Interject when you figure out my underlying
issue. Please!
It started about a year ago. I was
putting a lot of hours on N4VY (Turbo rotary RV-6)
commuting for work. One day I flew to Ramona to meet up
with my formation flying buddies. After the brief we
went to start our planes but mine wouldn't start and I
had to bow out of the flight. It would crank and almost
catch, but I wore out my battery trying. After
recharging for a couple hours it started up normally. I
flew home and wrote it off as some sort of start
procedure SNAFU. I use Tracys EC2.
But that was the start of a long
succession of difficult starts when pre-warmed, starting
fine when cold. Sometimes leaving me stranded at a gas
stop until the engine cooled. While in a safe place I
tested air starts and there seemed to be no issue there
just turning the fuel pumps back on with the prop
spinning.
Then it started doing something else
strange. After starting it would run really rough
whenever the alternator output got above 55amps or so.
By rough I mean sputtering and resisting advancing the
throttle by sagging and occasionally backfire. If I had
been cranking for a long period it could take a minute
for the amps to drop and the engine to run normally.
I started by checking for loose wires and
replacing the spark plugs. (No improveement)
So then I replaced the battery, it still
seemed strong but maybe the voltage was dropping with
cranking or somethng. I got interested in Li Ion
batteries and splurged on the Big one. It increased my
total enerrgy storage, CCAs, and decreased weight by
over 10#. Expensive but worth it considering they are
also supposed to last longer.
But it turns out the old battery was fine
after. Not only did it not solve the problem, but
because the Li Ion battery can take a much faster
charge, it would max out the alternator at least briefly
on EVERY start, making the problem worse.
Next was fuel filter and spark plug wires,
no improvement.
The condition continued to slowly worsen
despite trying richer mixtures of 2-stroke oil and or
MMO. So I finally grounded it.
My thought at this point was that the
compression had finally deggraded to the point where
compression was not enough for combustion unless turning
really fast. Perhaps the extra drag from full output of
the alternator made the condition worse. And when it
was hot the rotor housings expanded just enough to
really kill the compression. The side iron plates in
that engine had the better part of 1000 flight hours
plus unknown time in an RX7. Compression measured mid
20s on both rotors, for what thats worth. Time for a
rebuild.
I went all out. All new rotor and side
housings, seals, springs, o-rings and the necessary
aircraft mods to those parts. (fittings, etc..., EGR
passages pluged) I also replaced the LS1 coils and the
coil harness.
And? Nothing. Fuel flow and injector
gross function verified. All sparks verified during
cranking with a timing light. Tried a different CAS
just for kicks. The engine is a little tight because it
is new, compression is not spectacular cause the seals
have not set, perhaps the apex seal little bits are
still glued on..
Jump in here anytime.
You know? You are right, I just need to
disconnect the alternator and keep cranking until it
finally catches and gets a little bit of a break-in.
This talk has been really helpful for me.
Dave Leonard
(the forever optimist)
Also going to switch to full synthetic
2-stroke oil without MMO. The new engine will never
know how good it has it.