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.