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Magneto Timing Drift & Hard Hot Starts

JamesClarkIV

Active Member
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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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.
 
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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.
 
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?
 
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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
 
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).
 
Right, point wear advances timing. RHFA. Points open sooner. I fix:=)
 
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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


Right, point wear advances timing. RHFA. Points open sooner. I fix:=)
 
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.
 
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/1821072/53cb5d34-0cd6-4d98-928d-68b6812d2a16
My first attempt at doing this test.
 
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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 :rolleyes: 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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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.
 
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
 
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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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.
 
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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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.
 
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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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?

No doubt it will help. I generally clean my bottom plugs ever time the cowl is off every 35 Hours for an oil change. I use a dental pick only as bead blasting wears the electrodes and insulators.

On the ground, you can lean to max RPM and that is more than 1/2 way to cut off on mine. Taxing around below 1000 RPM is no issue.

With good technique and good understanding of the fuel condition starting is no big deal. However, addition of a Slick start will save cranking and light off fat or lean mixtures with ease.

With a slick start, it will start like a Toyota hot or cold, (if plugs and mags are good.)
It will save the cost of a battery and starter and a lot of headaches.
 
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I'm looking for help understanding my hot starting problem....

....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'm quite interested in getting a single EI to replace a mag as I think this may help my starting (#1 goal)...

I believe your troubles are primarily mixture. I'm very confident that if you perform the clear engine procedure on every hot start you will be much better off, regardless of ignition. As a data point, my Rocket started fine with no impulse, and no Slick start - just regular old mags.

However, to your question about EI - yes, it will help your starting process. It would be a tough sell to justify it as a starting aid only, but that's for you to decide. If you are buying it as a starting aid only and have no interest in chasing down LOP optimization, then I'd look hard at an ignition that can be programmed to have a flat (or zero) advance curve. In other words, one that provides a strong spark at start, a healthy retard function for no kickback, and the ability to otherwise emulate the magneto timing that you are comfortable with. If you decide to go this way, take a good look at CPI, as it can do that as well as being optimized for cruise should your mission call for that in the future.
 
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My guess is that the majority of the hot start issue is fuel injection related.

Wouldn't hurt nor cost all that much to have a knowledgeable mechanic go through your mags. With that little time, there shouldn't be many parts needing replacement. I had a mechanic work on a mag once and didn't fully tighten the points adjustment screw.....my engine suddenly started missing and running alike a 3 legged dog on final.... My point here is that gross miss timing internally can cause significant issues. By the way, my experience has been a slight timing advance when breaking in new mags. Maybe a degree or so. I believe the "book tolerance" is +/- 2 degrees? If that is so, then it could have came from the factory set at +2 and you had a little wear afterwards. No way to really know without having the Mags IRAN. Just don't get frustrated if all the mag work doesn't completely solve the hot start.
 
Mine did exactly the same as you describe. Left impulse mag was outside the recall range of serial numbers too, but still had the internal wear, or so I believe. It was only just outside the range by the way. Pulled mag off and apart and all items tested ok. I had details from my LAME in Australia. Replaced the mag as that was the most recommended idea on Vans and the internet I could find after several months searching. Also replaced all 8 champion plugs with Tempest. Plugs had a wide range of resistances with some well over 5000 ohms. I used to worry about hot starts away from home base, but now no longer do. In fact I think a true hot start, say after landing, refuelling and then taking off sees a better start than when cold. Start procedure is master on, flaps up, mixture cracked up to 1/4 in, key to start and add mixture til it fires. Works every time now. For me, the cost of replacing the mag has given me a massive peace of mind I never had before. This was after 18 months of going to flyins and having all sorts of help from other M1B owners, tech councillors etc. Other owners could never understand my problems as theirs started using the procedure I described.

Good luck with getting a resolution. Perhaps if you could "borrow" a left impulse mag you might solve your problem. An impulse mag was way cheaper than the equivalent EI mag for my purpose.
 
In the beginning, I had difficulty getting consistent quick engine start hot or cold.

But over time learned the key is proper amount of fuel available, not too little, not too much. The envelope is not large.

Today the engine starts cold on first or second blade all the time using impulse mag only. (I stopped using EI for start because if rpm dropped off immediately after start, it would kick back.)

On hot start it is more difficult because you don't know just how hot it is. But same applies, if correct amount of fuel is available it will start right off. It is very easy to flood when hot.

I do not suggest a technique regarding prime and having just the right amount of fuel available. It depends on Fi system and internal temp of engine. It is a matter of discovery with each engine. If one method does not produce desired result, adjust it. The engine will pop right off if it is primed just right.

I say all this believing the problem is fuel related, not ignition.

I have mag connected to top plugs, that helps.
 
My IO-320 engine started like a champ cold or hot until about a month ago. Then, when trying to start cold or hot, it was difficult or would not start. Magneto had 300 hours since new. Short story is; took the left magneto (one with impulse coupling for starting) to a reputable shop in Tulsa for a check up. On the test bench, the magneto fired ok when it was cold, however after heat soaking it, the coil started failing. It was overhauled while I waited. Starting problem now resolved.
David, Steve, and John at Quality Aircraft Services in Tulsa provided excellent diagnosis and customer service on this problem.
 
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