Rotax 618, need help

[BJJOHNSON]

I fly a sportcopter vortex with a 618 engine on it. Here's my problem;

Recently, when taking off I noticed/felt power reduction just at the point of rotation. At first I thought that I had hit something so I aborted and went to check things out. I didn't find anything wrong, so I went back to see if I could somehow charterize what was going on.

The second attempt was the same as the first, at the instance of rotation the engine started to lose power as if it was flooding. Again I aborted and went back to the hanger.

Since then I have changed the spark plugs, rebuilt both carbs, replaced the fuel pump and fuel filter, and replaced all fuel lines. After all of that, this past weekend I went out to fly. I flew several circuits in the pattern with each one ending with a full stop landing. Everything appeared to be OK. I taxied back to the hanger to see if everything looked OK. It did, so I decided to go back out. My intentions was to fly to the north practice area but that was not to be. As I started my takeoff run everthing was just fine, as I reached the correct RRPM and forward speed just as I was getting lite on the mains the engine bogged down again.

I need help, from what I can tell none of the fixes I performed made any difference. Why the engine ran OK at first is a mistery but I'm convinced that my original problem is still there.

Any help would be appreciated.

Basil

[richardkennedy]

Basil, you said "started to lose power as if it was flooding". If it was indeed flooding, did you check the carb floats to make sure they didn't have a hole in them that would allow them to sink in the bowl? Even though you did all the carb work and other fuel related items, maybe it's still starving for fuel. You could put a squeeze bulb on a bypass line and when it starts bogging down give it some more fuel. If it's starving, it will start running better and eliminate electrical as part of the problem. If it runs even worse maybe you are flooding it. Did you replace the pulse line to the fuel pump? Another possibility might be some air getting in the system and losing the prime to your fuel pump. Good luck.

[Russell]

Basil,

Do you have the boat style squeeze bulb in the fuel line?? I had one loose the check valve.There is one on each end. It did not stop fuel flow but it will restrict flow. I believe Dave DeWinter had one almost stop his motor.
Just an idea Russ :confused:

[Brent_Brown]

R.A.V.E. might be sticking? that motor has a exhaust valve that slides up with higher RPMs if it is not sliding it will not make the power it did.

[Aussie_Paul]

It may be over propped and with the first cold flight ok, but when warm is having trouble getting throught the power band.

Aussie paul.:)

[BJJOHNSON]

Thanks all.

"check the carb floats to make sure they didn't have a hole in them that would allow them to sink in the bowl"

I've looked at the floats and there doesn't appear to be a hole in either one of them but I will check it again when I go back to the airport.

"Do you have the boat style squeeze bulb in the fuel line?? "

Yes. The squeeze bulb is bypassed by another piece of fuel line. How do you check the check valves you mentioned?


"R.A.V.E. might be sticking?"

I looked at both of them and they appear to operate correctly.


"It may be over propped"

I haven't change the pitch on the prop. I didn't mention this before but I have put about 60 hours on this prop setting.

[GyroRon]

Time to pull the exhaust manifold off and have a look in the cylinders for signs of damage. Check the pistons and the rings and the cylinder walls.

[BJJOHNSON]

Ron,

If something is wrong with the guts of the engine wouldn't it be evident at lower rpm? This bogging down occur at about 6000 rpm.

Thanks for the suggestion, at this point I'm willing to look at anything.

By the way, do anyone know where I can get a maintenance manual for the 618 engine?

Basil

[GyroRon]

It is easy to take off the exhaust and have a look inside. Might not be anything, but then again the rings might be carboned up and causing a mild sticking action in the bore of the cylinder... Heck I have no idea, but I WOULD look inside the exhaust just to be sure. Make sure to use a thin tip flat head screwdriver to poke the rings in on their groves to make sure they are free to move in their groves and not stuck from carbon build up.

[Alan Coats]

You can find some Rotax troubleshooting info at

http://www.ultralightnews.com/enginetroublshooting/rotaxtr/trrtx1.htm

They also have maintenace manuals available online.

You can also try http://www.rotax-owner.com/index.htm.

Alan

[scott heger]

Basil, way too little information has been provided. How old is the motor, and how many hours are on the engine? Has any work been done on it internally? Heads need to be decarboned, and rings will stick if not cleaned after a certain amount of engine hours. Have the crank seals been changed? Compression on each cylinder? Since it is a 618, it has some years on it. Give some more history, and we can all help you out.

Scott Heger, Laguna Niguel , CA SportCopter N86SH

[BJJOHNSON]

OK,

I've had my aircraft and engine since 2000, N23933. After 162 hrs (10/2003) I had to have the engine bebuilt. It now have 233 hrs on it.

The engine was rebuilt because ... there is no other way to explain it. Poor preflight, poor construction. Let me explain, the jam nut that links the oil injection to the throttle backed off (I forgot to use loctite). The results was a completely destroyed engine, basically everthing had to be replaced. When this happened I was 1500' agl over mostly open desert.

Since the engine was rebuilt, by Critical Engines here in Tucson, it has run very good.

The engine was running great, in fact for a 2 month strech I flew every day. I'm a early riser so I would be ready at legal daylight every day before work and on the weekends to fly. I have my copter in a hanger at the airport which is only ~15min away.

One morning out of the blue the engine started bogging down and that's where I'm at now.

I've always used 100LL fuel, AV-2 two stroke oil and I always check the fuel (I have never heard of anyone getting bad fuel at Marana). I change my plugs every 25 hours and I keep the air filter oiled. Even after 162 hrs there was no to very little carbon build up. Maybe the AVGAS?

Basil

[BJJOHNSON]

It may be over propped and with the first cold flight ok, but when warm is having trouble getting throught the power band.

Aussie paul.:)

Paul,

Help me understand. Would having trouble getting through the power band cause the engine to lose power, it's very noticable both sound and feel. When I back the power back it runs just fine. Doing a runup don't show the problem because my brakes won't hold much past 4000rpm.

[scott heger]

If it has good idle, it is probably fuel or a compression(ring)problem. I would bet on a compression nproblem if it happened quickly. Take a compression check on each cylinder. With the exhaust manifold removed, you can see if you have a stuck ring normally.

Scott Heger, Laguna Niguel, Ca N86SH

[BJJOHNSON]

Had a chance to really look at the engine this past weekend.







The PTO cylinder is very heavily discolored compared to the Mag side. There isn't that much carbon buildup.

I removed the engine and is taking it to the shop Sat.