nitro content, ESPECIALLY in a ST, can work very well.

Jim

If it is slight it will sound like a rattle, and often only when the engine is accelerating up to speed. But often you won't hear a thing but the engine is unusually hot, looses power, and acts as though it is leaning out. Sometimes it won't detonate on the ground, or will only detonate on uplines because of the leaner mixture.

I have always been of the belief that the exit on the bottom of the cowl should be at least 2 times larger than the inlet (not as pretty but keeps it a lot cooler) from your photos I am not seeing this???

it also looks like your tank is not in foam. vibrations from the tank will put bubbles in the fuel tank and in the fuel line causing it to lean out

Yep, but since the picture was taken, I've enlarged the hoeles... probably not 2X the inlet still, but significantly more open now at the exit, still have the problem.

The tank has foam underneath it, but the picture does not show it very well. I don't have foam on the sides, putting some there may help me out. I alos have the tank very loosely attached, not rigidly... this helps alot to eliminate foaming too.

I'm hoping to get a run on the enine with a T'couple attached to the head tonight and will post the results.