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HelicopterMain Discussion › Hello guys motor question
08-27-2012 11:39 AM  5 years agoPost 1
speilhaupter

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USA East Coast

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I have a question about a burnt up os 91.My muffler line popped off i ran lean. It stalled and the engine itself smoked for a bit. I took the whole engine apart, there was some scoring, and i replaced the sleeve, piston, and piston ring. My question is how much scoring has to be there for the engine not to run? if there is scoring on the piston and inside the sleeve would that cause it not to run. The piston ring kinda looked very gray, and the new one was black. Once the pistion ring goes bad, thats the reason the engine will not run corrcet? no preassure in the engine? can somone help explain this a bit more

my son is my instructor.

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08-27-2012 12:05 PM  5 years agoPost 2
rpat

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Weirton, W. Va.

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First off did you try to start it after it cooled down? Scoring is something that is relevant, it all depends how much scoring happens. If you tried to start it up after it cooled down and it started, then you have to evaluate whether the engine has the same power that it had before the lean run.If the ring is shot, or the cylinder is scored you may get it to start but it will be way down on power because you have lost the compression.

trex 700fbl cal30,minititan,, trx600fbl,trex250,logo 500,Velocity N2

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08-27-2012 12:08 PM  5 years agoPost 3
McKrackin

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Lucasville,Ohio

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It takes some serious damage to keep it from running.

Yours quit because it was so hot the piston expanded and got too tight in the cylinder to run.

It will run with quite a bit of damage..It won't run well!!!

The gray ring was worn out and probably happened fast with the over heated piston pushing it too hard against the sleeve.
It should float and not be pushed into the cylinder wall.

My last incident with the muffler pressure tubing popping off burned a hole in my piston and ruined the sleeve.

If you can feel a scratch in the sleeve,it's ruined. You can't buy over sized pistons and you would have to have one if you honed out the scratch....Just pitch it in the trash in this case.

Some shiny spots on the piston from wear won't hurt a whole lot (the ring makes the seal for compression) but if you can feel the scratch...pitch it.

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08-27-2012 12:56 PM  5 years agoPost 4
airdodger

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Johnston USA

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The compression has a lot to do with the ignition of the mixture and the gas pressure developed upon the firing. The drag from the aluminum being deposited on the liner from the sticking due to the overheating is enormous. As the piston continues going up and down at around 280 times a second, more and more aluminum is deposited and pushes harder against the piston, eventually the power can not overcome the friction, and power is decreasing every stroke on top of that.

The aluminum is being deposited between the ring land and seizes the ring in the piston. That hurts because it is the gas pressure from the combusted mixture that pushes the ring against the liner and seals the gas pressure from leaking. This snowballs because one of the functions of the ring is to transfer the heat to the liner and now it is not in full contact around the liner and can't pass the heat off. The ring is made to float in the piston, sometimes it will break the top ring land off the piston if it catches on the aluminum on the wall..

All the parts need to function properly to produce max power, everything is important. Fit, finish, and clearance have to be maintained. These are small displacement engines so just a small step down on power every stroke means a lot when multiplied 280 a second.

A lot more is going on while this is happening but that will give you some insight of the process.

Chris

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08-27-2012 01:05 PM  5 years agoPost 5
McKrackin

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Lucasville,Ohio

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Exactly right.
But aluminum deposits can be polished off.
A scratch can not.

If you hone out a scratch,you have actually bored out the cylinder and the ring will not seal because the ring gap is too large.

The ring gap is the gap between the two ends of the ring.

He mentioned scoring but a LOT of guys mistake the aluminum deposits for scratches and scoring.

Nice post airdodger...

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08-27-2012 02:01 PM  5 years agoPost 6
speilhaupter

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USA East Coast

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yes tried starting

Yes i tried starting it after it cooled down.It wouldnt even give a hint of turning over. I essential rebuilt the whole engine. I had a bunch of parts laying around, so i even gave it a new crankcase.

It was my fault because the muffler line must have come off the flight before. it sounded off(not corrrect) (pissed off)..i landed and said wtf to myself checked it over but must have missed it...I richened it. I thougt maybee somone at the last even Maybee turned the dials and i was not aware..i took it up again and it sounded whiney, porr litle engine. lol. so now i have to break in the engine again. only had maybe 60 flights on it. if that.

my son is my instructor.

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08-27-2012 02:19 PM  5 years agoPost 7
McKrackin

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Lucasville,Ohio

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Yes i tried starting it after it cooled down.It wouldnt even give a hint of turning over.
This term always messes with me.

Do you mean it was locked up?
Or do you mean it wouldn't start but was turning?

I hear people say that all the time with cars and when I go to help,the starter is cranking the engine like normal but it won't start.

Turning over means the crank is turning....An engine will turn over without starting.

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08-27-2012 03:32 PM  5 years agoPost 8
speilhaupter

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USA East Coast

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motor

the motor was turing over...but it just was not igniting. NO LOCK UP

my son is my instructor.

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08-27-2012 05:02 PM  5 years agoPost 9
rpat

rrElite Veteran

Weirton, W. Va.

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OK you might have fouled the plug when trying to restart the engine. Did you look at the plug after it would not start? Often times the plug will foul up from all of the aluminum floating around and at times it destroys the nichrome filament.

trex 700fbl cal30,minititan,, trx600fbl,trex250,logo 500,Velocity N2

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08-27-2012 07:49 PM  5 years agoPost 10
airdodger

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Johnston USA

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A bunch of what parts? Tell us how you reassembled the engine and the parts you used.

Makes no sense to change the crankcase, how come?

Chris

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