Throwing a prop

Aug 19, 2011 No Comments by

Q: I have started the Thunder Tiger 91 mounted in the plane and amhaving troubles. With three different plugs tried (Two F types and one Fox Miracle Plug) and three different brands of 15% 4 stoke fuels being used, the motor dies when glow driver is removed and motor likes to kick the prop loose on start up (sarter or by hand cranked) I set the valve lash and checked the cam timing as per owners manual. This motor did this same act when mounted in a Great Planes Cub so it has never flown yet…Cam dot is at the top when key is way is straight up . Tank center line is just above the spray bar on carb and tank has a pressure line from muffler to over flow line. I am using a Alum smooth nut against the prop with a acorn scale-looking back up nut , a MAS 13×8 “K” prop on this Thunder Tiger 91 that is kicking the prop loose and dying when glow driver is removed. Again thanks !

A: If your Thunder Tiger throws props it is due to being run too lean or being over-compressed. Better check the head and make sure the head gaskets are in place. If so, then try adding  another .015″ gasket and reset the valves. As far as the engine dieing when you remove the starting battery – that’s a hard one to figure. This would be an indication of too cold a glowplug, insufficient nitro in the fuel or insufficient combustion chamber heat. As you have tried different plugs and fuel we can pretty well rule this out. How about the compression? is it low or soft? Other than this, I do not know what else to offer other than be sure the piston is actually at top center when checking the timing. Possibly the key way may be off.

Clarence Lee, Editors Blogs, Great Planes

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