« Archives in November, 2013

Odds, ends, and annoyances.

6 hours.

Last weekend I had to work to deliver a product launch, so no airplane.   This weekend, I had a list, and I knocked out a bunch of stuff on it.  To sum up:

  • Tensioned and safety-wired alternator bracket
  • Removed protective plastic from aft canopy and removed tape residue
  • Relabeled mag switches and made “OFF” labels for everything else
  • Reconfigured quadrant for extra travel on governor
  • Added a wider heat shield to protect the throttle cable
  • changed out a too-short bolt on the purge valve cable bracket.

Apparently the way you do alternator belt tension is by increasing belt tension until it takes 12 ft/lbs of torque on the alternator nut to slip the belt.   That’s it.   That also gives you the 1/4″ deflection (on a new belt) called out by the usual procedure.   This is important, because a slipping belt can cause over/under voltage problems.  I did that, and safety-wired the bracket tension bolts together, like so:

Alt bracket saftey wire

Alternator bracket Safety wiring


When I put the aft canopy in all those many moons ago, I left the protective plastic on it, because why not?  Why subject the vulnerable plexiglas to my fumbling ministrations while I’m climbing in and out of the tailcone to adjust one thing or another, swinging tools and wires about?   Because once the canopy is attached, it’s difficult if not impossible to get all the plastic out from between the roll bar support and the canopy.   I had to put a space heater in the cockpit and run it for a while, until it was a balmy 75 degrees and the plexi and surrounding aluminum were warm to the touch.  I took out all the fasteners and removed the aft canopy section, which I put on the bench, then removed the rest of the protective plastic and cleaned off all the tape residue I couldn’t get to before.  100% better.

Protective plastic and tape residue gone

Protective plastic and tape residue gone


The magneto switches on the panel were cryptically labeled “MAG 1” and “MAG 2.”   I don’t know why I thought this was a good idea, and it broke with common practices in aircraft UI/UX design.   I relabeled them “L MAG” and “R MAG” because that made the most sense, and that’s how everyone else does it.   While I was in a labeling mood, I made about a dozen or so “OFF” labels to describe the down position of most of my toggle switches.   The double-throw switches like flaps up/down already had good labels in both directions, but there wasn’t anything labeled “OFF” anywhere.  The switch pointing toward the function described seems obvious to me, but apparently it isn’t to whoever wrote that reg at the FAA, so now everything is labeled according to the AC’s.


Like I said, there were odds, ends and annoyances.   Firewall forward, there was the matter of a heat shield, a too-short bolt, and the prop governor travel.

Heat shield on throttle cable

Heat shield on throttle cable

I did have a shield in place at this spot, but I remembered I had an extra double-wide one, so I put that one on in its place.  On the topside of the engine, I changed out the bolt holding the purge valve cable.   It was a temporary thing when I did it, and it didn’t have the required number of threads showing to meet spec, and since it’s pretty important that the purge valve remain closed in flight, it’s also important that everything connected to it is not half-assed.  This is what the proper bolt length looks like:

Purge valve cable bracket

Purge valve cable bracket

As to the prop governor, if you’ll recall from last time, the prop didn’t cycle at the low end of the throw.  The quadrant was only moving the lever arm about halfway through its arc of travel.   The simple fix to that was to drill a #12 hole about 5/8″ up the quadrant lever from the original one and voila, I get me 75-80% travel instead of 50%.   That story ended with a quick runup to 1800rpm and getting the prop to cycle, so that’s good enough for now.   Whether or not I have the rpm set right due to the arm position relative to the governor shaft is another story, and it will be resolved on either a full power run or first flight.  Even so, the engine is more responsive, now that it’s firing on all the plugs, which are now more or less synchronized in their ignition, so that’s a plus as well.

What was really awesome about this weekend was that for the most part, it was forward motion, not playing catch-up.  New things got done and good fixes were made, rather than unsuccessful stabs at a persistent and difficult problem.   There’s still a bunch of stuff to do to get ready for first flight, but I think if I can keep up the pace, I’ll be on track to fly it in early 2014.


Magneto repaired, on to restraint system

6.5 hours.

Within minutes of arriving at the airport this morning, I replaced the distributor block assembly and the distributor gear in my right magneto, the one that’s been sitting on the bench for a couple of weeks.  It was a complete non-event.  I got the new distributor block out of the box, put the timing pin in it, installed the new distributor gear, lined it up, and screwed it down.   Done.

I put it back on the engine, did the buzzbox test again, and got them both lined up dead nuts at 20 degrees BTDC.  Of course, the proof is in the pudding.   I wheeled it outside and fired it up.   It ran just fine, of course.  Equal rpm drop on both mags, and nice smooth running.

The other little issue I need to work on is the prop governor.   I set the arm to what it was when I got it, based on a previous photo.   In that position, it doesn’t cycle the prop all the way to coarse pitch.   Makes sense, the arm can only move about half way, given the cable end’s position on the quadrant.   I’m going to have to drill a hole  another 3/4″ up on the lever arm to get that extra throw.

After the quick runup, I shut everything down and pulled it back into the hangar to put back all the stuff I’d discombobulated during my clownish magneto debugging.   Wires got wrapped, nuts and screws got torqued, and everything went back to being a proper firewall-forward configuration.   This took a bit of time, but it really wasn’t too bad.

One of my goals for today was to work on the seat belts.   Seat belts are pretty important.  They keep you from becoming one with the instrument panel in the event of an impact incident.   Mine are some nice gray Crow 5-point harnesses with a cam-lock release.   Like so:

Obviously, some adjustments need to be made, but I think they’ll work pretty well with the seats.    The bolt holes in the attach ends are pretty big, so to get them to work with AN4 bolts, you have to fill them with something.   AN960-416 washers work pretty well, but they need some adjustment.   For them to fit into the attach holes, it’s necessary to shave off some of the outer edge material.   This is best done by putting a bunch of them on a bolt, chucking the bolt into a drill press, and running a file along them as they spin.   Then you can press-fit them into the seat belt attach holes (if they don’t just fit), and everything’s cool.   The only thing missing here is the crotch strap,, which I have to take the floor pan out to install.

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:


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.