Question about my fairbanks Mags

[taylorcraftbc65]

My 1940 BC65 was in storage for 2 years, and when I recently fired her up a month ago, I gave her six blades to prime her, about an eighth of an inch of throttle, one handed the prop, and she fired right up. I taxied her over to the FBO, where my sweetie Pie and I switched the Bungees, (that tool that I got from a fellow member made it SO easy, I felt like I was cheating).

After that, we installed new tires on the main gear, and pulled and packed the main gear bearings, while our friend and A&P checked our compression, and it was between 65 and 67 PSI, with the timing dead on.

The last thing that we did was change the oil, and then went to fire it up.

The engine that fired up on the first pull cold, took six or seven tries to fire up when warm, and it has never done that before. Once fired up, she ran fine, 50 RPM drop on each mag, max static was 2100 RPM.

A week ago, I went to fire her up, and did everything the same as I always have, she tried to start on the second, third and fourth tries, but she kicked BACKWARDS for two blades each time, (I still have ALL my fingers), but on the fifth shot, she fired right up perfectly. I chained her tail wheel and everything was perfect. I then went to the FBO and asked them if it was possible to have broken an impulse coupling on one of the mags, causing one of the mags to fire too soon, causing the engine to kick back.

I then asked if I found out which mag was still clicking, and then started on THAT one, switching to both when it was running. They then told me that only one mag HAD a coupling, and I should start it on the Impulse coupled mag, and then go to both. I told them that I had always started it on both mags, and never had any problems, but I'll do what it takes. WHICH mag has the impulse coupling? I think that they said it was the left, but I don't remember.


Brie

[Robert Lees]

Re: Question about my fairbanks Mags

No rules, but tradition and vintage aircraft decorum usually dictates that the left mag has the first impulse.

If no mags have impulse, you have to swing like billy-O with switches on both.

If both mags have impulse (like the new Slick types) then it doesn't matter what you do with the nag switches (as long as they're not "off"...and even then, the darn thing could still start, like all mag-fired engines).

If you're not sure, pull the prop through ....slowly....(safety stuff being observed of course) and you'll hear one impulse click or two...if only one, I bet you a penny to a pinch of Elephant dung it'll be the left that has an impulse.

If you have a broken impulse coupling, it'll sound like a bag of nails on that mag.

I'm going to edit your post to put a few paragraph spacings in...it's ever so hard reading such a solid block of text.

All the best, and long time no see.

Rob

[taylorcraftbc65]

Re: Question about my fairbanks Mags

Thanks for the English lesson by example, Rob. I actually know that stuff, I was just typing really quickly, and I let it all run together.
No bag of nails sounds when I start it, I bet that would sound like a twenty car Freight Train, with every car having a flat spot on a wheel, when running.
Brie

[Hank Jarrett]

Re: Question about my fairbanks Mags

Welcome to Hank's "everything in one paragraph" club. I get the private note every once in a while when I forget and type everything with no breaks too. ;-)

Hank

[magman]

Re: Question about my fairbanks Mags

My take is a broken Impulse Spring is the most common thing I

find with a DEAD or nearly dead mag.

A broken spring RETARDS the timing by a considerable amount ( 30 degrees?)

Slicks tend to break but the pieces seem to jam enough that the engine will at least run albeit

a 400 -500 SMOOTH drop.

It is possible the Coupling could be rusted from storage & not functional.

That would give a weak but ADVANCED spark.

That would give you kickback.

[Mark Julicher]

Re: Question about my fairbanks Mags

Look at the magnetos. The one with an impulse coupling generally has a spacer between the magneto and the engine to accommodate the extra room needed by the impulse coupling.

How old are your spark plugs?
A Bonanza owner complained that it always took a lot of cranking (10 blades or more) to start his engine.
I tested the resistance on the sparkplugs and found only two of 12 to have electrode resistance under 5K ohms and the rest of them were 100K to 5M ohms. All the plugs fired fine in a plug tester, but recent magian articles have been touting the idea that a good plug should have less than 5K ohm resistance.

We changed the plugs and this plane started on the second blade. Owner was amazed and so was I.

[taylorcraftbc65]

Re: Question about my fairbanks Mags

Well Hank, I guess it's a case of, if we upstart yanks insist on speaking English, it damn well ought to be PROPER English.

[taylorcraftbc65]

Re: Question about my fairbanks Mags

Look at the magnetos. The one with an impulse coupling generally has a spacer between the magneto and the engine to accommodate the extra room needed by the impulse coupling.

How old are your spark plugs?
A Bonanza owner complained that it always took a lot of cranking (10 blades or more) to start his engine.
I tested the resistance on the sparkplugs and found only two of 12 to have electrode resistance under 5K ohms and the rest of them were 100K to 5M ohms. All the plugs fired fine in a plug tester, but recent magian articles have been touting the idea that a good plug should have less than 5K ohm resistance.

We changed the plugs and this plane started on the second blade. Owner was amazed and so was I.

I just bought the plugs prior to firing up the engine the first time that I spoke about. They were brand new the first time that I spoke about, and as of right now, have a total of three ground run ups and a little taxi time on them probably half an hour total.

[Howard Wilson]

Re: Question about my fairbanks Mags

Hey Brie,
Did you taxi it over on the old plugs, then put the new plugs in?
If so, could be one or more bad new plugs.... had that happen to me.

[taylorcraftbc65]

Re: Question about my fairbanks Mags

No, I taxied over on the brand new plugs. The A&P thinks that the gaskets in the NAS3 dried out, and are letting a little air into the internal workings of the carb. I don't see any fuel seeping on the outside of the carb though. We just got a rebuild kit from Aircraft Spruce, and will rebuild the carb next weekend.

[Mark Julicher]

Re: Question about my fairbanks Mags


Well the spark plug idea was a loser…
How about the condition and security of your intake rubbers?

[Pearson]

Re: Question about my fairbanks Mags

Brie,

Lots of good suggestions here! Sounds like you have eliminated bad impulse couplings as the culprit. So, in my mind, the only other possibility is the timing is off. OR....... maybe, just maybe, someone accidentally got one of the plug wires on the wrong plug. I don't mean to insult anyone's intelligence, BUT, if I read correctly, you said it started fine-and then your mechanic did a compression check. And then it was hard to start. Even a pro can let one of those wires get hooked up in the wrong place. And I have seen engines run with all kinds of criss-crossed wires. Usually they will pop back through the carburetor, but not always.

[Hank Jarrett]

Re: Question about my fairbanks Mags

Mixing plug wires is NOT hard to do! I have done it MANY times on cars and caught it many times for others who couldn't understand why a minor issue (or test) caused the engine to go completely nuts. It was a MAJOR joke in the Triumph sports car community when we found that the Chilton's manuals SHOWED it wrong.

There are a few places on the internet that use less than clear diagrams for the wiring and the Continental manual shows two different layouts (at least it looks like it) for mags with the ignition leads on top and in the back for different types of mags. Interestingly, one of the old Continental manuals has photos with the plug wires WRONG in the front of the manual (I was trying to get the lead routing right).

I got so frustrated I popped a valve cover to CONFIRM that the piston was TDC with both valves closed and set the mag to fire that cylinder. Then I went around the engine with each cylinder and mag position to be SURE. Not really necessary, but after all my confusion the first time I wanted to be SURE and it helped me picture WHY the firing order was what it was. I did a visual on the number one cylinder the last time I put mags on to make SURE I was starting out right again. Engines don't run when a pair of plugs are mixed and don't run at all if the plugs are firing on TDC of the exhaust stroke

Hank

My bet is still not on plug wires, but I remember my MASSIVE confusion the first time I got them mixed up.

[woodmw]

Re: Question about my fairbanks Mags

I don't think you could have a good mag check, as per opening post, and have two plug wires crossed.

[VanDy]

Re: Question about my fairbanks Mags

I have noticed on my Eisemann's that if I only run them on the ground for a few minutes, shut down, and try to start up quickly it is a pain, seems like they got just warm enough to get some condensation in there.

Not to insult anybody but... what are the chances that it was flooded when you try to start it warm? Maybe the idle mixture was last set for the warm season?