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  #1  
Old 04-18-2017, 06:40 PM
JamesClarkIV JamesClarkIV is offline
 
Join Date: Feb 2011
Location: Gainesville, VA
Posts: 49
Default Magneto Timing Drift & Hard Hot Starts

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.

IO-360-M1B
Impulse coupled slick magneto on left side
Non impulse coupled magneto on right side
200 hours since new

Neither magneto was timed prior to first flight, used whatever I got from Vans/Lycoming with the new engine. None of the plug gaps were checked prior to first flight...chalk it up to ignorance on my part.

Around 50 hours, I learned how to time the magnetos externally and set each to 25 BTDC. Between 50 hours and 96 hours, I noticed that hot starting was progressively getting more difficult, cold starting more or less ok. At 96 hours, I checked the mag timing and found one to have advanced 4 degrees to 29 BTDC and one to have advanced 2 degrees to 27 BTDC (unfortunately i didn't think to record/see which drifted more: right or left). Neither appeared to be loose and I don't think they drifted in their "external" timing wrt the engine. Also, during this time I began the hunt to lower CHTs with better baffle seals, etc, striving for the never higher than 400 F. I retimed both mags externally by loosening the mounting stud nuts slightly and shifting the mags 2 and 4 degrees respectively to return both to 25 BTDC at the 96 hr mark. I also checked and gapped 8 spark plugs for the first time at the 96 hour mark. Many were > 0.022 so i decided to replace 4, and regap 4 to .016. immediately noticed lower CHTs and seemed to have slightly better hot starts, but not great.

At 135 hours (1st annual), I rechecked the magneto timing and found that they were both still at 25BTDC (no more "internal" drift). I also verified neither was in the magneto recall SN range. I see that if it drifts more than 4 degrees I should IRAN, but haven't done that yet. I had wired my two ignition switches to only allow the starter button to operate when left mag was on and right mag was off. After many hours of experimenting, I noted that after cranking a few turns and getting a few pops, I could flip on the right mag switch during cranking (which killed the starter) but sometimes caused the engine to start.

Now at 200 hours and springtime, my hot starts are getting darn near impossible without 15 seconds of cranking and 5 or 6 attempts. Using the crutch of flipping on the second mag when the engine coughs, doesn't seem to help much any more.

I've tried a variety of techniques that I have read about here for starting after a short < 1 hr lunch stop, but I'm convinced it is a weak ignition, not plugs, not mixture, not knobology technique during start. I don't have a purge valve and not too interested in the work to install one.

At this point, my hot starting issues are really dragging me down to the point of causing huge alternator charging loads after getting started, and excessive wear on the starter. I'm quite interested in getting a single EI to replace a mag as I think this may help my starting (#1 goal).

What am I doing wrong; what should I be exploring further?
Should I remove/open my mags and reset the e-gap? Can I learn this by reading or need someone to show me?
Should I remove one and go direct to EI?
Your thoughts are much appreciated.
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Jim Clark
2015 RV7A
Manassas VA
Aircraft Blog: jamessclarkiv.com

Last edited by JamesClarkIV : 04-19-2017 at 03:14 AM.
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  #2  
Old 04-18-2017, 07:01 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 4,596
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Are you sure the wires aren't crossed? E.g., right switch actually turns on left mag?
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  #3  
Old 04-18-2017, 07:08 PM
JamesClarkIV JamesClarkIV is offline
 
Join Date: Feb 2011
Location: Gainesville, VA
Posts: 49
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Bob, Thanks for the thought, but no, I'm pretty certain we have checked that carefully several times.
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2015 RV7A
Manassas VA
Aircraft Blog: jamessclarkiv.com
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  #4  
Old 04-18-2017, 07:17 PM
F1R F1R is offline
 
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Location: ____
Posts: 500
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Dan H will hopefully direct you to a previous thread about a year old where he described rather well the mixture sweep.

If timing is still good, and plug resistance and gap are still good then it is mostly a matter of understanding your own engine and the fuel pressure remaining in the servo, before you run the mixture lever forward after the iron is rolling.

A Slick start module properly wired on the LH mag, is as good as any electronic ignition and will boost the spark voltage as much as 300% while the starter is energized. It really helps ignite less than ideal air fuel mixtures.

Back to the fuel servo, if cables and your cockpit levers and stops are all set up correctly, when you shut down to cut off, there will be fuel pressure that holds about 20 PSI for a few hours, if all is right. Therefore, there is no need to prime, for the next 2 or 3 hours. Just hit the starter and after 1 or 2 blades open the mixture lever about 1/2 way and that residual pressure feeds the engine fuel and as the mixture gets just rich enough, it fires to life. If however your ICO lever OR servo does not quite hold pressure on shutdown, then it will quickly bleed pressure and fuel into the cylinders after shut down and leave you very flooded.

If flooded, leave the mixture cut off all the way and crank until the A/F ratio leans itself until it lights, then slowly advance the mixture to keep on running.

Just find Dans Post and it will throw a lot more light on the subject.

Also from all the reported cranking, your solenoids might be deteriorating to where your cranking RPM in not quite as fast as it used to be.

Last edited by F1R : 04-18-2017 at 07:26 PM.
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  #5  
Old 04-18-2017, 07:31 PM
JamesClarkIV JamesClarkIV is offline
 
Join Date: Feb 2011
Location: Gainesville, VA
Posts: 49
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The mixture at ICO will hold pressure. In fact, the heat soaked engine will cause the 27 PSI to increase to 50 PSI as the fuel heats after shutdown. I note two conditions when I try to restart hot. Either the fuel pressure will be >45 PSI, in which case I will crank with mixture ICO, or the pressure will be < 10 PSI, where I will try to prime just enough to restore fuel pressure. However, when I do this, I hear the fuel boiling off in the injector lines. Cranking RPM still seems strong.
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2015 RV7A
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Aircraft Blog: jamessclarkiv.com
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  #6  
Old 04-18-2017, 07:42 PM
DNeufeld DNeufeld is offline
 
Join Date: Aug 2016
Location: Coeur d Alene
Posts: 33
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If there was a timing drift, it could mean the points are wearing advancing the timing. Sounds like it stabilized so?? If the point gap changes in the mag the timing changes.

There are a few opinions on hot starting an injected engine. This works for mine.

Throttle open slightly like an 1100 rpm idle position.
Mixture at idle cut off.
Boost pump on for 3 to 4 seconds before cranking.
At the first kick mixture full rich.

Usually takes 3 to 4 blades. When I don't use the boost pump, many times I wouldn't be able to catch it going to rich. I leave the boost pump on for a minute or two after. Idles better. I tried using the flood method some say works for them and saw a wet spot on the ground about an inch in diameter where raw fuel puked out the exhaust. Washing the cylinders is not good. Might have someone watch the exhaust to see if you are flooding or excessively rich, black smoke?

Last edited by DNeufeld : 04-20-2017 at 11:22 AM.
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  #7  
Old 04-18-2017, 07:56 PM
lr172 lr172 is online now
 
Join Date: Oct 2013
Location: Schaumburg, IL
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Timing drift to higher BTDC amounts can be caused by point wear, cam wear or rubbing block wear, as well as movement of the mag in the accy case. I would expect the parts in a brand new mag to wear in a bit in it's first 50 hours and wouldn't be surprised by a 4* drift. However, I wouldn't expect to see it every 100 hours. If that's happening, you should be sure that the cam/rubbing block are well lubed and the points aren't wearing or developing pitting (usually a bad condenser).

The e gap does not directly impact the spark timing, though it is set with the points. It relates to the phasing of the magnets to the point opening. Proper egap timing ensures the greatest magnetic field / primary coil winding charge when the points open. It directly relates to spark energy and not spark timing. The egap setting is reliant upon the points, therefore it is directly tied to the contacts, cam and block that I mentioned above. If things keep drifiting, you'll eventually want to re set the egap as it will be drifting along with the timing. However, moderately reduced spark energy shouldn't have an impact on starting unless it is way out. If it has enough energy to run well after starting, it is not the cause of your hard starting.

Larry
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RV-6A / IO-320, Flying as of 8/2015
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  #8  
Old 04-18-2017, 07:59 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 6,869
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With only one impulse mag., with everything wired properly it is the only ign. active while cranking. Getting a start after activating the non impulse mag is a strong indicator that the impulse mag. performance has degraded.

This is very common because it changes so slowly we can sometimes overlook it.

The drifted timing that was corrected a couple of times previously is a strong indicator that the internal timing of the mag. has probably drifted.

When the internal timing (E gap adjustment) of a magneto is correct, the points open at the precise moment that the magnetic field induced in the coil is at its strongest... providing the highest voltage spark possible (based on the max. performance capability of the magneto). Because of wear that can occur on different parts of the points, this timing can drift so that they open at a point of less than strongest magnetic field, and it happens at a slightly different rotation angle of the crankshaft (the drift you find when you check the timing). If you re-time the mag to the engine it corrects the spark timing but not the reduction in strength. After a couple of times resetting the timing, you can have the timed perfectly but have a large degradation in the output intensity. That coupled with slightly bigger plug gaps, aged oxidized contacts in the harness, etc., and you can have a significant effect on starting performance.
I recommend you have the left mag checked (or have someone teach you how to do it yourself).
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RV-6A (aka "Junkyard Special ")
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  #9  
Old 04-18-2017, 08:00 PM
DNeufeld DNeufeld is offline
 
Join Date: Aug 2016
Location: Coeur d Alene
Posts: 33
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Right, point wear advances timing. RHFA. Points open sooner. I fix:=)

Last edited by DNeufeld : 04-18-2017 at 08:03 PM.
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  #10  
Old 04-18-2017, 11:30 PM
Bicyclops Bicyclops is offline
 
Join Date: Oct 2012
Location: LA, California
Posts: 79
Default Wear retarding timing?

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? I'm having trouble visualizing how wear opens them earlier.

I've seen people time their mags and then tighten the hold down clamps without checking the timing again afterwards. The act of tightening tends to move the mag a little. That could possibly explain the timing being more advanced than where you set it. I always adjust with the clamps pretty snug. I will put the handle of a mallet against the mag and tap the head with the heel of my hand to make the adjustments. After I check the timing, I torque the hold downs and check the timing again.

Ed Holyoke


Quote:
Originally Posted by Leadnuut View Post
Right, point wear advances timing. RHFA. Points open sooner. I fix:=)
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