Kickback During Hot Start

So this has happened to me twice now, and I don't know if it is standard Lycoming behavior, or if I should be troubleshooting my airplane.

I have a O-360-A1A with aftermarket Fuel Injection (Airflow Performance) and a purge valve. I've got dual P-MAG 114's with Auto Spark Plugs. The airplane starts cold like a dream with MAYBE 2 seconds of prime.

When the engine is hot, I'll use the purge valve to cycle cool fuel into the spider and the engine starts with no problems.

A couple times now though, I've underestimated how warm the engine is, and have attempted my cold start with 2 seconds of prime when the engine has flown within an hour and is warm. Twice now, the engine has fired, and the prop has rotated backwards (counter-clockwise from the cockpit). The first time was accompanied with a little smoke and burned Avgas smell, the second time (a few weeks later) was much less exciting.

Now, obviously this isn't good for the engine. My first thought was that something was wrong with the timing of the P-MAG's. I have mine indexed 2 degrees after TDC, and the P-MAG should retard another 4 during start, so 6 degrees after TDC should be well past the point of kicking the motor around the wrong way. I took the cowl off today and checked the timing, both green lights came on at the same time at 2 degrees past TDC.

My other thought is the excess fuel is simply being ignited by the wasted spark during the exhaust stroke? The answer here is less prime.

Any other ideas or things I should check? The engine runs smooth in flight, with CHT's in the 300's now (50 degrees outside) and 350's during the summer months. Oil temperature is right around 190 degrees, and EGT's have a fair spread, but typically peak around 1400-1450. When leaning. The engine runs smooth. Mag check drops ~150rpm at 1,600rpm during runup, but runs really smooth.

Is this normal behavior if one overprimes a fuel injected engine during a hot start? I just want to understand what's happening, and also avoid this in the future so I don't have to replace a ring gear or starter.

Same problem

I had a similar problem and the second time it broke my starter. I too had timing at one notch or 2.4 degrees ATDC with my Pmag. I went another notch ATDC which equals 4.83 degrees and problem went away. A side benefit is that CHT went down some and there's less advance where you don't need it based on recent comments from those who know more about the ideal timing advance map for Lycoming. One negative is less hp but I'm ok with the tradoff.

I have an IO360-M1B with a WW prop and PMags. I had several kickbacks that broke several teeth on the ring gear. I retarded the timing which did no good. I now have the latest software and still had an ocassional kickback. I began "indexing" the prop so that it is not immediatly up against a hard compression stroke which allows the prop to get some momentum. I have not had a problem in 75 hrs since doing this. Also remember that if it doesn't start you have to shut the mags off then back on to set the retard function for the next start.

more info please

johnfurey said:

I have an IO360-M1B with a WW prop and PMags. I had several kickbacks that broke several teeth on the ring gear. I retarded the timing which did no good. I now have the latest software and still had an ocassional kickback. I began "indexing" the prop so that it is not immediatly up against a hard compression stroke which allows the prop to get some momentum. I have not had a problem in 75 hrs since doing this. Also remember that if it doesn't start you have to shut the mags off then back on to set the retard function for the next start.

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John, Would you explain the clocking a little bit.
I am about to install a new WW 74HRT on a 0-360 w dual Pmags with latest software, and timed per their standard set up using TDC.
Catch is, we have a James cowl (extented) with a 2.25 Saber extension, so obviously the extension is bolted into the engine flange holes and the prop will have to clocked a little up or down from the called out 10/4 position.
Can I assume from your kickback issues I would want to go more like 11/5 to allow the prop to get some momentum? or am I wrong?
BTW now have Hartzell with the Pmags and no issues.

I'm having a hard time envisioning how clocking a propeller can increase or reduce a "running start" against the compression stroke unless you are hand propping the engine. In this context, the MMOI of the prop/ring gear/crankshaft is the same regardless of clocking... As far as the starter is concerned, the prop only adds inertia to the ring gear carrier.

I'm also wondering about the increasing reports of Pmags with kickback events... the latest software AND further retading the timing makes this a theoretical impossibility. Is there some other event like low voltage or EMI that is interrupting the timing? Regardless of the ignition type or manufacturer, an ignition event that occurs AFTER TDC simply can't cause a kickback in a piston engine.

johnfurey said:

I have an IO360-M1B with a WW prop and PMags. I had several kickbacks that broke several teeth on the ring gear. I retarded the timing which did no good. I now have the latest software and still had an ocassional kickback. I began "indexing" the prop so that it is not immediatly up against a hard compression stroke which allows the prop to get some momentum. I have not had a problem in 75 hrs since doing this. Also remember that if it doesn't start you have to shut the mags off then back on to set the retard function for the next start.

Click to expand...

I think your referring to the Run Mode Start Delay (RMSD) which is disabled on my P-MAG’s as I don’t have a composite oil sump as referred to in the manual. I believe the spark advances every time the key goes to start.

This still doesn’t explain how a spark event occurring 6 degrees after TC (4 degree delay + 2 degree indexing) is causing kickback? I wonder if the P-MAG isn’t firing exactly when it says it is...which is concerning.

RhinoDrvr said:

I wasn?t aware of this....that would explain my problem. I?ve got a Hartzell constant speed prop, so it should have some flywheel effect.

Is the requirement to shut the mags off after an unsuccessful start attempt documented anywhere? I would think it should retard any time the key goes to ?start??

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In the "old days" this was true. I've been flying Pmags for 13 years and have kind of trained myself to shutdown and reboot after the (admitedly rare) failed start. I understand the new software "fixes" this issue. No need to reboot after a failed start.

Toobuilder said:

Regardless of the ignition type or manufacturer, an ignition event that occurs AFTER TDC simply can't cause a kickback in a piston engine.

Click to expand...

I would also add that this should be true regardless of prop type, although emag will tell you the concern is more for lightweight props like a whirlwind. I don?t follow their logic - why would that matter if the ignition is firing after TDC?

I have added a 1-2 degree correction factor to my timing, which has greatly reduced my kickbacks and backward running prop incidents but it still happens every once in awhile, usually on a 2nd start, so battery voltage and spinning speed are factors here. If I need a 2nd start attempt, i now keep the ignitions turned off until a few seconds after hitting the start button to let the prop get up to maximum spinning speed. I can?t recall ever having a kickback event when doing that.

Erich

I agree that if the spark isn?t until after TDC there should not be a true kickback but the symptoms and result are very similar. Depending where the prop stops on shutdown if I try to rotate the prop forward it may travel freely to the start of the next compression stroke or it may be up against a hard compression requiring significant effort to rotate so now I always advance it through the upcoming compression and rotate it back to the beginning of the next stroke leaving it in ?dead zone? of maybe 60 degrees before the starter meets much resistance. Might be coincidence but no problems since doing this.

Is this potentially the wasted spark igniting the over rich mixture in the cylinder kicking the prop backwards?

Since you have your P-mags upgraded to V40, my first question is how did you index your prop?

With version 40, you P-mags should fire at 4.2 degrees past TDC, then add to it the amount you have "clocked" your prop, you should be well past the point of being at risk for kickback.

Are you moving the prop to TDC in the direction of the prop rotation without backing it up? If you go past TDC, back way up and slowly bring the prop back to TDC.

What mark are you using to set TDC, the engine case split and back of the spinner or the pin on the starter? (I have found using the starter to be more accurate.)

As for the RMSD (Run Mode Start Delay), I do not recommend using any setting other than zero.

The reason is that a few of our EICommander customers have set it to values other than zero (0) and the results concerned them. What happens I the engine will turn over a few times, pumping raw fuel into the exhaust stack. Then on the next firing event, the plugs fire, lighting off the fuel in the exhaust with a "bang" or two.

I used the pin on the starter and the TC1 mark on the front of the ring gear.

I rotated the engine in direction of rotation to TC, then bumped it a few times gradually (again in direction of rotation) until the mark was 1 gear tooth past TC and timed the PMAG there.

A lot of -4 s and -8 s have the starter button on the stick. Unless the mag and or p mag switches are located within fingertip distance of the throttle it makes it difficult to impossible to get the iron rolling at a good speed before lighting the fire.

A lot of 4's and rockets in the past have all the switches, including the mags on a RH side console. Including mine. I have been inclined to mount a pair of toggle switches just ahead of the throttle and re wire the p leads for some time.
This thread might get it on my do list over the winter.

Are you starting with both pMags on?

Carl

2 slick mags. I start on the LH side -currently a 6393 with a Slick Start booster and like to bring the RH side online as soon as the RPM starts to build. This is normally a second or two after releasing the starter button on the stick. With the mag switches located way off on the far right of the cockpit there is no way to roll the engine over to a higher cranking speed before turning on the starting mag. Regardless of magneto, or P mag with the switches in close proximity to the throttle, you can hold the starter button on the stick with the right hand, then after the RPM is at it's peak a second or two later the ignition of the starting mag can be energized. See Post #8.

I might put a second 6393 on the RH side and another SS. That way I could turn both on at the same time for even more positive ignition.

Ok, reading the OP again I have to ask if the "backwards" running happens DURING the starter opperation, or AFTER the starter is dropped? Sometimes a very fat mixture will do funny things after the starter is dropped, including some backwards rotation.

Is this a true "kickback" event? I.E, is the kickback happening while the starter is grinding away?

Toobuilder said:

Ok, reading the OP again I have to ask if the "backwards" running happens DURING the starter opperation, or AFTER the starter is dropped? Sometimes a very fat mixture will do funny things after the starter is dropped, including some backwards rotation.

Is this a true "kickback" event? I.E, is the kickback happening while the starter is grinding away?

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The kick back is sometimes immediately after releasing the starter and sometime during cranking.

Turns out, I can start this PMAG setup with NO prime from cold. I started the airplane from cold after a week of sitting in 40 degree weather with the mixture rich and no prime. Which means my 2 seconds of prime with a hot motor must have been flooding it to death. Combine this with the wasted spark, and my issue became clear.

Solution; stop using the boost pump on start.

RhinoDrvr said:

The kick back is sometimes immediately after releasing the starter and sometime during cranking.

Turns out, I can start this PMAG setup with NO prime from cold. I started the airplane from cold after a week of sitting in 40 degree weather with the mixture rich and no prime. Which means my 2 seconds of prime with a hot motor must have been flooding it to death. Combine this with the wasted spark, and my issue became clear.

Solution; stop using the boost pump on start.

Click to expand...

Piston position when the waste spark is delivered is the same as the opposing piston at ignition spark....in this case assumed to be at TDC or after.