Hole burnt in Piston??

[Smiley]

I was flying Saturday after the "Sprinbucks" good game very fustrated! Suddenly a big bang and then an engine out occured. I managed to make a safe landing and safed my plane. A hole burnt in my one piston!

Questions:
1) What is the correct jetting sizes for main & idle jet and needle specs? I'm East Rand based.
2) What else could cause this to happen?

Saturday there was a massive jump in QNH. It was about 1035+. In Heidelberg were this happened ground is about 5000ft. Main jet:150. Was the jets maybe to small to cope with that sudden rise in QNH at that altitude??

Please help with any opinions and technical knowledge!!
Thanks.

[Aviation Engines]

I assume that the engine is a 503. Is it a Dual Ignition or an old points ignition type?

If it is Dual Ignition:
Jet Needle 11K2 Circlip position #2 (from top)
Needle Jet 2,72
Main Jet 150 on the highveld

A hole in the piston a caused from detonation, which is quite often a progressive thing until as in your case, the piston can no longer handle the knocking.

Possibel causes - lean fuel mixture
Low octane fuel
Poor quality of fuel

Regards
Niren Chotoki
Aviation Engines & Acc

[Waldo]

I’ve flown 200h plus on the highveld with 503 dual ignition with 158 Main Jet (engine time = 460 h in perfect condition) – My opinion is that under full power the 158 main jet can reduce this problem as the piston is cooler than with the 150 Main Jet. I will only change to the 150 Main jet above 7500 ft – But then, it’s only me.

[Marc]

Hey Smiley,

I also fly a 503 out of Panorama. About 4 yrs ago, the same thing happened to me.

My jets and needles were set correctly (according to aviation engines and everyone else I spoke to.). The engine was running perfectly for 200 hrs before this.

I was taking off at solitude when the engine started running very rough and lost power. Luckily landed on a road, no problem (except a very broken 503!).

I took the aircraft to aviation engines to try find out what happened, and although nothing concrete was found, - it was suggested that possibly a piece of dirt got stuck in the main jet, causing the one cylinder to run lean (the other cylinder showed no signs of hot running), and therefore too hot.

I don't believe that there was anything wrong with the engine - I was just unlucky. ALTHOUGH, after this incident, I immediately installed a dual EGT gauge! Possibly, the problem could have been spotted much earlier, before it got expensive! ie. One hot cylinder.

Trikes are flown by feel, not instruments. I believe personally that the engine monitoring instruments are far more important than the flying instruments on a Trike.

How was the plane after the engine out?

Regards

Marc Gregson

[RudiGreyling]

Hi Guys,

If it was a jetting problem won't both piston have evidence of running lean?

The Rotax Manual and Recommendation is very clear on the Altitude correction factor. Looks like people are not following the recommendation and still fly with Sea Level Jets at the high veld.

Why is there then a altitude correction table available then?
Any negatives for running it with Sea Level Jets at the highveld?

Are these motors so sensative that even with the correct altitude jetting, a jump in QNH will burn a hole in the piston?

Jislaaik I don't hope so!!!

Here's a link with all the jetting info:
http://www.ultralightnews.com/enginemai ... ngjet.html

Kind Regards
Rudi

[Waldo]

The only negative I noticed is a slightly higher fuel burn at the upper rpm range. Maybe more carbon built-up as a result of cooler combustion temperature and more two-stroke oil – but this I did not notice.

I know of at least 5 503’s that burnt a hole in the piston and all were using the 150 main jet on the highveld.

Kind Regards

[Smiley]

Hello guys,

I must be honest, I'm still not sure what the main jetting size should be!
Rudi is right, according to Rotax manuals the jet to use is definitely a 150. The problem is in practice alot off people are convinced the 158 jet is the safe one and that high QNH can affect sparkplug detination and your plug actually "explodes" on firing which slowly burns the hole.

As was mentioned, a dirty main jet can also cause the piston to run lean. This weekend I will check-up on that and see if my main jet isn't maybe a bit dirty.

For my own peace of mind I bought 158 jets and will fly with those in future.

Any comments??

[lamercyfly]

Fit an EGT guys. Then set your engine to run at about 550 to 580 deg C on both main jets and needle jets.

On a low pressure day, she'll run at about 550, and on a high pressure day, you can expect about 580 to 600 deg. C

Remember that a 2 stroke motor likes to run hot, so running 158 jets is definately not the answer. Loss of power (lots of it) and lots of carbon built up leading to sticking rings and bad wear of the cylinder walls and loss of compression etc.,

A short term solution would be to run 155 jets, but 158's I would say "no ways". I do not even run 158's at the coast. I run 155's on my Rotax 503's, and drop my needle down to the top groove. I have Dual EGT and CHT's on all my trikes, and using the above settings, our engines never exceed the stated temps. 3 of our trikes are over 800hours. So, running 158's in Joburg can only mean you are running seriously rich.............Not good.

But burning holes through pistons, hey man, that is also not good:)

David