Author Topic: OS .46 LA question (Read 1222 times)

Kirm Dog · « **on:** August 20, 2006, 05:36:37 PM »

I have an OS .46 LA that's about a year old and probably about 5-6 hours of run time on it. My problem is in the last few weeks starting the engine,on the ground I have it running around 9800 with a 11-5 APC prop. In the air after the first wing over or loop it starts running in a real sloppy 4 cycle and the lap times go way up along with the loss of line tension. I had thought that it was the rear NVA and plastic back plate. I put in a PA NAV new venturi and a metal back plate with a new gasket and a little silicon on it. Still the same run, sounds fine for about 4-6 laps then into a sloppy 4 cycle. I cleaned the tank, changed the fuel filter, fuel lines and have been using the same fuel all the time. For an engine that always use to run great, this one has me stumped! Any ideas?

Bill Little · « **Reply #1 on:** August 20, 2006, 07:08:15 PM »

Hmmmmmmm.................

The opposite of runaway! Never had to deal with that particular problem.

I would check the head and any gaskets present there. Sounds like as it gets the heat built up, something is happening. Try a different plug. Also check for any cracks in the crankcase.

Trying another jug of fuel, or type of fuel might be another correction.

Good luck, Don!

Bill <><

Kirm Dog · « **Reply #2 on:** August 21, 2006, 09:14:15 AM »

I think I would be in better shape so to speak it the engine started out rich then leaned out. I will check the tank once again but I think it's still in the same position. I had wondered if there might be a crack in the crankcase Bill. I was thinking that when the engine is cold it's fine but it seems like once it gets warm it goes rich, does it have a crack somewhere that opens when hot? Athough wouldn't it do the same thing on the ground? It doesn't seem to do this if I run a tank through it on the ground which would make me want to believe that it has to do with the tank somehow.

I'm so confused

Don Kirmess

Steve Fitton · « **Reply #3 on:** August 21, 2006, 10:06:51 AM »

Funny you should mention an LA-46 mysteriously going fat.... I had trouble with that very problem yesterday......

Mine has not been going dead rich, but just fading a little bit rich off the takeoff needle setting the last few weeks. Since the airplane was marginal on power already, any loss late in the pattern was critical, and eventually fatal.

I tried to fool the engine yesterday by switching the tank venting from uniflo to standard venting, which reduced but did not eliminate RPM drop off and ultimately didn't work.

My engine was a moderately well used motor from another airplane, with approx 280 flights. I do consider John Tates comment on this isue on the SSW version of this thread to be intriguing. When I put this motor into the Avanti, I pulled the head off to add a shim and was suprised greatly to see the glo plug almost completely obscured with some sort of sintered on looking dark material. Presumably carbon, but I've never seen a carbon deposit that big in so few flights, or piled on the top of the plug like that. I wonder if my liner was shedding nickel. I looked at the liner and saw no obviously peeled areas, but when you shine a light on the liner, from certain angles the silvery looking nickel seems almost translucent and the liner has a brassy tinge to it. I haven't taken enough LAs apart though-maybe they all look like that. Tates engine he mentioned in the other thread had an out of round condition from the factory and grenaded the P/L in only about 30 flights, so that was a different case.

Liner issues (or not) aside, hopefully there are some ideas to fix this problem when it does occur. My problem was much more subtle then going dead rich, but just as annoying and puzzling to figure out.

Steve

Kirm Dog · « **Reply #4 on:** August 21, 2006, 12:55:49 PM »

Steve;

It sure is annoying!

I could do 8 minutes of level flight and it's just like clockwork. On the 4-6th lap it will go dear rich. Doesn't matter if I'm doing a pattern or not. Mine also started doing it very mildly at first but now it's a pain in the you know where.

On the other forum it was mentioned that it may be a hole or split in the tubing inside the uniflow tank. I've pressure tested the tank several times and and it was fine. In the next few days I'll pull the back off and see what's happening inside.

Don Kirmess

Dick Fowler · « **Reply #5 on:** August 21, 2006, 03:42:29 PM »

I would think that a crankcase leak would more likely cause a lean condition as the fuel draw is reduced by loss of "vacuum" in the case. Also tough to get a needle setting.

I wonder if it might be a condition of the prop unloading in the air and the loss of heat in the combustion chamber puts the engine a wet four stroke. I've run an 11X5 APC on a couple of .46LA's and they seem happier at around 10,200 to 10,400 at launch. 9800RPM would be a pretty wet needle setting for my engines. So it maybe that you are launching on the wet side and it just goes to real rich when it unloads. I also prefer an 11X4 and spin them up a bit.

Plug problems will also create the same condition. Try something on the hotter side. Again most of the guys in our group use Thunderbolt FS plugs. http://www.hobbypeople.net/gallery/115490.asp

rustler · « **Reply #6 on:** August 23, 2006, 04:37:34 PM »

It is just possible that the p/s is getting worn out. These engines are made for r/c fliers who demand just to take an engine out of the box, put it in a model, and go fly, setting the engine to max revs first flight, which can possibly also mean a lean setting. As such they are set up real loose in the first place. It's possible to grasp the threaded portion of the shaft on a new LA and turn the engine through 360deg. (with no plug in the engine). Try that with a quality dedicated ABC/AAC stunt motor. This is not to denigrate O.S. - they are masters at providing what the customer wants, it's just that they cater for the mass market which is r/c.
You may just have a good windy weather engine, - sounds like it ain't going to wind up much!

Kirm Dog · « **Reply #7 on:** August 26, 2006, 01:46:09 PM »

Well guys, here's what's happening. I've done everything posible tocheck this thing out. New NVA, new glow plug, new backplate, pressuer tested the tank, pulled the back of the tank off and checked the tubes inside the tank, resoldered and pressure tested again, Nothing! still wouldn't run right. Then last night in bed (I do my best thinking just before I fall asleep but most of the time I forget what it was) I was thinking, what if I got a bad glow plug? could it be possible that the idler bar was keeping the engine running if the coil was going bad? Well I replaced the glow plug this morning before my first flight and BINGO! The engine runs just like it always has. Good runs all day today. I guess it pays to check the simple stuff a couple of times first before moving on. Live and learn I guess.

I want to thank all of those that gave suggestions. If nothing else it gave me a chance to eliminate those things and take any dought from my mind.

Don Kirmess

Author Topic: OS .46 LA question (Read 1222 times)

Kirm Dog

OS .46 LA question

Bill Little

Re: OS .46 LA question

Kirm Dog

Re: OS .46 LA question

Steve Fitton

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Kirm Dog

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Dick Fowler

Re: OS .46 LA question

rustler

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Kirm Dog

Re: OS .46 LA question