Ryan ORL

I have the Slick start unit also, and a Skytec starter… not sure whether it turns over that fast, never considered it. Anyway, the Slick start is great for hot starts… I do wonder if it’s somehow involved, in that you can get the engine to start catching when ordinarily it wouldn’t (and therefore you can have the impulse engaged, then unengaged, then engaged again in succession if it’s a bit unstable before it finally gets going fully)

Well fortunately a few engine shops responded quickly and the prices weren’t as bad as feared. Western Skyways is going to handle the IRAN this time.

As for the color of the cracked material, I believe it probably wasn’t cracked at all until it finally destroyed itself in one violent event. The persistent failing I believe was the pawl rivets wearing and elongating their hole. And probably the pawls themselves were wearing some on the “heel” end. Some of that’s visible in the photos. Once it finally caught at running engine speed, kaboom.

Unfortunately I didn’t get a photo of that side, but it visually looked mostly ok. Engine is definitely going for IRAN at this point so maybe we will find something more…

This is the best explanation of my failure mode I have seen https://youtu.be/Pw0FOB54tV0?si=b45tvQVACVpwxqqf (b) Pawl rivet wear. The 500hr inspection involves checking the pawl rivets for wear. Excessive wear allows the heel end of the pawl to start contacting the stop pin which will eventually cause the latching end to be thrown out. Centrifugal force at normal engine speeds keeps the latching end clear of the stop pin but when this fault occurs the sudden engagement with the stop pin will destroy the coupling which may then shed broken metal into the engine accessory case. This will likely result in both magnetos being put out of action plus further damage to the engine. Such an occurrence in a single engine aircraft will leave you looking for a suitable field in a hurry.

The impulse coupling locked up at speed and tore itself apart. How this occurred exactly is still a bit of a mystery, but a cursory examination of the internals revealed that both rivets on the pawls (the hinge points I guess?) were sheared off, with one of the holes being elongated. From my reading, loosening or failure of these rivets can allow the pawls to shift outwards slightly and grab onto the catch pin when they should be held in by centripetal force. This occurring at normal engine speed results in the damage you see here. The scary thing here is, given this happened well under the 500 hour inspection interval, it is not something that can be inspected reasonably at annual or any other way without disassembly. And this can in theory fail in flight.

Savvy seems to agree in this case. There's a lot of large metal fragments missing into the engine. They were onboard with a simple repair if the pieces could be accounted for, but unfortunately not. In fact, when the magneto was removed, there was a mass of metal dust/sludge that can only be described as the consistency of toothpaste. Plus presumably lots more that went down into the accessory case. And the gears on the engine side did sustain some minor damage. In principle it needs just a look through of the accessory case and the sump flushed out, but I don't think anybody is signing their name to such a thing under the circumstances.

It's at the mx shop attached to WestJet Air Center. They are reluctant to do anything with it without an engine shop looking at it for liability reasons and honestly I don't blame them. I think the engine would have to come off anyway to open the accessory case on my J. The right mag is indeed no impulse and was already replaced with a brand new Champion Slick, and is no longer a QAA mag. Unfortunately the left mag was a QAA Slick, and the only reason I had left it that way was because, at the time (no longer), the engine was under warranty. I definitely will be going SureFly. In the meantime, I think we will be doing a brand new Champion Slick on there. I need to discuss w/ the engine shops whether they can do it with the SureFly from the start. Never had any kickback during start.

Unfortunately a rather large part of the impulse coupling itself is lost into the accessory case (and is presumably in the sump)

Pretty good view of the damage here, definitely needs replacement. Nothing much was visible on the engine side gear, just some small chipping. The biggest issue is the missing ear of the impulse coupling, which is a big chunk!

Here is an opinion from Aircraft Magneto Service, who were kind enough to offer an opinion: Impulse cams failures happen, but I would call it exceptionally rare. QAA are now exclusively using Hartzell components, they have issued at least one service bulletin (SB 225) in which they had an issue with the snap rings coming loose. I have not seen many Hartzell mags 2024 or newer, its not out of the question that they have a manufacturing defect on newer impulse cams. Engine vibrations do reek havoc on impulse cams, If you haven't I would ensure the prop is balanced and no unusual vibrations are occurring. When installing the drive gear on the magneto, the drive gear should have some "slop" to it, end play up and down. I have experienced issues on Hartzell cams before where the gear was too tight and have to polish the black oxide off the portion that fits up through the gear. Also its prudent to apply grease inside the gear to prevent binding. Snap the magneto over in your hand after the gear has been installed and ensure its "smooth", no binding. Steve Cotton AMS

I had already replaced the right magneto w/ a brand new Champion Slick for unrelated reasons (chasing mag noise, didn't solve it) I think for the impulsed mag (left) I will definitely be going SureFly to get rid of the couplings altogether.

I think when all is said and done here, there is no way I install another Slick impulse couples magneto… I will almost certainly go to a SureFly. That being said that only covers one mag… what’s involved with going to Bendix on this engine? Aren’t they larger?

Maybe I am not seeing it on their site but do they do engine work? Otherwise I’m not sure what I might be able to get their help with, we are AOG in KRAP so couldn’t get the plane itself to them in any case.

Incidentally… anyone who can recommend an engine shop somewhat near South Dakota, would love to have some other options

More of the impulse internals

tl;dr - I have had two impulse couplings destroy themselves in less than 200 flying hours, resulting in 1 and now more than likely 2 engine IRANs. Background: I had my Mooney M20J's IO-360-A3B6, equipped w/ Slick 4372 and 4370 magnetos sent for major overhaul in January 2024. It returned to service in March 2024 and had 110 trouble-free flying hours, with no adverse symptoms. In fact, we flew to Alaska and back, and everything performed perfectly. Engine ran like a top and barely used any oil and leaked not a drop for 110 hours. In July 2024, when starting up the engine at my home field self-serve pump, I heard a strange (very loud) whirring sound that I thought was an electric fuel pump sound at first (which should have been and was off, as in a normal start). The engine ran very poorly so I shut it down. After some simple investigation, we found pulling the prop through revealed the impulse coupling was very messed up. Rather than click-180-click, it was click-click-click. My home shop removed the left magneto and discovered that the impulse coupling had destructively let go, destroying the magneto drive gear, damaging the accessory drive gear(s), and rained metal debris into my accessory case, resulting in the engine being removed for IRAN and sent back to my engine shop for a warranty claim. The engine shop dutifully performed an IRAN under warranty... and apparently the magneto shop (QAA), paid for this labor, since they were the provider of the magnetos during the major overhaul. After some delays, I was back flying in October 2024 with a freshly IRAN engine and a replacement (still QAA) Slick 4372. Due to some electrical issues (unrelated to this), I have only been able fly around 80 hours since. Fast forward to this week. As I write this, I am in South Dakota and my Mooney is at KRAP. I started up the aircraft, and it ran fairly poorly. (Although without the loud whirring sound as before). A quick magneto check revealed that the left magneto was DEAD. Engine totally dies. Shut it down and inspected. On a hunch, pulled the prop around by hand. NO impulse clicks at all. Shop on field took a look and we quickly removed the magneto to find... utter carnage, again. Photos attached. It appears that the rivets failed in the impulse coupling and the pawls became stuck at high speed and the whole unit destroyed itself, breaking off large, thick metal chunks and again damaging the gears. I am at an utter loss. How could this happen again in so few flying hours. Is there anything on the engine side that could be causing this? Could a drive gear be misaligned or wrongly-sized or putting side load on the magneto drive gear or something? Looking at the accessory drive gears I see absolutely no way this should affect the impulse coupling but again I have no idea. This is getting into serious money now and nobody has any ideas what the hell might be going on here.

See everyone there!

I target 1250 with mine also. Any higher and the CHTs are unacceptable.

I have both but I keep my G3X default (and on my iPad in ForeFlight) to showing SXM always. I almost never look at the ADS-B WX in my own airplane. (But I use it often in aircraft that I instruct in) SXM weather is just better. More detail, further out, faster refresh, etc. Now, maybe that isn't worth it for the type of flying you do, but it depends. But, as a Central Florida pilot who is always contending with thunderstorms, one feature of SXM that I find absolutely crucial is the ability to look at both Composite and Base Reflectivity. ADS-B does not offer Base Reflectivity, but that is the picture that shows you better where the really nasty stuff is. I don't particularly care about precip falling up in the flight levels. Particularly after the thunderstorms have begun to dissipate, the Base vs. Composite picture can tell two very different stories. I also appreciate that SXM has the storm cell attributes, etc. It has a few nice little features like that.

Mike and GeeBee, that theory sounds very plausible to me! Will definitely report back what happens w/ the new condenser. I suspect you're right.

Going to try that and see what happens, thanks everyone!

I don't know the exact mechanism but the logic goes something like this... (Mike Busch described this calculation in general terms on a podcast once, but it basically just follows logically): First, the engine monitor has to decide whether the engine is ROP or LOP. This can probably be pretty easily approximated just from looking at whether the fuel flow is in the plausible range (given those tables) for "best power mixture". Anything less than a particular fuel flow for a given MP/RPM combo can be assumed to be LOP. If ROP - Excess fuel, air (MP) is the limiting factor. % power is given by MP/RPM table lookup. Fuel flow has little measurable impact on horsepower, probably mostly disregarded. If LOP - Excess air, fuel flow is the limiting factor. % power is computed by fuel flow and RPM only, probably using some figures from the BSFC curve.

So this is a bit of a strange problem. Starting a few months ago, I started noticing significantly diminished comms reception, and a loud rapid clicking on the comms. Some brief debugging revealed that it wasn't really comms reception at all, but rather the loud clicking noise was playing hell with the GTN auto-squelch and the problem seemed to be slowly getting worse. Some further troubleshooting revealed that the problem was only evident on the RIGHT magneto, i.e. the clicking noise disappeared entirely when running only on the LEFT magneto, and the clicking was certainly RPM dependent. It was easy enough to break squelch on COM1 and just listen to the click disappear and reappear when switching the mags. My local shop started debugging this, first checking for loose grounds (etc) and checking the magneto harness for pinching, chafing, or arcing. They found one slightly loose shield and corrected that. They did some kind of high voltage test on the harness (~110 hours old, new at my recent engine overhaul) and found no problems. There was also nothing visually obviously wrong with the harness or leads. So I did a bit of further debugging with a portable radio. The clicking was actually audible on the portable comm radio with all my aircraft electrical systems entirely turned off, in other words it was most definitely arcing somewhere, and our assumption was it was inside the magneto. Sure enough, the shop tested the condenser and found it was a bit out of spec, and they put in a known-good spare that they had while we ordered a new one and waited for delivery. That cured the clicking entirely. Comms totally quiet on either mag. Hooray! As an engineer myself I also wanted to understand what went wrong... so fortunately this also entirely made sense... a bad condenser would lead to the points arcing, case closed, I thought. The new condenser is due to arrive this week, so I am still flying on the 'spare' one. I had around 5-6 trouble-free flying hours on it. But on Saturday when I went to fly the airplane... the clicking was back! Now, we haven't had a chance to dig into this yet... we're of course going to install the new condenser, but my concern is that either I am just enormously unlucky, or something else is killing the condenser and the new one will just fail again. So does anyone have any theories on what the hell might be going on inside this magneto? The mag itself is relatively recent... 110 hours also, from the overhaul, it was an overhaul unit from Quality Aircraft Accessories. At this point I suspect there must be some other internal fault there... I am inclined to just send the whole thing out for overhaul or even try to get an exchange unit. I am honestly tired of chasing the issue. Could it also be something with my plugs on that side? I run all Tempest Fine Wires that have maybe a few hundred hours on them.

Certified Engines Unlimited in South Florida. $1500 expedite fee. To be fair they only promise 8 weeks for that but they got it done in 4.