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

Engine Problems

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Old 04-22-2003, 10:52 PM
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Chap
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Hello everyone,

I need some advice with with a recently completed Balsa USA Scrapper.
The first flight with the model was with a Fox 40 Delux, 10x6 Master Airscrew prop and Wildcat 10% nitro 16% oil fuel. During the first flight the plane easily exceeded 100 mph however the glow plug blew which resulted in a deadstick landing. The engine was hot.
I allowed the engine to cool and replaced the plug with a Fox standard long with idle bar. I richened the top end to about a 200 rpm drop. The plane flew the next two flights at half throttle, however the engine still ran warmer than usual. The fourth flight I replaced the Master Airscrew prop with a 10x6 APC and leaned the top end back towhere I normally run (50 rpm drop). Again the Scrapper exceeded 100 mph and the glow plug blew.
The engine has been on numerous airframes and have never had a problem in the past. The props were both balanced and the fuel tank is set in foam. Any ideas?

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Old 04-23-2003, 03:01 AM
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FlooredCOBRA
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I seem to think it may be on the rich side still. I would just richen it up and do the pinch test.

Another thing to check "just in case" is your fuel lines & tank. Check to see if your fuel line with clunk does not have a hole in it and is still attached inside tank. Also trace your fuel lines to make sure you don't have a small pin hole in it also. That can cause it to lean out and heat up.

Also is the engine in a cowl? if so that would also make it heat up if proper cooling vents was not cut out.

If not it sounds a bit confusing being that you had the engine run good on other planes.
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Old 04-24-2003, 12:23 AM
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Chap
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FlooredCobra,
Thanks for your thoughts. The tank is brand new, I will check to make sure no holes. Yes the engine is cowled. The carb up is exposed to the airstream, the crankcase is completely covered. Should I get some air past the crankcase?
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Old 04-24-2003, 02:21 AM
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FlooredCOBRA
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I am not sure what it could be then. Sounds a bit odd. Usually the crankcase heat does not need to be dissipated as much the head of the engine.

How many gallons do you have through this engine?

And have to taken the head off the engine at any time?
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Old 04-24-2003, 08:53 PM
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Chap
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I bought the engine new in 1991. It has never really been used much at most maybe 3 gallons of fuel through it. No the head has never been off.
I am going to remove the engine and put a TT46 Pro on it. I have had excellent luck with these engines.
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Old 04-24-2003, 08:59 PM
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FlooredCOBRA
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Default Got an idea!

Hey since your taking it off send it this way!

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Old 04-24-2003, 11:31 PM
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Blowing Glow Plugs is a sign of a Lean Run, or an over compressed engine.

Double check your low and high speed needles. With a Fox, I would aim for at least a 500 rpm (not 50) drop from peak. Also, 16% oil may be a bit on the low side for this engine, I would suggest a minimum of 18% and preferrably 20%.

If none of this works, consider adding a 3-5 thousandths head shim.
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