DMcQuinn

My Feedback: (13)

This has happened about 6 or 7 times now and I'd like to know what the experts think may be happening. After about 15 minutes in the air, the engine loses about half its power and sounds noticeably different, like it is firing only on one side or is misfiring badly on both sides. It happens pretty much all at once and I set up and land within a minute or so. Today, taxiing back into the pits, the motor quit so I quickly dragged it back and restarted it in the pit area. It started and ran fine. I ran it at full throttle for about 20 seconds and it ran fine. After shut down from full throttle, I measured the cylinder temps. Left side was 250 and right side 230.
This has happened several times over my last few flying sessions. If I am only in the air for less than 10 minutes, the engine runs fine. Every time this has happened, it was toward the end of the flight (I use a transmitter timer and it has always been around the 15 minute mark). I replaced the tubing in the tank, thinking it may have a leak. No help.
Also, I think the engine is a little weak overall. Before this week, I was running a MSC 27x12 prop and getting 5700 max rpm. I opened the HS needle valve to drop the rpm to 5400. Then at the advice from this forum, I replaced the prop with a 3W 27x10 wood prop. Now my rpm is up to 5760 with this prop (left the needle valves as-is). I suspect the peak rpm would be around 6000 but I did not have time to re-adjust after the prop change today.
After 15 minutes of flying, my tank is about half full, and with the new tubing, I do not think it is drawing air. I have looked for air leaks that may happen when the carb block gets hot.
Because it only happens after 15 minutes, I suspect it is heat-related. Also the cylinder temps seem a little high. I have decent baffling, I think. Outside air temp was about 75. I use Amsoil 100-1 and the engine is 4 years old with 30 or 40 gallons run thru it. Using regular pump gas, purchased this week. I am pretty sure I am a little rich on both the low and high speed needle valve. One time a year or so ago I sent in the engine to Cactus who returned it with a note about "stuck rings". What are the symptoms of stuck rings? Can you tell by behavior of the engine or do you need to remove the muffler or the cylinder? For ignition, I am using a 2-cell Lipo with a 5.7 V regulator, I was having the same problem with a 4-cell 1400 mAh NiCd before I switched to LiPO. I don't think it is the battery because after the engine cools off between flights, it will run good for another 15 minutes until it happens again. And the battery tests out OK on my tester even after several flights (I use a 1000 mA load on my tester).

Diablo-RCU

My Feedback: (1)

You may have stuck rings again, which will give you low compression and low power. You could also have a bad bearing, which can give you all kinds of problems like inconsistent running and low power. If it were me, I'd pull the cylinders and have a look at the pistons, rings, to make sure they're free to move in the ring groove. Also check the crank for binding bearings.

RTK

My Feedback: (1)

You could be having a heat related failing of the ignition. Where do you have the ignition located?
Also re-adjust those needles.

DMcQuinn

My Feedback: (13)

The ignition module is on top of the motor box, under the cowl. It could get hot from the heat of the engine, I suppose. The bearings were both replaced a few gallons ago. I'll re-adjust the needles when I have more time. Today I only had a couple hours and spent most of it flying.

OSilfa

My Feedback: (2)

You have problem with the ignition for shure.
I have the same problem with 3w-24 and send the ign for check 2 times and in the service they tell me that the module is ok ,but its not.I change the ign module by other that i have of a 3w-42 and no more problems!!!!!


Oscar Silfa

DMcQuinn

My Feedback: (13)

Thanks, Oscar. I have always suspected that these ignitions may act up when heated. The cylinders are probably at maximum temperature within a few minutes of taking off. So if it was overall engine temperature, I would expect to have problems much sooner than 15 minutes. But I can see where it may take 15 minutes for the ignition module to heat up. I did have a problem once many years ago where the caps that connect to the spark plug would get soft and loose after being heated. 3W fixed this under warranty and the new caps have a different insulating material that has been better.

OSilfa

My Feedback: (2)

Yes,but your problem is not the cap and with the time the module is going worst.
Let me tell you that i lost my cap 232 findind the problem.Put the engine in stand and made too much test.

About the temperature 250/230 is not too high in groung dont'worried about it.
The only a can tell you is that the 3w engine need to be a little rich in the low neddle because when the engine get temperature he get the perfect mixing.this is the trick with the adjustment of the 3w engine,I have 5 of them

Swat Cop

My Feedback: (11)

I would bet you have a heat/ ignition related problem. I had a similar problems with my 3W150 mounted on my 40% Carden Cap. After exactly eight minutes the engine would go deadstick. I tried everything I could think of, the carb, all the lines, battery, carb block and nothing worked. My ignition module was mounted inside the motor box on the floor of the box. Finally I ran it on the ground and just like clockwork at eight minutes it died. I took the top hatch off the plane and ran it on the ground, ran though a full tank of fuel (about 15 min) and it never missed a beat. I put the top hatch back on and again it died at eight min. Replaced the module no more problems. If you send it in and they run it on a test stand there will be no problems and they will send it back and tell you its fine.

DMcQuinn

My Feedback: (13)

At this point, if I wanted to buy a replacement ignition unit, should I buy another 3W unit or a DA ignition. I understand they are compatible. Are there other choices?

HP^Matt

Your problems sound vary familiar to me. IMO 230/250 is too hot, I try to get closer to the 190 to 220 range myself. What I have found on the 3w 150's (new styles) Is that they like to develop leaks ....everywhere, case halves, base gaskets, carbs and phenolics/reed blocks. Basically anywhere where two pieces are bolted together they leak. Needles to say, I'm not too impressed with 3w twins at the moment. The quality in the case castings is substandard. I believe that the drive for a lighter weight engine has come at a high price. I know of 4 150's one of them being mine that has had to have plates welded to the backs of the motors because the mounting ears crack and break. One of these was from a crash, one had a hard landing with NO prop strike, and the other two broke on their own from normal use, one with only a dozen or so flights on it. The problem from what I can see is the lack of material in the mounting area, and poor quality casting (voids in the mounting ears). I recently was around a new 150 out of the box, and placed it on a true flat surface, it would rock back and forth like an annoying table in a cheap fast food restaurant. So if your in the habit of building nice flat firewalls to mount your engines to, you run the risk of breaking an ear off your engine by stressing the shorter mount of the 4.

Ooops, sorry I ran on like that.

Check your engine for signs of leakage around the case halves and base gaskets, and around the carb mounting area. If you are not using any ducting in your cowl, you might want to consider it. I havent seen a 3w twin yet that didnt benefit from it. Make sure there is pliant of room for the air to exit out the bottom of the cowl too.


My 150 is sealed up and running good now and I'm sure I will use it till its worn out, when that day comes I doubt I buy another unless the relationship between their heads and their rectums at 3w gain a little distance.

Good luck!
ME

DMcQuinn

My Feedback: (13)

Thanks for the advice. I have ordered an extra ignition module to have a spare. At least this way I can have a way to diagnose problems. My engine did have a pretty good leak under the phenolic carb block once and it did cause intermittent poor running. I have inspected for this situation and do not see any prolem in this area now. I will check all around the case for leaks. Is there any special technique you use to check for leaks? Or just a visual check of all the contact areas?

HP^Matt

On the ones I worked on, it only required a visual. They were wet and oily all around the case seams and jug bases. When I took them apart, the gasket surfaces were wet/oily where the leaks were.


ME

DMcQuinn

My Feedback: (13)

Thanks. About 2 or 3 weeks ago, I had it completely off the plane on onto the test stand to try to diagnose. I did not see any evidence of case leaking. Nor was I able to duplicate the problem on the test stand. Last weekend, I had three long flights (27 minutes, 22 minutes and 20 minutes) and the problem did not happen at all. This has only happened 6 or 7 times over the past few months and does not happen all the time. When it does happen, it has always been well into the flight.

HP^Matt

Definately sounds like an over heating problem to me then. Most likely two things going on, the engine is getting hot enuff to effect how the fuel and air mixes and combusts, which kind of starts a snow ball effect in engine performance. Plus as the others stated, the high heat around the ignition can cause operational problems too.

Do you have any ducting in the cowl to aid the airflow for cooling? What plane is it on by the way? I had an old style 3w 120 that was running a little hot at times, and was able to drop the head temps by 15 degrees by just altering the ducting a small amount. It was a 30min job that made a huge difference in how the engine ran on hot sticky 95 degree days.

ME

DMcQuinn

My Feedback: (13)

Just got back from the field. First and second flight each 15 minutes each and no problems. But on the third flight, at 14 minutes, the engine acted up again. Sounds like mis-firing or perhaps only running on one cylinder. I always set up and land within 30 seconds or so because the engine sounds so bad. I was 92 degrees today.
I have some baffles on top and bottom of the fins, so the incoming air must go through the cylinder fins. there is a fairly large area between the top of the cylinder and the cowl where the air could pass through and bypass the engine. In other words, the air could pass by the top of the spark plugs and not be forced through the top fins. I will improve this to see what effect it has. The plane is a 35% Carden Cap, about 27 pounds rtf. I fly a mixture of low and high speeds, so it is possible to fly almost 30 minutes with a 32 ounce tank.

Swat Cop

My Feedback: (11)

The bottom fins should be totally blocked off on your baffling. Using this method will dramatically reduce your cylinder head temp. Here is the link in the Cactus Aviation site on how to do it. I used this same method with great results.

http://www.cactusaviation.com/Tech/baffling.html

HP^Matt

Good form Swat Cop, excellent information!


ME

DMcQuinn

My Feedback: (13)

Here are some pictures of my baffling setup. You can see that I have a pretty good fit at the top of the cylinders. But the bottom baffles do not meet up to the bottom of the fins and there is a lot of room for air to flow through this gap, over the mufflers (but not the fins) and out the bottom.

HP^Matt

The bottom baffels are the most important ones, If you follow the information that SwatCop listed from Cactus you'll have a much cooler running engine.
Let us know how it turns out.

ME

Swat Cop

My Feedback: (11)

Here are some pics of the baffles in my 40% Carden Cap 232 / 3W 150. After installing the baffles my cylinder head temp is between 180-200.

DMcQuinn

My Feedback: (13)

Re-did my lower baffles. Much better now. May not have a flight report until a week or so.

Swat Cop

My Feedback: (11)

That should do the trick.

RTK

My Feedback: (1)

DM- Your baffling now looks much better, be sure and have a lot of exit area for the hot expanded air to leave thru.

Here is a thread for you who would like to read about engine temperature misconceptions.

http://www.rcuniverse.com/forum/m_96.../tm.htm#964307

HP^Matt

Yepp, that looks like what ya need. Should help a bunch!

ME

DMcQuinn

My Feedback: (13)

Here's an update: I received my DA ignition and swapped out the original (suspect) 3W ignition. Engine fired right up and I flew today 4 complete flights with no problems. Every flight was at least 20 minutes. So I am cautiously optimistic that the ignition unit (the old one) has a heat-related intermittent problem. I still can only get about 5700 rpm with a 27x10 3W wood prop.