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Magneto Mystery Solved.

7 hours.

So remember when I was trying to debug a nasty popping, backfiring, horrible magneto?  Yeah, like it was yesterday.   Matter of fact, it was yesterday.  And today.  Every engine test since first start has been a mess and the reasons are plentiful, going back to when David and I first tried to get it running a while ago. This has been going on for 3 weekends now.

First, I modified Bob Nuckolls’s electrical system diagram to include a pushbutton starter switch in addition to the spring-loaded (ON/OFF/(MOMENTARY ON) switch.  Turns out you can’t have both.  What wound up happening here is that when the spring-loaded switch was set back to center ON, it was grounding out the one magneto capable of running the engine.  I’ll get to that in a second.  In addition to that, we were never sure which wire went to which magneto, because those two bits of shielded cable never got labeled.   Lesson #1.  We did eventually test that and got the wires running to the correct mags.  We think.

If I wanted to keep my stick pushbutton start, the  On/OFF/On switches would have to go and be replaced with dual-pole ON/ON switches, which would allow me to disengage the start circuit as well as ground the mags, making them cold and safe.   I replaced those switches, and maybe here, maybe the step before, the wires got switched again and left went to right and right went to left.  The good news is that with these switches installed, the engine fired up.  Ran a little rough, but it was a damn sight better than last week.   OK, shut down right mag for RPM drop.  No drop.  Shut down left mag for RPM drop.  Bang, boom, sput, cough.

As you might expect, shutting down the “left” mag caused the engine to pop and misfire, so it was assumed that something was wrong with the right magneto.  First thing we did was switch it out for a good one, the one my hangar mate had in a plastic bag for eventual installation on his RV9.  Timed it to the engine, buzzboxed it, fired the engine up.  Same thing.   At this point it was a head-scratcher, because here we’ve just put a brand new Slick 4300 series magneto on the right side of the engine and we’re still getting popping, misfiring, the same thing.

Oh, one important detail I’ve left out of this story so far:  I don’t know how many times we pulled the magnetos and checked and rechecked the engine timing.  During this process somwhere, I the timing pin (an allen wrench or a pop rivet)  in the distributor block when we pulled the engine through to set up the engine timing.  Maybe I even did it at home before moving to the airport.  At one point, I pulled a very bent allen wrench out of the left mag and a bent pop rivet out of the right one.

I assumed that because the “left” magneto was working fine, it was the right one that was messed up, but that couldn’t be because I’ve just replaced it with a brand stinking new one.   Matter of fact, when I opened up the mag I’d pulled out of the airplane, everything looked fine.  The distributor gears were OK, the rotor was fine, and the distributor block wasn’t cracked or anything.   I left Ron’s spare mag on there  because I had more debugging to do and I didn’t want to change back to the original mag, which may have been compromised in some way, even though none was evident.

Yesterday, I thought, hm, maybe the wire going to the magneto is shorted somewhere.   So I disconnected the terminals from the mag (and took the harness cap off to be safe) and tested them for continuity.   With the switch set to “ON” there should have been no beep from my multimeter.   I got a beep.   AHA!   There’s a short in the shielded P-Lead wire!  So what do i do then? Cut the ends off the wire to the “right” mag at the switch, thinking maybe the connection shorts intermittently because I cut the insulation of the wire and the shield’s touching it.   Still beeped.   OK, that wasn’t it.. Maybe it’s at the mag end.   Cut that off.   Strip back some cable so I can test the ends.   Still beeped.   At that point the day was pretty much over.

Last night I was falling asleep reading Book 7 of Stephen King’s Dark Tower cycle and it hit me.  What if the wires were on the wrong switches?  Left is right, right is left.  That would mean three things:  One, the “short” in the P-lead cable isn’t a short at all.   The other switch was cold, so the multimeter would have beeped no matter what, because disconnecting from the switch and still connected to the other mag, there’s enough continuity for a beep.   At the mag end, testing the wires would produce a beep because they’re going to a switch in the cold/safe position.   Two, this would also mean that I’ve been debugging the wrong magneto for the last two weekends in a row.  All my attention was focused on the wrong part of the system and it didn’t occur to me to check something as simple as wiring because I’d already gone down that rabbit hole and figured I’d verified it multiple times.   Three, I’m an idiot.  Once for leaving the timing pin in the left magneto, twice for not checking the wiring, and three times for assuming things were correct in places where they weren’t.

I hadn’t planned to go to the airport today, but I did.  I figured it would only take me a couple of hours to sort this out, so I loaded up the bike and headed to OXR.   First thing I did was pull the right magneto and check the internal parts for damage.   This was onerous.  I routed my hoses and cables so they trap the magneto in a cage with no hole big enough to let it exit.   I had to take the oil pressure sensor hose off to extract the magneto.  It always makes me nervous doing that.   All I need is for a lock washer to fall down inside the engine accessory case and I’m totally screwed.   I did manage to extract it, and got it up on the bench, where I was able to remove the back cover and the distributor block.   Guess what I found:

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That right there is the rotor gear.  This spins on the shaft that opens and closes the points, making the spark.  Notice that there are two teeth missing, and several of the others are damaged.   The bottom line here is that no matter how carefully the engine timing is done, there is no way in hell this gear will drive the distributor gear in any way that will provide a spark at the right time.  To prove this out, I reassembled and installed the old right mag on the left side of the engine.   I have two impulse-coupled mags, I can do this.   I remembered to take the timing pin out, say thankya and may it do ya fine (Dark Tower, remember?).   Then, miracle of miracles happened.   The buzzbox timing process, which I am now intimately familiar with, went just like all the documentation, descriptions, and YouTube videos said it would.  Snap the impulse couplers, back off enough to get rid of gear lash, then move the prop forward to 20 degrees BTDC.  twist one mag until the light just goes on or off, depending on what it’s doing when you turn the box on.   Back the prop off again, then move it back to 20.  The light should go on right there.   Twist the other mag until the same thing happens.   The trick is to get both lights to come on at the same exact time.

With two teeth missing off the rotor gear that wasn’t ever going to happen either, so wiggling the mag back and forth on the dead spot betwene those teeth isn’t going to do squat.

But joy of joys, sing hosannah to the heavens, with two properly timed and synchronized magnetos, that engine runs smooth and strong, like a big cat purring.   Ron helped me push the ship out into the sun and I fired it up.  Rock solid, dead on.  RPM drop on both mags, just like that beat-up Cherokee I learned on.

Now I get to go back in and clean up the mess I made testing everything.  Re-wrap my wires, safety-wire the governor, everything back int its place.

More Magneto woes.

6 hours.

At this point, I’m out of ideas. I unshipped the right mag and took the rear cover off to inspect the rotor housing and gears. Even though I left a pop rivet in the timing hole and turned the prop, the distributor gear seems fine. I followed the procedure in the repair manual, and timed the distributor gear using the marks on the rotor and the gear itself, then reassembled everything and put it back on the engine. Same result, no joy on right mag. So, bad magneto, right?

Wrong. This is where it gets truly odd. Ron loaned me the new impulse coupled mag he has for his project. I timed it with the pin, put the engine at 25 BTDC and put it on. Timed it with the buzz box, and tried firing it up. Exact same result.

I now have no idea what is going on.

It’ll have to wait two weeks until I get back from training with Mike Seager in Oregon, which is in two days.

[Untitled]

5 hours.

Today was about putting things back together and getting a handle on some of the chaos.   The first bit of good news is that the oil temperature probe works fine.  I pulled it out of the engine and hit it with a heat gun and sure enough, it gave me a reading.  So I’m not going to worry about that anymore.   I secured the wires back in their bundle and i’m calling that squawk done.

I also wasn’t real happy about the weird way I had the fuel pressure sensor set up.  The Adel clamp holding it was maybe a size bigger than it should have been, and this way seems more secure:

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As I mentioned last time, I flipped the governor arm over and it seems to work just fine:

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My biggest problem with doing it this way was where the injector line was going to go.   A piece of angle solved that.   Now it’s out of the way, and less likely to be heat-soaked down near the cylinder.  I still haven’t safety-wired the screws yet, or put the cotter pin in the cable attach nut, But I think this is how it’ll stay.

Last week, Owen recommended tightening up the tailwheel chains.   Van’s recommends a half an inch of slack, but if you ask ten different people how they like their tailwheel chains, and you’ll get at least five different answers. But my chains had an inch of slack, and if I took a link out, I’d have none.  But I did take a link out of each side, and while there isn’t really any dangling slack, I can move the chains up and down by about a half an inch, and I’ll tell you, based on today’s test, it taxis just fine:

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That little gap in the rudder fairing is kind of annoying.   Not exactly sure what to do there, except put nutplates in there and hope for the best.

Today’s test was all about seeing how things went with the cowl on.  First, I wanted to make sure I could actually get the cowl on with the flipped-over governor bracket making the cable rise a bit more than it did before.   Turns out, I’ve got about 1/8″ of clearance between the cable and the top cowl, which is good enough.   And from what I remember, the cowl inflates a little in flight, so that 1/8″ becomes a little more.   And that’s fine.   I just don’t want to have to put a clearance wart in the cowl to accommodate the cable.

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But before taking it out for another test, this adjustment had to be made to the baffle material on the lower cowl.  I had to cut it back a bit, because it was covering up about 6 square inches of air intake.   Bad.   So with this mod in place, I put the top cowl on, and pinned it down.   Then I put a few of the floor panels in, and you’d be surprised how much the plane stiffens up with the reinforcing action of the panels.   I ran it up, then shut down the left mag.  Engine died.   Started it again, repeated.   OK, right mag dead.   Grr.   Still runs fine on one though.

So I said screw it, let’s taxi it around.  The new tailwheel chain tension was much better.  Now it’s more like Mickey’s Citabria, and the ground handling is nice!  I took it to the end of the hangar row, turned right, went down the next row, turned right again, then went back to the barn.  CHT’s never got above 210.   As soon as I get this mag situation sorted out, it’s time for ground runs.

\Last time, shutting off the left Mag made a lot of popping and missing, which I attributed to timing.   This time, I’m pretty sure the timing’s right, but now shutting off the right mag shuts off the engine.  Now, it might have something to do with the fact that I left the pop-rivet I was using for a timing pin in the hole when I pulled the prop through, but I can’t say for sure.   What I do know is that before, on the right mag, I had backfiring.   Now I’ve got squat.

 

Magnetos timed (again) and RPM sensor fixed.

6 hours.

One of the day’s tasks was to replace the magneto gasket we tore with a new one.   This necessitated removing the right magneto, the one that was cranky about timing.   This is also the mag that has the hinky contact spring on one of the harness wires.  I figured what the hell, I’ll make sure both are timed, so I’ll pull both, put new gaskets on both, and set the timing again.   Big mistake.   Timing mags with two people sucks, as you might have gathered from an earlier post.   Doing it on your own sucks too, and then some.   Yesterday it was hot and windy at OXR, so the hangar was warm and the doors were rattling and making freakish noises every couple of minutes.

There are various sources of knowledge as to how to time mags, but the general idea is that you turn the engine over until the crankshaft is at 25 degrees before top dead center.   Then you zero the mag position by sticking a pin in the timing hole in the back of the magneto where it will sink into another timing hole on the gear inside, thus locking the thing into the position where the points are open.  Then you stick the mags back on your timed engine.

A number of factors are at work here.   There’s the impulse couplers, there’s the slop in the mags even with the timing pin inserted, there’s gear lash in the engine itself, and there’s the ambiguity of where 25 degrees BTDC actually is.   Near as I could figure out, there’s a little lump in the rotation of the mag gearshaft where the points open.   This is no great mystery.   A cam inside opens and closes the points to make a spark.  That fires the spark plugs.  This is no different from your common Briggs and Stratton-powered suburban lawnmower.

But the magnetos are buried amongst wiring, hoses, and engine mount tubes, and getting them back on can be extremely frustrating.  The mag gasket is a little wider than the magneto housing, so it’s really easy to dislodge it.   The engine gears of the mags are also wet with engine oil, so they’re slippery.   It’s also of primary, critical importance that nothing falls down the open mag hole into the accessory case.   If that happens, game over.  If that happens, you better hope whatever fell, like a nut or a washer, falls all the way through into the oil sump where it gets stuck to a magnetic plug — if you have one.  The obstacles in the way make it easier, but not by much, to insert the timing pin into the housing with the mags more or less in place, but supporting them, spinning the gear, and inserting the pin is one of the more frustrating solo tasks there are.  The trick is to get both mags installed so they’re within just a few degrees of each other, because there’s only about 70 degrees of twist available to bring them into line.    If they’re too far off, they’ll never sync up.

The next part is relatively easy, assuming the first part goes OK.   This is where the buzz box comes in. This thing has two lights on it, and you connect the leads to the P-lead connections on the mags.  When the points are closed, the lights are on.  When the points are open, the lights are off.   Or vice versa.   Can’t remember.   The point is, the status of those lights is supposed to change when the engine turns through the specified timing mark on the flywheel.   Both mags are supposed to change at the same time.    There’s actually enough wiggle room with the timing pins in the magnetos to put the timing off by a whole gear tooth.  If it’s off in opposite directions on each mag, there might not be enough range to bring them both back into line at the right point.     But eventually, I got it.   The trick is pulling the prop backwards a bit, then advancing to see the lights go.   The prop has to be pulled backwards enough so that going forwards takes out the gear lash well before the points open, otherwise the adjustments are crap.   But you don’t want to go so far back that you catch the impulse couplers again.    Maybe this isn’t the proper way to do it, but this worked for me.  Also of important note: pull the timing pin out of the magneto before cranking the engine around.   If you don’t, best case is you’ll bend your timing pin like a wet noodle.  Worst case is you damage the innards of the mag.

So I got them as close as I possibly could.    Then I put the shielded ground wires back on.   For safety, the shielded wires go back on the P-lead and ground before the distributor caps go on, because until they’re on and grounded, the mag is hot, and if a spark is triggered, it could swing the prop and really ruin your day, especially if you or your stuff is in the prop arc.   Imagine that.  The prop kicks and sends a blade into the tank of your air compressor or a nearby tool cart.   Prop strike!   Have fun tearing down that engine, sunshine.

By the time this process was over, I was already well past my scheduled time to head back to Los Angeles.   But if you’ll remember, this exercise was only part of the day’s activities.   The other things I needed to attend to were the RPM sensor and the oil temperature probe.   Earlier in the week, Matt at MGL responded to my email and said I needed to remove the ballast jumper on the RDAC and that I could delete the resistor between 12v power and sensor signal.   I pulled the ballast jumper, then proceeded to push the ship out into the wind for a quick test.    Ron and Melody helped me push out and get pointed into the Santa Ana wind.   With the wheels chocked, I fired it up, once again.

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It lit right up, after Owen reminded me that I needed to run my boost pump for a second to get some fuel pressure on startup.   It ran strong and smooth, and I had an RPM reading this time, but like a monkey, I forgot to test each mag individually.  But here’s another ground run video:

This time, however, was another milestone.   We pulled the chocks and I actually taxied down to the end of the hangar row, then back.   At that point, my EGT’s were starting to get a little high, so I thought I’d quit while I was ahead.  We pushed it back into the barn and I went home.

Equal parts forward and back.

6 hours.

One of these days, I’ll move forward without moving backwards.  Today I had to dismount the EFIS in preparation for taking it to MGL Avionics.   Apparently the OAT module is fried.  I tried it with a new probe last week, no dice.   Maybe, if I’m lucky, I’ll be able to drop it off tomorrow on my lunch hour.   Other than that annoyance, I got the tailwheel hardware primed, something I should have done long ago, and I got my spark plugs torqued in.   But now, for some mysterious reason, the tailwheel steering chains don’t reach their mounting points on the rudder anymore.   It’s possible I had the steering link on upside down/backwards, which would have accounted for the missing 3/4″ of chain necessary to bridge the gap between what I need and what I’ve got.   Looks like I’ll be ordering another set of tailwheel chains.  Grumble.

Anyway, once I get my EFIS back from the shop, it’ll be time to prepare the engine for first start.

On another note, I’m progressing nicely in my tailwheel training.   We flew from Torrance to Hawthorne, where I did 8 landings, unassisted.   Apparently I CAN land a Citabria in 3-point attitude.   At least when the wind is coming at me and I set up the approach right.

Prop Safety Wired.

2.5 hours.

This is pretty much what I did last weekend.  I was only able to get up to the airport for a couple of hours, and in that time, I had to figure out how to safety-wire the prop.   This is a necessary step.  The propeller needs to stay on, and it needs to stay on for the entire duration of the flight.  The way this is accomplished is with the ubiquitous safety wire.   The Hartzell manual calls for .032 safety wire on these six bolts and fortunately I’ve got half a spool of it still in my kit.

I lost count of the number of runs I took at this, but finally I got it right.   There are a couple of interesting parts to this.  First thing is to get the prop torqued to 65 ft/lbs.   Then you have to back the nuts off enough to get the safety wire through the spring pin.  Then you have to guess the length of wire you need after all the twisting happens.   They’re supposed to be wired in pairs, with the wiring preventing the nuts from backing out and causing really bad things to happen, like the prop departing the airplane and leaving you with a not-so-gliding glider.

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As you can see from this next shot, I had a few attempts.   Apologies for the bad photos; as soon as you jam the iPhone up close to something in low light, its autofocus loses its mind.

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Productive couple of days.

19 hours.

Yeah, that’s Thursday, yesterday, and today.

The pieces are going on the plane now.   I installed both wingtips and did the accompanying wiring.   Of course, like a moron, I severed the GPS antenna wire while I was crimping a connector for the wingtip VOR antenna, but Jim had an extra one and I was able to repair the GPS cable and install the VOR antenna cable

 

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I also installed the strobes and new strobe pack.   The bright white flash is the strobe actually working in the left wingtip.

 

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One of the neat things about Oxnard airport (and presumably Camarillo) is that you often get treated to flybys of things like this restored B-25.  Weird stuff passes by outside my hangar just about every day, and I love it.

20130629-172558.jpgThis is the wingtip, showing the landing light and nav light working.

20130629-172608.jpgBoth wingtips on here.  I spent a little time peeling the remaining blue stuff off the tail, and I just need to get it off the bottom wing skins and the plane will be blue-stuff-free.
20130629-172632.jpgHoisting the prop out of the shipping crate, hopefully for the last time.

 

20130629-172659.jpgProp is on!
20130629-172722.jpgToday was about the prop.    I tried to get it done yesterday, but there was a flight, a barbecue, and the need to get home for evening plans, so I wound up doing it today.   Today was not all that wonderful.  There was an accident at the airport and I don’t have any details, and won’t publish them here until more is known, but it appears that we’ve lost a really good guy and a wealth of knowledge of experimental aviation and RV’s in particular.   Yesterday he lent me a torque wrench so I could torque the prop bolts, which I did today, along with the spinnner.

 

More odds and ends

4 hours.

A few things here and there. I installed the MAP tubing and put a couple of heat shields on the pipes to protect the throttle and mixture cables. I also installed the canopy seal, which is going to need some assistance from some RTV or proseal. I do think firewall forward is just about done, though. The cabin heat SCAT tube rubs on the engine mount a little, but some UHMW tape should fix that. The two things I did that were of major importance were the autopilot test and getting that ridiculous piece of lead off the flange of the left elevator counterweight rib.

A while back, I’d balanced out my elevators, or so I thought. You’re supposed to put the elevator tips on, then drill holes in the lead weight until the elevator balances. Well, guess what? You’re not supposed to have the elevators connected when you do this. I discovered this, freaked out, then riveted a flat piece of lead (cut from an extra counterweight) to the outboard rib.

When I put that away, thinking I was just about the smartest cat in the whole barn, I started imagining the kind of beating a control surface takes in flight. So what happens to a little piece of lead riveted to this structure with a couple of Cherry countersunk blind rivets? The piece of lead comes off and somehow jams the elevator in the dive position and I go screaming downward like a holed Stuka, straight into a busload of orphans on the 405. This has bothered me for months, but I could never find a good opportunity to fix it until Saturday. I drilled out the rivets and put the lead back in a drawer. I also read about a neat trick you can do when balancing your elevators: Pour some lead shot into the tip through the tooling hole in the rib until th elevator balances out, then stick it in place with epoxy resin. Even if it’s not perfect, bias it a little heavy, because paint will change the balance.

I also mounted the MGL GPS antenna on the top side of the glare shield. It works; I get an intermittent GPS position while still inside the guest house.

Oh and one other thing: I dragged the wing cradle over to the shop and tested out the bank servo of the autopilot. Since I actually followed a wiring plan and wired the fuselage-side and the wing side according to it, I was able to test out both servos simultaneously. I do need to make a new ground connection though. The ground from the servo bracket sucks and I was only able to get a good ground by cleco-clamping the ground terminal to a wing rib.

The Skinner

3 hours.

And yes, it’s a shout out to Neal Asher, whose writing has gotten me through a tough couple of months. When you’re having horrible-seeming things happen to you, reading about truly horrible things happening to somebody else and the truly horrible people who cause them getting their comeuppance is very therapeutic.

As far as this aircraft project goes, yesterday was not horrible. I actually might have the temerity to call the firewall-forward process almost done. The only two things missing from the equation is a 2″ hose clamp for the cabin heat SCAT tubing (which is actually missing, I can’t find it right now) and the manifold pressure sensor fitting and tubing, both on order from McMaster-Carr. I can look at the engine installation and say with fairly high confidence, yes, this engine will turn the propeller repeatedly. Today I’ll go through my periodic shop purge/clean ritual and see if the clamp turns up.

I also took a long look at all the stuff just behind the firewall and ahead of the subpanel, to make damned sure there was nothing else I needed to put there, because as I’ve mentioned before, once you rivet that top skin on, you can’t get to anything below it without a flashlight, a mirror, and possibly tentacles. Satisfied to the limits of my ability with such things, I began riveting the top deck skin on. This is hard. This is hard because you have to have a rivet gun on one side and a bucking bar on the other, separated by a 3-foot sheet of metal and ‘awkward’ only begins to describe the process. There are two holes in the subpanel support capable of taking my hand holding a bucking bar through them, and it’s a little like the reverse of a monkey trap. There is much maneuvering into position, then there is riveting, whilst holding the bucking bar perpendicular to the rivet without being able to see it. This process enabled me to do the center row of rivets, and the canopy hinge support bracket, but failed on the outboard subpanel support rivets because to get my hand into the right position, I had to bend the skin away from the surface it was being riveted to, causing a gap. I couldn’t get the leverage I needed and the skin ‘pillowed’ on the support rib. Bah. Curses. Foiled. I’ll need to enlist a helper for this step, but as soon as it’s done, I can put the canopy back on and officially list the project as ‘more parts assembled than not.’

The endless detailing.

5 hours.

I’m getting real tired of posting about loose ends, but at this point in the build, that’s pretty much all there is. I spent the day safety-wiring and adel-clamping various things firewall forward. Oh, and I did get the blast tubes done for the magnetos and alternator. These are pieces of ribbed conduit that go through the baffle wall and blow air directly on things that tend to heat up. I installed and safety-wired the tachometer drive cap, the oil drain plug, the governor clock screws, and a couple of other odds and ends. Safety wire is crazy stuff and hard to work with, especially in tight spaces, but after a while you get the hang of it.

I secured the wiring bundle on the right side behind the firewall with Adel clamps. It was loosened up to do something, I forgot what.

Oh, and the wonderful news is, we’re now ready to rivet the top deck skin on!