Yeah... yeah... I forgot to mention that the bad idle doesn't matter if the glow driver is connected or not. My mistake.
See if leaving the glow driver on helps.
But I'll have to try the pinch test bit; I saw that earlier and made a silent 'you know, I'd better try that.' Thanks for the reminder.
There may be an issue with the o-rings on the mixture screw, where no amount of adjustment will do much.
I'll do some searching to see exactly what you mean (I have a vague notion of your meaning at the moment... it's actually rather possible, now that I think of it. -- details at the end.)
What led to having to rebuild the engine -- having to replace the con rod and the ring?
Short answer: Something bad.
A somewhat more informative answer is: Something really bad that I'm almost too embarassed to mention.
Did you have to replace any other part?
For good measure, I did replace the gaskets (head and backplate). So I do know they are in place. (I remember specifically verifying this when putting it back together).
When you reassembled it, did you put the head gasket in between the cylinder and the head?
See the above answer.
for what happened to require rebuilding it...
Before starting, I'll state that I took the rough-running engine and put it away, using an entirely new OS .50 in my helicopter from that point on. Then I got a new helicopter, and thought to save a few dollars by rebuilding the old one...
About a year ago (which is when I trashed it), I was just getting into the hobby; having read "Ray's Authoritative R/C Helicopter Manual," I decided to break in my engine on a bench. Part of this is because I knew exactly squat about tuning in general, so it sounded like a reasonable thing. (Better to learn something about how to tune the engine with it on the bench than to worry about it when I have a spinning rotor blade to concern myself with).
That part went well.
Well, I wanted to verify a few things were OK when I put it in the heli. So, I pulled the main blades off, and spun up the unloaded head. I wasn't paying attention to the RPM's at this point, let alone the fact that the engine was running completely unloaded.
And, suddenly - it stopped dead. And it was very, very, very hot. I didn't have a temperature instrument handy, so how hot it was is anybody's guess. It took quite a while to cool down (5-10 minutes).
I then pulled the engine (out of the heli) to see just how badly I'd screwed things up. I took off the backplate, and received a definate conclusion: The connecting rod had become deformed so that its nice round hole (where it connects to the crankshaft) was oval, and then shattered. The broken pieces were fairly large (usually larger than a few millimeters on a side) As the crankshaft spun around to the (now shattered) connecting rod, it stopped dead.
After carefully cleaning out the crankcase, I started to carefully disassemble the engine. When I pulled off the cylinder head, there were no bits of metal inside. (I'm young, and have pretty sharp eyes, FWIW).
The cylinder lining came up with almost no effort. (The piston came with it, since it wasn't attatched to the crankshaft anymore). There were a few (about 5 or so) bits of metal in one of the intake ports -- near the crankcase, about 1/4 of the way to the actual intake in the cylinder sleeve. They were also too large to have fit into the holes in the cylinder sleeve anyway.
I carefully removed the piston, and found no scoring of any kind in the cylinder wall. The piston was likewise undamaged. (using a magnifying glass).
The piston ring had a tiny chip in it probably 0.25 mm, on the top outside corner of where the ring is split-- but this may have been from my uncautious sliding of the piston back into the cylinder for storage while I waited for the connecting rod to get shipped in. So I replaced it as well.
So, basically, this engine has been damaged badly already, and I'm mainly seeing if I can resurrect it. (It's also why I have a new OS .50 Hyper sitting in its box on my desk). I want to try to resurrect it almost as much as a hobby project in and of itself -- not because I want to save a few bucks.
Which actually leads me to think I should just replace it with the new Hyper, and just have the engine by itself (on a bench) until it's actually reliable enough to run in a heli... Although it hasn't quit on my yet, that doesn't mean it won't...
If there may be an o-ring problem, it may be due to it partially melting from the heat caused/resulting from the connecting rod breaking.
The last thing I want in a heli is a few loose screws.