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HelicopterEngines Plugs Mufflers Fuel › OS .50 SX-H idles really rough
04-03-2005 09:37 PM  13 years agoPost 1
pariah

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South Jordan, UT - United States of America

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I've got an OS .50 SX-H, attatched to a MPII (and my Sceadu).

The engine runs fairly well (not quite as smooth as I'd like, but I'm still in the 'break-in' phase.)

But it's idle is ugly. Really ugly. Nothing at all like the other OS .50 I have (or like this one used to have before I had to replace the connecting rod and piston ring. -- and, yes, I do know that it's assembled correctly, with the notch in the ring lining up with the little pin on the piston, etc, etc.)

I've tried adjusting the low-speed needle valve, but I am not sure how long it takes for these changes to take effect. (while at idle, of course...)

I will say that no matter where I put the low-end needle, it didn't seem to make a difference at all in how rough the engine idled.

On the positive side, I have the high-speed needle set about right (slightly rich, but only 2-3 clicks).

Does anybody have a suggestion on what can be done to smooth out the idle?


--
The last thing I want in a heli is a few loose screws.

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04-04-2005 12:28 AM  13 years agoPost 2
Al Magaloff

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12,199 Posts- Enough Time Wasted. See Ya!

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What is the high needle set at?

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04-04-2005 04:31 AM  13 years agoPost 3
rcheliflyer

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calif., usa

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How's the idle speed, set it bit high and adjust the mix a bit, then hover
land and recheck, go back and forth till it's good on the fuel line pinch test maybe a couple of sec before the rpms increase.
You might try an Enya 3 glo plug as they work pretty good keeping
a rich idle lit.

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04-04-2005 04:44 AM  13 years agoPost 4
dkshema

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Cedar Rapids, IA

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OS 50 SX-H manual. You say it's a 50 SX-H, not a Hyper....

http://www.osengines.com/manuals/50sx-h-manual.pdf

I'd suggest you start with the factory settings again on pages 12 and 13, then jump to step C on page 16.

You may be trying to idle too slow and are trying to correct with the mixture screw, instead of adjusting the initial idle speed using the throttle trim. Once you get a decent idle with the trim setting on the TX, then check the transition to mid-range. Tweak the mixture screw (the one that is on a cam and that runs that forked plate) to get a good transition.

Then go tweak the mid range using the needle valve. This should get you a decent idle and transition, and good mid-range. When you get that going well, tweak the top end using the needle valve, then go back and fine tune the two needles.

I've got a 50 SX-H on my EVO and the MP2 quiet version. The idle is smooth, the transition is good, and the top end is great.

Dave

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04-04-2005 06:09 AM  13 years agoPost 5
pariah

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South Jordan, UT - United States of America

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I seem to have created some confusion here...

It's got a stock carb -- so it has the main 'high speed' needle, and the second 'mixture' screw.

Um... returning the engine to factory settings is the first thing I did before even attempting to start the engine after the rebuild. On both the needle valve and the mixture screw.

The only way the engine will idle at all is with a very fast idle (almost to the point where the clutch engages on the Sceadu). Since I can't really say how many engine RPM's that is (since the blades aren't spinning), I can say this: The carb venturi is open about 20% from closed. If I give the trim 2-3 more clicks, the clutch starts to engage on the Sceadu. I'm definately not comfortable with that idle speed, as on my Rappy, I'd have to keep a good grip (with both hands) on the heli to keep the head from spinning.

The idle is easily 2-3 times faster than that on the OS .50 in my Rappy.

The throttle response is fine -- doesn't hesitate in the transition to mid/high speeds, doesn't burble in transition in the transition from high to lower speeds.

And I also know what happens with this engine if it is running any richer than it currently is: one transition to higher RPMs hesitates.

Two, the engine reverses directions when at idle. More accurately, it reverses directions at factory settings, which are horribly rich at my altitude.

Leaning the engine out (needle valve, not the mixture screw) to a considerably better tune fought off the reversing of the engine (as well as throttle/transition response in both directions) -- but the idle smoothness never changed.

The needle valve is about 1 1/3 turns out from closed, the mixture screw is exactly where it is on my other OS .50 (and I have never touched it, never needed to). The mixture screw is also exactly where the factory default is on my new OS .50 Hyper (and I'm holding off installing it for now).

I keep very close tabs on what the engine's transitions are when opening and closing the throttle. Putting the engine into throttle hold results in a smooth, quick transition to idle from FFF, and re-engaging the throttle results in a smooth, quick transition back to speed. I also keep track of the engine's temperatures during the flight, and it never tops 210 °F (venom on-board temp monitor)

As my original post stated -- it runs fine at speed, but its idle is absolutely terrible.

And, as a note to make things interesting -- when the engine reversed directions, the engine actually started running much, much smoother; so it actually has a nice smooth (if fast) idle when in reverse. (Which actually became a decent warning that I needed to check if the engine had reversed)


--
The last thing I want in a heli is a few loose screws.

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04-04-2005 10:15 AM  13 years agoPost 6
Al Magaloff

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Sure sounds like the low is way too fat. See if leaving the glow driver on helps. The pinch test should tell you the story. Motors reverse direction when they are rich and too slow. There may be an issue with the o-rings on the mixture screw, where no amount of adjustment will do much.

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04-04-2005 01:10 PM  13 years agoPost 7
dkshema

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Cedar Rapids, IA

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What led to having to rebuild the engine -- having to replace the con rod and the ring? Did you have to replace any other part?

When you reassembled it, did you put the head gasket in between the cylinder and the head?

Dave

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04-05-2005 01:47 AM  13 years agoPost 8
pariah

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South Jordan, UT - United States of America

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See if leaving the glow driver on helps.
Yeah... yeah... I forgot to mention that the bad idle doesn't matter if the glow driver is connected or not. My mistake.

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.

Now 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.

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