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Some progress with the GT80, but still a couple of concerns.

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Some progress with the GT80, but still a couple of concerns.

Old 09-09-2015, 04:59 PM
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LGM Graphix
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Default Some progress with the GT80, but still a couple of concerns.

So for those of you who have followed my past GT80 post, somehow I have made some progress.

Here is the rundown.

I cleaned the carb.

Removed a fuel filter that was to small

Checked the plugs, checked all wiring etc.

As I posted before, it ran once, very poorly, 4400rpm. Did the above things. Then most recently I had zero spark, none, zilch, zip, zero......

Fast forward to yesterday, out of frustration I go over to the airplane, and spin the prop with the electric starter again with the plugs out. This time there is spark........ Haven't done anything at all, but now there is spark..........

So today I decide to see if it will run.
It took about a dozen tries, but it finally fired. Not only that, I was able to get up to 6100rpm. Couldn't get any better than that but that's a fair bit better than 4400.

Questions/concerns are:

Stock engine, stock mufflers, Mejzlik 24x10 carbon prop, NEW engine, this is only the 3rd run ever on it, what RPM should I be seeing at this point? I keep reading 7000 - 7200 with that prop BUT I don't know if that is with stock mufflers, if that is broken in or how much rpm gain I will see after break in.

Bigger concern is this. Both cylinders are spitting some oil out of the exhaust, that doesn't concern me in itself EXCEPT the right cylinder is spitting out 10X what the left cylinder is. The right wing panel after a 10 minute run between idle and full throttle is covered in oil while the left only has a little bit.

Does this engine just need a few tanks run through it? It was idling very nicely, transition from idle to full power seems very slow to me but I'm not used to gas engines and don't know how fast it should be when you hammer the throttle, I would say from idle to full power if I hammer the throttle it takes 2 seconds to get to full rpm.

Fuel is mixed 32:1 at the moment.

Thanks in advance
Old 09-09-2015, 05:25 PM
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Truckracer
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Regarding more oil from one cylinder than the other ..... every twin will run a bit richer / leaner on one side than the other. Its only an issue if there is a major difference.

Regarding the performance, 6100 is getting there but still low. I'd suggest this is probably due to the stock mufflers more than any other factor if you have the top end (H) needle leaned fairly close to peak RPM. With that prop you might see performance in the 7000 range but only with aftermarket mufflers and after breakin.

So what would I be looking for with your prop and stock mufflers ..... maybe 6500 to 6700 or so on a good day with a good tune. People who report readings well into the 7000+ range are doing it with less prop load which may be a different design prop rather than a different size prop. Prop load varies considerably between brands even when comparing the same size props.

My favorite GT-80 / 445 prop for aerobatic or Warbird use was the Menz 24-10 which was really a 23.5 - 10 and I typically expected to see 6900 to 7100 or so RPM. The long since discontinued Bolly 24- 10 wood was also a good choice. Current Xoar 24-10 wood props will be several hundred down from the above numbers as they are a higher load prop than those mentioned above.

Back to oil on the airplane .... is it clear oil or dirty exhaust oil? I ask as these engines always have a bit of fuel spray from the carb due to being piston ported engines and sometimes this finds its way to the outside and is confused as being exhaust oil. A ram air horn or carb ext. on the carb will reduce or eliminate this spray by allowing it to be be re-ingested by the engine before it escapes in the airstream. Keeps the firewall area much cleaner also. This problem is one I really don't like about the GT-80 and one major reason I no longer fly one.
Old 09-09-2015, 05:43 PM
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Hi truckracer,
I went with the mejzlik prop as that is the one I read multiple times to be the best on that engine and getting into the 7000 rpm range.
The oil I'm seeing is dark brown coming out of the exhaust for sure. I will run another tank through it tomorrow and see where it's at.
Old 09-12-2015, 06:21 AM
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dirtybird
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If you are now getting spark and didnt before I would suspect an intermittent open somewhere. On my G62 the plug leads just are pushed into the coil. I don't know if the twin has the same arrangement. You should check that though. An intermittent problem nearly always will come back to bite you.
Old 09-12-2015, 01:42 PM
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Intermittent electrical problems are a real bugger to find.
I pulled my hair out with one engine which was fantastic one day and wouldn't start the next.
After wasting numerous trips to the field I got fed up and pulled off all the ignition components, wiring,hall sensor, everything. Put all new stuff on and BAM different engine.
If I were you a electric ignition would go on it.
http://www.rcextremepower.net/ZenoahIgnitions.html
Old 09-13-2015, 06:39 PM
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Using the magneto style ignition it needs too turn at about 600rpm to get ignition (spark). it is different than an electric ignition. I have used zenoah for 25+yrs now. They build a rock solid engine ( bulletproof). I have 8-10 of them in planes. Stock exhaust will hold it back 3=400 rpms Drill the insides of them out going through the exhaust and port hole , and after a few tanks it will loosen up some and you will see another 3-400rpms.
The GT80 will do its best at 8000-9000rpms it likes the high RPMs . If you can get it to tach at 7500 on the ground it will scream trough the air.
Old 09-13-2015, 07:13 PM
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With what prop will you see 8000+ on a stock gt80? 7000 is the number I keep hearing with a 24x10
Old 09-14-2015, 09:27 AM
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I use a 24x8 or 24x6-10 Zinger. They are cheap and work fine for my needs. The same with a G62 use a 22x8 they are screamers. I have only lost one conrod in 25-30yrs . One G62 I have is 20+yrs old with at least 100hrs on it and I flew it last week, strong as the day it arrived.

This past year I bought 3 of the DLE engines 35ra, 55ra and 85, figured I would give them a try and so far
2 have run OK (35 inconsient carb adjustments) 55 has been running steady and the 85 had one flight then the ignition sensor broke.

Zenoah may be considered old and heavy but I believe strongly in them never any problems , they just run.

Last edited by TimD.; 09-14-2015 at 09:34 AM.
Old 09-15-2015, 08:42 AM
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JeffH
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For hand starting....all three magnets in the flywheel have to pass over the pick up at XXX RPM to fire. It is an odd feeling to start by hand since you have start your flip when the engine is not on compression yet. Flip like you mean it!!
I had other suggestions here, but you already covered them in the other post.

Check the head temps from one side to the other, other than that, it may be time for a trip to Ralph.

Last edited by JeffH; 09-15-2015 at 08:56 AM.
Old 09-15-2015, 11:33 AM
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Pop some holes in the muffler baffles and you will see a difference. One cylinder usually runs a bit cooler and residue will come from it , that is normal.
As for starting , this has always works for me but I am at sea-level. It should have a spring starter. First choke, then spin the prop 5-7 times by hand to get fuel in the carb zenoah likes to be wet. Then spring start once you should hear it pop off, then take off the choke, spring start it and off you go.
Old 09-16-2015, 03:21 PM
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Little better today. Saw 6200. Here is a pic of the oil from the right cylinder.
Old 09-16-2015, 03:22 PM
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Ok. Can't upload from my phone. I'll upload when I get home....

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