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-   -   Unhappy Result on First Engine Start (https://vansairforce.net/community/showthread.php?t=114464)

Walt 06-30-2014 06:47 PM

I agree that a few degrees is probably not the culprit, if the engine is not cranking "vigorously" enough (prop should spin rapidly with no hesitation on the compression stroke) that is when a kickback usually occurs. Slow cranking = kickback.

erich weaver 06-30-2014 08:46 PM

I have an IO-360B1B with 9:1 compression ratio, dual p-mags, and a Whirlwind 20RV prop. I had occasional kickback problems, typically on occasions requiring a 2nd start attempt. My ring gear is missing one tooth as a result of one episode.

Per emagair, the combination of their ignition with a lightweight prop, high compression, and low starting rpm can result in kickbacks due to the spark firing at TDC. Makes perfect sense to me. The easiest thing to change is to retard the timing by a few degrees. Secondly, if a 2nd start attempt is necessary, keeping the p-leads grounded for a few spins of the prop during start up insures your RPMs are maximized before the first spark event, minmizing the potential for kickback. This is not necessary for first start event due to the Run Mode Star Delay, which accomplishes the same thing. RMSD does not occur for subsequent start attempts unless you power down, which I prefer not to do. Your choice though.

I agree that slow cranking can be the problem. Obviously a run down battery will lower your starting RPMs and increase your chances of kickback. Other than having a well maintained battery however, you don't have much control over how fast your prop will spin when starting. The battery was not the issue in any of my episodes. A few degrees of retard in the timing CAN make a difference. Emagair says so, and so do I, because it worked.

Erich

jpharrell 07-07-2014 08:16 AM

Success
 
I thought I should report back with the outcome of the second attempt to start my engine. After replacing the ring gear and resetting the static timing to 1.5 teeth (3.5 degrees) after TDC I cranked the engine up Saturday with success on the first try. Oil and fuel pressures were in the expected ranges and the temperatures were climbing as expected during the three minute run.

A link to the video is below.:)

https://www.youtube.com/watch?v=X4rcYkZ6oIY

MarkW 07-07-2014 09:13 AM

Good news John, glad to hear it.

andyg 07-07-2014 10:53 AM

I like happy endings! :)


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