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  #11  
Old 04-19-2017, 02:03 AM
DNeufeld DNeufeld is offline
 
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Location: Coeur d Alene
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If the fiber heel on Bendix mag points, or, points cam used on Slick mags wear, it does retard the timing. If the points (contacts) wear or burn away, timing advances. Or, the gap opens up, the points open sooner.
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  #12  
Old 04-19-2017, 03:06 AM
JamesClarkIV JamesClarkIV is offline
 
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Location: Gainesville, VA
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I carefully recheck timing after snugging down the magneto stud nuts to ensure it doesn't change as I tighten. That is not the problem.

Drift and reset only occurred once between 50 and 96 hrs (2 and 4 degrees). However since I didn't time them when the engine was new, there may have been an additional amount of internal wear/drift that I corrected externally but not internally at the 50 hr mark in addition to what I know about between 50 and 96 hrs.

I'm familiar with the mixture sweep during hot start and again do not suspect starting technique is the culprit. Strongly suspect what Scott said with weak spark due to less than optimal e gap angle that has only been retimed externally. Does anybody know how far in degrees a slick cam or points have to wear before a noticeable drop in starting performance is experienced?

An earlier post says if it runs ok after start weak spark is not the problem but every thing seams to scream weak spark.

Here is a link to inflight LOP mag stress test if it helps around minute 38
https://savvyanalysis.com/flight/182...d-68b6812d2a16
My first attempt at doing this test.
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Last edited by JamesClarkIV : 04-19-2017 at 03:09 AM.
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  #13  
Old 04-19-2017, 04:27 AM
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rzbill rzbill is offline
 
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Location: Asheville, NC
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Jim,
I have 600hrs on my M1B. I had early timing drift of a few degrees on both mags. Adjusted that out first annual. I had checked it prior to first flight.

In regards to knobology. Early on, I tried unsucessfully to perform hotstarts as others have described elsewhere, not just this thread. My assumption is that mine boils the fuel so well that it is starving for gas when I get in the cockpit. I am unable to hot start my M1B unless I force it to the rich side of the mixture sweep by giving it approx 1 second shot of fuel before cranking. I turn on the boost with mix at ICO. Mix in then out. Crack throttle and crank. Usually catches in 6 to 10 blades. Worst case if I flub it is to stop. Wait 30 sec or so for the starter to cool and repeat procedure. Pretty rare for that.

Spark plug maintenance makes a difference.
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Last edited by rzbill : 04-19-2017 at 04:37 AM.
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  #14  
Old 04-19-2017, 06:14 AM
dlloyd3 dlloyd3 is offline
 
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Not always an install problem. At the flight school at 8A6 we had two Slick impulse mags fail at about 150 hours with similar symptoms. Both replaced under factory warranty.
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  #15  
Old 04-19-2017, 06:56 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by Bicyclops View Post
I always thought that points wearing retards timing. The fiber heel that rides on the cam wears and lifts the points open a little later. Do I have that wrong?
Sorry. I was thinking of point wear and in my haste applied the same concept to cam/block wear. Wearing points cause the assembly to close tighter. This brings the block closer to the cam center. In this case, the cam lobe will start acting upon it earlier in the rotation, therefore advanced. This is because the block is moved closer to the center of the lobe (shorter radius).

A worn lobe or block will retard the timing for the opposite reason.

Larry
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  #16  
Old 04-19-2017, 07:07 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by JamesClarkIV View Post
An earlier post says if it runs ok after start weak spark is not the problem but every thing seams to scream weak spark.
I thought about this a bit more. While my statement is generally correct, I was not thinking about the impulse mag. Generally speaking a spark is a spark and as long as it is strong enough to light the charge, greater strength doesn't make it any better. However, a stronger spark will help light very lean or very rich mixtures that a weaker spark might fail to light. This would impact the fringe situations during your start but not overly noticeable. It might take a bit more cranking, but you should eventually get to a normal mixture and it will fire.

Mags don't produce a lot of energy at low speeds. That is why they have impulse couplers. If your spark energy is on the lower end, but adequate while running, it may be inadequate at starting RPMs with the impulse coupler, due to the lower RPM. I don't know how fast the impluse spins the shaft, so couldn't say this is true or not, but worth looking at.

No doubt having an optimum ignition system is always a good idea and something you should strive for. Can you hear the impulse coupler snap as your rotate the prop? A failed impulse coupler would greatly reduce spark energy during cranking and cause starting problems.

Also, have you checked your spark plug gap recently?

Larry
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Last edited by lr172 : 04-19-2017 at 07:30 AM.
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  #17  
Old 04-19-2017, 07:11 AM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by JamesClarkIV View Post
I'm looking for help understanding my hot starting problem. I'll give as many details as I can here and respectfully solicit your thoughts and recommendations...
Can you describe the immediate post hot start behavior of the engine? Is it typically fat, as evidenced by a "soft" light off, smoke and rough running on less than 4 cylinders, or does it exhibit cold start behavior such as rapid light off and immediate smooth running on all cylinders?

Knowing the difference will point to mixture or something else.
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  #18  
Old 04-19-2017, 09:53 PM
JamesClarkIV JamesClarkIV is offline
 
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Although I don't see smoke, it seems to be different from a cold start and rough running just post hot start.

I pulled all 8 spark plugs today to look at them. The top four were new tempest installed at the 96 hr mark. They looked ok and measured a gap around 0.021. I gapped them to .016 and reinstalled with new copper washers.

The bottom ones however were champions installed since new and I noticed that two of the four had junk deposits in them between the ceramic and the outer casing deep down in the inside of the plug. One other had a very large hard buildup higher on the ceramic just below the electrodes connecting the ceramic to the casing. It looked like a horizontal salagtite and I'm guessing was shorting the plug. This was bottom of cylinder 2 which is the left impulse coupled mag. The last of the bottom plugs looked normal. I replaced all bottom 4 with new tempest plugs.

Haven't run yet but have hopes that this will help.

Does this mean I need to be even more aggressive with the leaning during ground ops?
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Last edited by JamesClarkIV : 04-19-2017 at 09:56 PM.
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  #19  
Old 04-19-2017, 10:07 PM
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Toobuilder Toobuilder is offline
 
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If you are grinding on the starter for 15 seconds, the engine wheezes to life and is rough as a cob for a while, then that is indicative of a flooded condition. I'd recommend staying off the boost pump no matter what the fuel pressure says, and assume that the engine is flooded if it has sat for 15 minutes to 4 hours after flight. Follow the flooded engine, clearing proceedure: ICO, no boost, throttle open 1/4, starter, and sweep the throttle open. If no fire after 5- 10 seconds, then the engine is cleared and you can give it a small shot of prime and try again.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
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  #20  
Old 04-20-2017, 06:25 AM
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Danny King Danny King is offline
 
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Default HOT STARTING

Shutdown
1) Mixture off
2) Battery off
3) Ignition off

Hot Start
1) Battery on
2) Ignition on
3) Throttle crack
4) Starter engage
5) After start mixture rich

Do Not turn on boost pump!
Do Not advance mixture until engine start!

With Electronic Ignition (i.e. Pmags)
1) If no start in normal cranking time
a) Mixture rich
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Last edited by Danny King : 04-20-2017 at 06:44 AM.
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