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Model Forum / Radio Controlled / Air Models / July 2006Question for the engine gurus....
I have, at last count, something like 23 Super Tigre engines (all but two or three made in Italy). With a few, mostly four-stroke-powered exceptions, my air force is primarily ST powered. I take pride in my engine tuning ability and all my two-stroke engines will most always start with just a quick twist of the spinner between my thumb and forefinger. I've been keeping two G34 Heli (ringed ABC) engines on the shelf for use in a twin. These engines make power close to a typical .40 while weighing 12 oz.. I decided to put them in a Hobbico TwinStar and get some twin experience before I build my Wing Mfg. A-26 Invader. I cannot get one of the G34s to run properly. It won't come within 500-600 RPM of its sibling and responds vaguely to the needle settings. When run at full throttle and set rich, it responds to leaning of the high speed needle and peaks for a second, then slows. I wouldn't describe it as sagging though, and after I quickly richen the mixture it doesn't come back up to speed. I suspected some kind of fuel system problem. I removed the offending engine from the TwinStar and mounted it on my break-in stand. Same performance. I checked the backplate and carb for air-tight fit. I disassembled and cleaned the carb. I replaced the glow plug. I swapped out the muffler. Same performance. I even swapped out the whole carb. No difference. What should I be looking at next? I'm really bummed because it's hard to find the old G34 Heli engines. If I can't get it to run properly, I'll have to buy TWO of the current G34 Aero engines. Good flying, desmobob >I have, at last count, something like 23 Super Tigre engines (all but two >or three made in Italy). With a few, mostly four-stroke-powered [quoted text clipped - 26 lines] > Good flying, > desmobob But the same thing could happen with the new engines, Desmobob, so you wouldn't be any better off. If you use a computerized Tx, you can adjust both engines at WOT, then slow down the faster of the two electronically with the volume control. Perhaps have one memory with both throttles wide open and another memory with the faster engine slowed to come close to the slower engine. Just don't try to match the engines by richening up the faster engine. But you knew that...<G> Ed Cregger >>I have, at last count, something like 23 Super Tigre engines (all but two >>or three made in Italy). With a few, mostly four-stroke-powered [quoted text clipped - 37 lines] > don't try to match the engines by richening up the faster engine. But you > knew that...<G> I agree with you here, Ed. Many people believe that one engine "should" peak at the same rpm as another. The way we have always tuned twins is ; tach them both, then richen up the one with the higher rpm to match the slower one. I think he is trying to "force" the slower one to give more rpms. > But the same thing could happen with the new engines, Desmobob, so you > wouldn't be any better off. [quoted text clipped - 5 lines] > don't try to match the engines by richening up the faster engine. But you > knew that...<G> Your plan sounds very practical, Ed. It would be easy to adjust the travel volume to slow the good engine down to the speed of the "bad" one. I'm really not at all happy with the way it runs, though. I suppose it COULD be a matter of that engine having tolerances on the far end of things, and a longer break-in may be required. The strange thing is that I break in all my engines on a dedicated break-in stand, and I don't remember that engine acting up when I first ran it. It likely has 36 oz. of fuel through it on the break-in stand, and another 16 oz. through it while mounted in the TwinStar. I would think it should be settled down by now. I mounted the offending engine in the TwinStar again and changed the fuel tubing for good measure. I'll run it some more and see what happens. And I'll use my radio's ATV adjustment to get the engines closer to synch. Thanks, desmobob >> But the same thing could happen with the new engines, Desmobob, so you >> wouldn't be any better off. [quoted text clipped - 24 lines] > Thanks, > desmobob One thing I have noticed when running two glow engines on a model airplane is that the aggregate vibration effects of both engines running usually makes one of the engines change its mixture some. Especially when running "eggcrate" constructed wings (Falcon 56 type construction - not D tube). I've seen this on a couple of different models over the years. But, admittedly, this doesn't appear to be your problem. If piston rings are available, just for hoots, I'd change out the ring in the slow engine and start the break-in all over again. I agree that with 36 ounces plus of fuel through the engine, it should be broken-in enough to have shown signs of improvement by now. I wish my two G-34 ringed engines were the ABC models like yours. Oh well....<G> Ed Cregger > If piston rings are available, just for hoots, I'd change out the ring in > the slow engine and start the break-in all over again. I was considering that. I'll have to dig through my parts bag to see if I have a spare ring for it. I'm now wondering if the ring is the same for the Aero and Heli models. And I'm wondering what the odds are that'll I'll break it during installation. :-) > I wish my two G-34 ringed engines were the ABC models like yours. Oh > well....<G> Be careful what you wish for! Thanks again for your suggestions, Ed. desmobob >> If piston rings are available, just for hoots, I'd change out the ring in >> the slow engine and start the break-in all over again. [quoted text clipped - 3 lines] > the Aero and Heli models. And I'm wondering what the odds are that'll > I'll break it during installation. :-) I just dug through my parts bag and guess what I found... A G34 Heli piston ring. :-) (And I ordered another one from Tower today. They list the part as being for the G34/G34 Heli) >> I wish my two G-34 ringed engines were the ABC models like yours. Oh >> well....<G> And guess what else I found... A G34 Heli cylinder liner! Will installing that chrome-plated liner in my G34 Aero make it a G34 heli? I might just have to find out! That would give me a third G34 Heli and a better chance to get two compatable engines for my twin. I'm finally glad I spent so much time and money buying up a bunch of old Italian ST parts when Tower was phasing them out in preparation for ST moving to Asia. Good flying, desmobob Is excess oil coming from the front bearing behind the prop washer, suggesting an air leak there? Is any black crud coming out of the exhaust, suggesting that either it's not yet broken in or it's eating itself up internally? Ringed engines can take a while to break in well. The "bad" one may just need some more rich run time. Also, are the head bolts evenly tight? An ounce of distortion can create a pound of poor running. >I have, at last count, something like 23 Super Tigre engines (all but two or >three made in Italy). With a few, mostly four-stroke-powered exceptions, my [quoted text clipped - 28 lines] > > > Is excess oil coming from the front bearing behind the prop washer, > suggesting an air leak there? Is any black crud coming out of the [quoted text clipped - 3 lines] > bolts evenly tight? An ounce of distortion can create a pound of poor > running. There's no oil seepage, black gunk or any other indicators. The head bolts have been checked and I even replaced the head with another brand new part I had in my "Big Brown Bag O' Super Tigre Bits" ! :-) I need to meet this problem Italian style... I'll fire up the espresso machine this weekend and get serious.... Thanks, desmobob Did you tell us what fuel you are using?? Frank Schwartz > Did you tell us what fuel you are using?? No. :-) But I will! It's the same 10% nitro, 18% lube with a big splash of Klotz castor I've always run in all my STs. The other G34 seems to enjoy it. And I checked to make sure both engines had the same head gasket/spacer in place to be sure one wasn't enjoying the nitro more (or less) than the other..... Good flying, desmobob > I have, at last count, something like 23 Super Tigre engines (all but two or > three made in Italy). With a few, mostly four-stroke-powered exceptions, my [quoted text clipped - 19 lines] > plug. I swapped out the muffler. Same performance. I even swapped out the > whole carb. No difference. How long have they both run for? My mate had a pair of OS 32s on a twin-converted World Models World Star 40 trainer, and they were a bugger to get tuned to each other, and would vary greatly as the plane moved about - for the first 10 or so flights one engine would always deadstick no matter what we did. However over a fair bit of time they settled down and now run much closer to each other and behave a lot more consistently in the air. So maybe you need to run both in a bit more? > How long have they both run for? My mate had a pair of OS 32s on a > twin-converted World Models World Star 40 trainer, and they were a bugger [quoted text clipped - 8 lines] > need > to run both in a bit more? I'm really hoping this is the case. The "bad" engine is just acting too funny though; not what I would think was just a lack of sufficient break-in time. But this IS my first experience with the two-stroke ringed engines using chrome-plated bores... though I've broken in five different ringed, chrome-bored four-strokes (Saitos). Good flying, desmobob A friend had a G-34 where the secondary needle was incorrectly assembled at the factory ..... but you have swopped carbs? I had an S45 five years ago - tried 2 other non ST carbs, 2 silencers, various plugs and fuel - never could get it to run right at 60% throttle. It often quit at this point. Another friend has an S51 that runs as sweet as anything ..... One tip I was I was given was not too push the exhaust stub too far into the silencer. Not sure if ST's are best run on low nitro fuel? >I have, at last count, something like 23 Super Tigre engines (all but two or >three made in Italy). With a few, mostly four-stroke-powered exceptions, my [quoted text clipped - 26 lines] >Good flying, >desmobob >A friend had a G-34 where the secondary needle was incorrectly > assembled at the factory ..... but you have swopped carbs? [quoted text clipped - 9 lines] > > Not sure if ST's are best run on low nitro fuel? The biggger ones do I think. mk >>I have, at last count, something like 23 Super Tigre engines (all but two >>or [quoted text clipped - 36 lines] >>Good flying, >>desmobob >A friend had a G-34 where the secondary needle was incorrectly > assembled at the factory ..... but you have swopped carbs? Yes... I switched the carbs between the two engines and the "bad" one didn't improve. > One tip I was I was given was not too push the exhaust stub too > far into the silencer. That's a good tip. I always make sure they have plenty of room to let the exhaust get out. Sometimes I even shorten the exhaust stack to I can get plenty of breathing room inside the muffler without having to have it mounted out so far. I had noticed there was a slight difference between the mufflers on my two G34s. I even tried swapping the mufflers. No change. > Not sure if ST's are best run on low nitro fuel? They start to snap and crackle on higher nitro fuels. I found that 5% and 10% works great in the small engines. Good flying, desmobob |
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