Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Dang GRRT quiting in air

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Old 11-09-2002, 06:25 PM
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FlooredCOBRA
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Default Dang GRRT quiting in air

Well I just got back from flying a few minutes ago. My DD flies great but my GRRT is acting up.

When I run up to WOT I notice that it runs okay but when i tilt nose up it starts to die like it is lean. So I richened it up some and still the same thing. While running i could see that I had some fuel leaking from my engine head on the right side. Not good! So I tightened it up and the engine ran perfect. Seems that was my problem. So I ran it a bit more on ground and noticed head was a bit loose again. So I re-tightened it again and it ran good.

I refueled and decided to get into the air. It flew fine until about a half a tank was about gone then it tarted acting up again. The engine would rev up and down, up and down. It would not maintain steady rpm's in air. I guess my head came loose again. I shouldn't have even flown it then.

At first I thought I ran out of fuel but that would only make it a 2 minute flight. So I checked when in ground to see and I still had some left over. So all I can think of is I need to take the screws out and put some thread lock on them. I was running 15% fuel because I was trying to finish what little bit I had. One thing I wonder is the nitro to high and causing it to leak? I do have a full bottle of 5% here that I start using since I am out of 15%. But I was wondering if this is what made the head come loose. I know some people say you need to shim the head with higher nitro. Is this what happens when to much compression with that kind of nitro?


Anyways I when flying after the engine died in air I had to land right away. Which I hate! I like to plan my landings. It cam in hot and bounced off field and did a cartwheel. I did not do anything to it but put a small pin hole on my right wing. Which I cant stand also because now I have to patch it. So guess I will pull the covering off and redo the wing tip again. Not sure yet.

So anyways. do you guys pull the head off when engine is new and apply thread lock on them? I guess I should have to prevent this from happening. Also learned not to dang fly until I am ready and have kinks worked out. Cant stand when someone keeps on going " common man just fly it" Little do they know the investment in time and money in one of these things.

Oh well we all learn.
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Old 11-10-2002, 02:52 AM
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Default head bolts

Had same problem with my jett 60. Spit out head bolts nearly every run. Burned head shims because of combustion leak, warped head and cracked head button. I was told to check them every flight and not to use thread lock. Make sure you tighten in a star pattern like putting on a tire.
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Old 11-10-2002, 04:43 AM
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Default no lock tight?

okay so do not use lock tight? Now that is odd. My head screws are loosing at after every flight but right in the middle of it and causing the engine to die. Also on the ground if I run it a bit they loosen and I can see the leaking. This is a very annoying problem and Tightening every flight I dont think is going to cut it.

Out of curiosity how come no thread lock?

Just looking on how to cure this problem.
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Old 11-10-2002, 12:05 PM
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Default Dang GRRT quiting in air

use some diamond tape to solve your hole, mines covered in the stuff now.. my MVVS ( not a GRRT ) also leaks, from the bottom, not the head, but after using some gasket suff it still does it, but seems ok, so i let it be. maybe the GRRT is like the rest of the range and dosnt like high % nitro, too much bang in there
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Old 11-10-2002, 06:31 PM
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Default Engine quitting

This may not be the answer but it may be worth a look. Is your carb seated firmly on its gasket?

I remember I had a GMS 76 I could never get to run right, lousy transition and quitting in flight. In trying to get an existing throttle linkage to work I loosened the carb and rotated it a bit to get the throw right. I never pressed the carb down tight before tightening the screw. I sent that engine back and forth for service several times and nobody could figure out what was wrong with it. Finally it just dawned on me one day and once I seated that carb tightly it ran perfectly. There must have been a tremendous amount of air leaking around that gasket.

Before my GMS problems I owned an MVVS 50 that would never run right either. I recall the engine came with the carb separate from the engine. I sold it before I bought the GMS so the idea of tightly seating that carb never came to mind. After my experience with the GMS I suspected it was the same problem. I probably never seated that carb tightly on the gasket when I installed it.
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Old 11-12-2002, 06:44 PM
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Default Dang GRRT quiting in air

Too much compression for the nitro content equals pitting in the cylinder head and piston! Not a good thing!! It also makes the engine run "less than perfect" , as you are experiencing; the timing and compression is set up to run 0% nitro. Anything more and you need a shim or two. Call up MVVS..they will send you some shims.

As for the head bolts working loose, I've had to tighten mine once in a while, but not like you are having to. I just check all the bolts once in a while. Vibration is my suspicion; is your prop balanced WELL, not just "close enough"? When you're spinning something over 20,000 times per minute, any little imbalance is REALLY magnified. When you tighten the bolts, do as somebody metioned earlier: do a star pattern like changing a tire. After you tighten all the bolts once, go through and do it again..you will be surprised when you are able to tighten them some more!

Just curious, where do you have your pressure tap on the pipe? I was told right at the fattest section. That's where mine is and it runs great.

Good luck!

Carl
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Old 11-13-2002, 05:51 AM
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Default Dang GRRT quiting in air

I have my tap on the fattest part of the pipe and right before it tapers down to the front of pipe. Supposedly this is the optimal part to place it at.

I havent really tried 5% fuel yet but hopefully this will help my problem with the compression
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