ORIGINAL: ameyam
I have been grappling with this problem for over a month now. I have already replaced the fuel lines thrice and this time around I pressure tested the lines for leaks before I put them in and on the tank. So pressurisation problems can be ruled out.
No it can't.
I've heard a bunch of people make exactly the same arguement with exactly the same "engine dying in flight" problem...
But I've found plumbing problems in about 60% of those situations... things which the pilot was SURE is correct, but it turns out there is a leak or some other problem.
Don't rule out ANYTHING until the engine is running correctly.
ORIGINAL: ameyam
No compression means no compression. I found that at that critical temperature, the prop simply turns over by finger. You dont even get the push-back you are talking about. Let it cool a couple of seconds and the compression returns. Loss of compressio seems to be happening a bit randomly.
When warm you should feel some resistance at TDC if not, check your cap screws on the cylinder head.
I'll bet what is happening is that as the engine is getting ( overly ) hot ( because it is too lean ), the head expansion is letting air blow past the cylinder head, resulting in the low compression.
Get the engine to the point it does this then tighten down the cap screws.
It's normal to have to do this after the first few flights. The cap screws get VERY loose at first.
ORIGINAL: ameyam
Remember I have already got black oil in the exhaust two or three times within 3 weeks and I have already checked to ensure that everything is as tight as feasible.
Which may mean you are burning too much oil, though some black oil in the exhaust is not unusual dependant upon the fuel you use.
What are you using? Synthetic or Castor?
ORIGINAL: ameyam
When I take-off, it runs for a couple of circuits and then deadsticks. This is with the needle set rich and with the stock muffler and with a 13x6S2 prop doing only level flying.
A 13x6 on a .55 AX seems a bit big to me. I run 13x6's on higher power .75 2C engines. My .61's use 12x6 props.
Step the prop size down to what is recommended until you've resolved ALL problems.
ORIGINAL: ameyam
Both times this weekend I could tell that the engine was about to deadstick because I could hear the rpm wavering in the air. And everytime I heard the waver, the engine cut-off in less than a few seconds.
While it is very likely running too lean, or leaning out in flight, it does not sound like the cylinder is seizing because of the heat.
Again check your cap screws when the engine is hot, all of them, but particularly the head screws.
Also did you rebuild the head at some point?
Is it possible you put things back together incorrectly?
ORIGINAL: ameyam
Think I have eliminated most of the variables.
Famous words often spoken right before a crash... you MAY have but never assume so until the problems are gone.
Another famous line is "Watch this!".... crash...
ORIGINAL: ameyam
Please suggest if I have missed something, I will try that out as well. Point is, I want to replace the engine while I still have the airplane intact.
Until you've discovered the problem, introducing a new one ( e.g. a new engine ) may just make things worst.
The AX is a good engine and should not give you these problems unless something is amiss.
BTW: Look for nipples that have broken. Remove the nipples clean them and put a bit of thread lock on before re-installing.
Be VERY careful not to overtighten. They go on snug, but they strip very easily.
Also check the muffler nipple. Often it can become clogged with sludge, killing tank pressure and causing what you are seeing.
ORIGINAL: ameyam
Still, if I do put in a 75 or a 91, I will use a lower pitch prop- 14x4 or so. I dont think a 15'' will fit. And I am planning to use a Dubro anti-vibe beam mount I already have to prevent too much vibration stress on the airframe. In any case, I never use full rpm on my airplanes even at take-off as it is simply unnecessary- if you have sufficient take-off run it will lift itself at 60% throttle.
Put a smaller prop on the .55 AX. This will reduce the load and the heat build up. You may simply be running it too hot.
I use a laser temperature guage to make sure I'm not overloading my engines.
If the temp climbs above 310 degrees around the plug after WOT for 5 minutes, I KNOW I'm either running the engine rich or with too much load.