ORIGINAL: Capt. John
ORIGINAL: proptop
I had an engine pop and catch my knuckles...without any glow battery attached [X(] The catalyitic (sp?) reaction of the alcohol with the Platnum element of the glow plug I'm guessing?
Whenever I attach the glow plug battery I make sure the piston is at BDC or at least not closing/ trapping any vapors in the cylinder...along with keeping the hands well away from the prop.
My guess Capt. is that the piston was part way up (or down) in the cylinder, and just the right mixture of fuel/air was trapped in there and it ignited when you attached the plug battery.
Proptop....You've made an interesting point here, although I'm not sure I understand all of what you're saying. This could change my start up procedure.
I don't know what you mean by "piston is at BDC" (Before Dead Center?). Are you referring to the point when there is loose play in the propeller, as apposed to when it's tight (during the compression stroke)?
Please explain further.
If your saying that the engine won't self start if the propeller is "loose", but it could if it's in the middle of the compression stroke, "tight", then the ignitor shouldn't be attached unless the propeller is "loose". THEN attach the ignitor, take hold of the plane, and turn the propeller to the beginning of the compression stroke with the end of the starter, and hit the starter button to spin the prop and start the motor. The free hand could be used to hold the loose propeller as an additional precaution, as suggested by a couple of respondents here.
Capt. John...I don't know how I missed this? (sorry ) You got it...and Phil also did a pretty good job of explaining what I meant as well...(thanks Phil )