Rotax 503 engine trouble

[skyfox1]

My 503 has a flat spot or you could call it a miss at 3000 rpm soon as you increace throttle once passed 3100 rpm it is fine changed carbys no difference has anyone got any sugestions to fix the problem .

 

cheers Geoff..

 

 

[fly_tornado]

cleaned the carbies?

 

 

[skyfox1]

cleaned the carbies?

The carbys are brand new and clean

 

 

[fly_tornado]

checked for air leaks? fuel lines?

 

 

[eastmeg2]

Check the exhaust system too, since these 2 strokes need the exhaust to have all the right resonances to run smoothly & make power. Could be something as simple as a broken exhaust spring.

 

 

[skyfox1]

Thanks found the problem both cylinder have grabbed ,

 

back to another rebuild.

 

cheers

 

 

[pudestcon]

Have you worked out what caused the problem skyfox1?

 

Cold seizure, lean fuel mix?

 

Pud

 

 

[skyfox1]

Have you worked out what caused the problem skyfox1?Cold seizure, lean fuel mix?

Pud

Hi Pud l think it was running to lean hard to say it grabbed at 3000 rpm well thats wereit was when the engine stop at ,the plugs are nice tan color .

The only thing different has been l changed to castrol active 2t from penrite hi per.

 

The motor runs to full power the only problem l had a flat spot at 3000 rpm.

 

Its now all pulled apart im going to put a set of standard barrels and pistons in it to get back in the air..

 

 

[pudestcon]

Hi Pud l think it was running to lean hard to say it grabbed at 3000 rpm well thats wereit was when the engine stop at ,the plugs are nice tan color .The only thing different has been l changed to castrol active 2t from penrite hi per.

The motor runs to full power the only problem l had a flat spot at 3000 rpm.

 

Its now all pulled apart im going to put a set of standard barrels and pistons in it to get back in the air..

I use Castrol Active 2T and reckon it's an excellent oil. Tell me though; After just changing to Active 2T and having the engine nip up, will you continue to use Active 2T?

Pud

 

 

[farri]

The only thing different has been l changed to castrol active 2t from penrite hi per..

I installed my current 503 DCDI three years ago! It`s done 245 hrs, and for the first 220 hrs, I used Castrol 2T.

 

I asked the Castrol supplier what the difference between the two oils was and he told me that they were basically the same except that Active 2T created less smoke.

 

I decided to change to Castrol Active 2T but I havn`t noticed any difference...I serviced the engine 3 weeks ago, took the exhaust off to check the pistons and rings and found them completely normal... The engine continues to run beautifully.

 

Fuel oil ratio: 50:1 = 40o mls of oil to 20 lts of fuel...I`m using the standard carby jets that come with the motor and use unleaded fuel... I burn 14/15 lts phr.

 

Unlikely to be the Castrol 2T....It`s more likely that your engine was running too lean.

 

Frank.

 

Ps, My engine is inverted! Spark plugs on the bottom.

 

 

[fly_tornado]

check for a fuel blockage, one of my Tornados wasn't running right turned out to be the fuel line was clogged @ the tap on the tank.

 

 

[skyfox1]

Hi Pud yes l will keep using castrol active 2t ,l put new needles and jets in the carbys an hr before the grab they are standed rotax specs for sea level and the same as the ones l took out l re syn the carbys also fuel lines are free and clear no restrictions mine is inverted also farri on my maxair .

 

When l pull the motor apart the crank and pistons have a nice coating of oil over them so dont know why for sure it grabbed..

 

 

[fly_tornado]

there is a good article in experimenter about detonation

 

 

[skyfox1]

Hi FT do you have a link

 

 

[fly_tornado]

http://www.eaa.org/experimenter/

 

http://www.eaa.org/experimenter/articles/2012-01_detonation.asp

 

 

[pudestcon]

Hi Pud yes l will keep using castrol active 2t ,l put new needles and jets in the carbys an hr before the grab they are standed rotax specs for sea level and the same as the ones l took out l re syn the carbys also fuel lines are free and clear no restrictions mine is inverted also farri on my maxair .When l pull the motor apart the crank and pistons have a nice coating of oil over them so dont know why for sure it grabbed..

Hmmm, brings me back to thinking about a cold seizure. Not sure how much correct lubrication mixtures play in a cold seizure scenario. Anyone know?

On a side issue skyfox1, what did you use to sync your carbies? I've just this minute come back from purchasing enough clear tube to make a manometer to sync my carbies.

 

Pud

 

 

[skyfox1]

Pud l used a Syschrometer carby flow meter l bought it from UK it was $60 works great .

 

 

[skyfox1]

http://www.eaa.org/experimenter/http://www.eaa.org/experimenter/articles/2012-01_detonation.asp

Thanks FT great reading learnt alot

cheers Geoff..

 

 

[flyerme]

A cold seizure can occur if an engine is run at full power before it is fully warm, the piston then expands faster than the cylinder leading to the seizure.

 

cold Seizures explained

 

The text below is reproduced from a posting to the BMAA eGroup, where a member helpfully shared this information - which comes from a Rotax expert.

 

First.. the term "cold seizure" is a bit of a misnomer. All seizures are caused by heat/friction. A cold seizure is where the piston expands faster than the bore it is traveling in and contacts the sides of that bore. These are also known as four corner seizures.

 

The worst case scenario is that the engine can just lose power and stop. In the case of a mild (mini) seizure the engine may just lose power for a second or two, but will respond to throttle inputs and will recover when the throttle is advanced. This may happen a few times before a major seizure occurs.

 

Cold seizures "usually" occur after a full throttle run when the engine is powered back to a cruise throttle setting. If the engine has experienced some previous mini seizures, the stoppage can occur anytime in flight as there is already some aluminum (off the piston) attached to the cylinder wall and galling (unwanted removal of aluminum from the piston to the cylinder wall) will be occurring at a variable rate.

 

In a cold seizure scenario the engine may just sputter and lose rpm for a second or two, or it may bring the engine to a complete stop. Once the engine has cooled down a bit it will appear to re-start and run properly. Don't let this fool you. More than one person has tried to fly his plane out of a field where they had to land because the engine quit, only to have the engine fail again in short order.. unfortunately, the second failure usually happens when the pilot has fewer options for a safe off field landing.

 

Don't let "get home itis" bite you.

 

Find out why the engine stopped before you carry on.. After all, the "self fixing engine" has not yet been invented.

 

The cause of the cold seizure can be variable.

 

One obvious one, would be a lack of warm up prior to going to full throttle. Also, long extended descents at low power settings followed by a high power run (go around) can also contribute/cause the problem.

 

A major cold seizure (complete stoppage of the engine) can occur as a result of multiple mini seizures finally causing a big time stoppage of the engine.

 

An easy check for a four corner seizure (cold seizure) on an air cooled engine is to remove the exhaust "Y" pipe (manifold) and take a peek at the sides of the pistons.

 

If the engine has experienced a seizure, the pistons will tell you the story.

 

On a Rotax 582 liquid cooled engine a cold seizure is not usually visible through the exhaust port, and you can not see the piston on the intake port side. You can see a seizure cause by lack of lubrication from the exhaust port.

 

On a cold seizure, there will be vertical scuffing towards to outside edges of the piston as viewed through the exhaust port.

 

There will be two corresponding vertical scuffs on the intake side, but these cannot be viewed without removing the cylinders.. If the engine has experienced a cold seizure these marks will be visible through the exhaust ports.

 

If you have any thoughts that your engine might have experienced a mini through a full seizure, its far cheaper to fix the engine problem than fix both an engine and airframe problem because the engine failed again. The "through the exhaust port" test is simple and definitive!

 

Rotax radiators and thermostats

 

 

Cold seizure on Rotax 582 intake side

 

Cold seizure on exhaust side, the only thing that will be seen is the small mark near the center of the piston the outside marks will not be visible.

 

PTO piston has seizure and varnish down below each ring end gap, plus indication of cold seizure on exhaust side of piston.

 

NOTE, that seizure was not viewable via "thru the port inspection", with exception of aluminum deposits on carb side of liner, which would be viewable externally upon close inspection.