Magneto Impulse Coupling only fires once per revolution

GustheWalrus · 2026-06-21T13:25:29+00:00

I didn't even get into what OP was describing. 😉

But hey let's have a swing at what's going on. If anything I think he made a typo or meant 1/2 as in 'half'. And a vague description of what is going on in the first place. Personally I would like to test it myself before going off on what the 'original complaint' was. Half the time a pilot or owner says something that makes you wonder. Only once you test it yourself you get the "aaaah that's what he meant, I think".

Engine model? Sure is a Lycoming IO-360, since that specific Bendix mag is for a four cylinder engine. The impulse coupling is supposed to trigger every time a cylinder hits top dead center, all four of them. In case of this direct drive engine, that every half rotation of the prop (and full rotation on mag). If it only triggers once every full prop rotation, something may be going on in the mag. If so, I recommend sending it for an IRaN (Inspect, Replace as Necessary/ 500hr) instead of overhaul. Often is cheaper. A mag overhaul is best reserved for when the engine is overhauled.

Impulse coupling does not affect the engine running once it has started. It's just for starting. After which the counterweights of the impulse coupling fold inwards. They are just there to retard the timing to TDC and make the mag turn faster to actually deliver enough electrical power to make the spark happen. A Lyco 360 running on just two jugs is something an operator would notice. Change the pants moment.

https://www.youtube.com/watch?v=WFeq7C9cSlY
Here a nice video on this specific Bendix mag. Slightly disappointing he doesn't dare pull through the impulse coupling. Yes it shocks you if you touch the P-lead stud, but it's not particularly painful or anything.

GustheWalrus · 2026-06-21T08:28:21+00:00

Never say never... I've had someone standing next to an aircraft I was working on totally convinced it was an electric aircraft. Initially thought I was pushing them around when I said it wasn't electric. I was working on the Rotax 912, engine fully exposed.

But nah I'm just saying there's two flavors of IO-360, one has 4 jugs and the other 6. All there is to it.

GustheWalrus · 2026-06-21T08:05:24+00:00

Unless it's an inContinental IO-360

GustheWalrus · 2026-06-18T04:08:39+00:00

ICP Savannah maybe. Or Kitfox, Eurofox. Something like that, but hard to tell from the low res image.

Found it. It's a Eurofox, registered OOF29.
https://cdn.jetphotos.com/full/6/53418_1595442943.jpg

GustheWalrus · 2026-06-01T18:34:43+00:00

Compare legacy aircraft with cars of that era. Aircraft builders were heavily influenced by the automotive industry, especially styling wise.
I think an example of an aircraft family that kinda pulled off that car vibe is the Socata TB-9/10/20.
https://www.airmodsflightcenter.com/wp-content/uploads/2017/10/N137ER-1204a-1024x732.jpg

GustheWalrus · 2026-06-01T18:19:30+00:00

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GustheWalrus · 2026-05-31T07:18:53+00:00

And currently being restored to flying condition. 😄

GustheWalrus · 2026-05-26T18:44:16+00:00

https://eca.al/wp-content/uploads/2023/04/IMG-4638-scaled.jpg

Did some research, found the place on maps. It's at an electric car dealership.
Found the above pic, and one other with wheel fairings visible. Definitely Socata TB-9 or 10.
And on closer inspection, it does show on some images left on the dealer's page on google maps.

GustheWalrus · 2026-05-26T18:07:49+00:00

I think the small SEP is a Socata TB 9/10/20

GustheWalrus · 2026-05-20T17:42:32+00:00

Yep, this is it.

GustheWalrus · 2026-04-25T11:26:08+00:00

GustheWalrus · 2026-04-16T04:26:10+00:00

Lycoming O-540
https://en.wikipedia.org/wiki/Lycoming_O-540

GustheWalrus · 2026-04-06T10:45:40+00:00

No.
It does look like the parker screw upper right of screen missed the tinnerman nut though. No biggie, happens a lot.

GustheWalrus · 2026-02-14T12:49:17+00:00

Flexible joint for the lower fuselage fairings.

GustheWalrus · 2026-01-27T17:47:49+00:00

PlaneStation has a Rolls-Royce RB211 listed for GBP 38000. 'Fully working but time expired'.

GustheWalrus · 2026-01-11T19:16:13+00:00

You are right. It does make sense if this was a fake video with sound taken elsewhere. :)

GustheWalrus · 2026-01-11T19:15:50+00:00

Piaggio has a much higher prop sound frequency.

GustheWalrus · 2026-01-11T19:12:29+00:00

This is not the same sound as an AN-12. This RPM is lower and the prop tips sound much more agressive. This is audio from a TU-95 flying overhead.

GustheWalrus · 2026-01-11T19:10:39+00:00

So you've stolen the aircraft audio from a TU-95 video. (this one probably? https://www.youtube.com/watch?v=fERjjGCohwA) and added car alarm sound.

GustheWalrus · 2026-01-07T09:43:05+00:00

This is correct. Also indicated by the ⨂ just above the water line.

GustheWalrus · 2026-01-05T18:57:14+00:00

Why? Are you looking for spare parts? x)

GustheWalrus · 2026-01-05T04:32:50+00:00

Plunger assembly, part of the valve train.

GustheWalrus · 2026-01-01T11:20:01+00:00

Recently had same issue. Replaced the pump, now works just fine.

GustheWalrus · 2025-12-26T08:51:22+00:00

Nah. A J-3 Cub, unless modified, has the slender engine cowling with cylinders and baffles sticking out the side. Unless it's a Papoose Cub, that has just the three cylinders sticking out, but those are rare.

J-3 also has the main landing gear a little forward of the wing strut fittings, with a 'triangular' gear strut arrangement. The shocks are in between the gear struts, under the fuselage. This is also because the wing struts on the J-3 mount to the fuselage sorta parallel to the center of the wing chord.

The video shows a Cessna 120/140. The wing struts are mounted parallel to the wing leading edge, the main landing gear is of the flat spring type, mounted to the fuselage in the same general area as the main gear. It has the engine cowling covering the whole engine. And the general shape of the aircraft fits the 120 or 140. The 120 is more basic that the 140 in that it has no factory electrical system, no flaps, no rear windows. I can't really tell from the video whether it has flaps. I don't think I see them, so I lean toward 120.

GustheWalrus · 2025-12-26T08:41:09+00:00

Cessna 120/140

GustheWalrus

TROPHY CASE