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What happens when.....

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Old 02-22-2011, 11:29 AM
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BillO
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Default What happens when.....

[size=2]Hi Bob,
A friend and I were talking just yesterday just about this. Forgive me if it's too basic a question, but so many people have their own "expert" opinion on it. I just have to ask it here.
What actually when an engine has a lean run? - whether from having the needle in too far and causing the engine to lean too far during flight, or if a foaming issue occurs, etc, it makes no difference, right? A lean run is a lean run caused by what ever, right?
Your glow plug most likely burns out?
I've read that some guys even have the glow plug blow out of the head soemtimes?
The sleeve may roatate somewhat, causing the port to be off of alignment?
The piston and/or sleeve may get discolored?
How is the engine damaged? What actually must be done to fix the engine?
I (so far) have not had a lean run, but my friend has had. He gave the engine away in a plane he sold, telling the buyer so.

Thanks for the reply.
Bill O in still very snowy London, Ontario)
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Old 02-22-2011, 08:04 PM
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Default RE: What happens when.....

A really lean run will cause extra heat that will cause very excessive wear. Real engine damage, not just a blown plug.
It usually leads to a new sleeve and ring at the least.
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Old 02-23-2011, 02:22 PM
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Default RE: What happens when.....

The sleeve will not turn during a lean run. What causes the sleeve to turn is during a lean run the head becomes loose and on the Jett, the head is two piece utilizing a button in which the glow plug is threaded. What happens is that the button turns when a new glow plug is tightened and the button turns the sleeve. If you check the tightness of the head bolts after a lean run, you will not have this problem.
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Old 03-05-2011, 10:48 AM
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Default RE: What happens when.....

bump

Bob, - I hope you're ok, and able to give my post your consideration.
Thanks,
Bill
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Old 03-05-2011, 02:53 PM
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Default RE: What happens when.....

the answers given are pretty correctTH, nz
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Old 03-05-2011, 03:51 PM
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BillO
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Default RE: What happens when.....

BigTrev and the others:
Thank you!
Trev, - I hope you and yours or ok since the quake there. Thanks to all for your inputs. I guess I knew some about that stuff as replied to, and I knew (and know still) about the sleeve rotating issues being mainly from the button. I own 2 of Dub's engines. (a cast SJ50 & a 90LX BSE) and use a proper torque tool for the screws. (no guessing!)
I sometimes know answers of questions posted here by some [8D] , but the RCU stance is that us "non-officia" guys can chime in on the other forum areas, but on the specific engine areas, only certain people are to offically respond, to keep mis-information from getting on here. I know we've all seen the wrong answers at times for the questions on the other engines. Everyone owning a Jett is different! because we own some of the best engines around.
I'd just like to hear the "official" in-depth response that Bob is so famous for. I'm willing to wait for him to get to the forum here. I know life sometimes has its curves for us. The one line answers are a little short of what I am looking for.

The best to everyone.
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Old 03-06-2011, 10:19 AM
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Default RE: What happens when.....

Hi Billo,

Sorry for the delay... I had not seen this post in my email and somehow over looked it. My apologies.

Yes, in general your question was answered by the others.

Lean run means a very high temperature in the combunstion chamber. Fuel burns its hottest. It can and does detonate, rather than burn smoothly, in worst conditions.

One would think you would want this type of mixture Effiecient use of the fuel and air mixture - most possible energy released.

But it creates a condition that tends to get worse than better. It can be uncontrolled. Heat will cause lean to become leaner That temperature can and does approach the point where damage can and does occur to aluminum, and also steel parts. It also causes some lubricants to break down. So this is the biggest risk. You have physical and mechnaical things that go wrong with a lean run.

Most engines can tollerate and surve lean conditions for a period of time. If you throttle back, or shut down fairly quickly .... usually litttle if anything occurs permanently. But if it repeats, or you let it run like that for a while (for instance a poorly installed fuel system and flying it over and over again) the engine will be damaged.

Yes, when overheated, steel bolts can come lose from the AL case. The glow plug often will overheat and burn out the element (blown plug). On a Jett engine, yes, if you are not mindful of this, and change the plug, you can rotate the head button and sleeve when installing a new glow plug. So something to keep in mind.

A good fuel system, and good engine techniquies will prevent 99% of problems.

Bob
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Old 03-06-2011, 11:17 AM
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Default RE: What happens when.....

Very informative, Bob. Many thanks. (and no problems with the wait referred to. Notification systems, to you or anyone can go awry at times.)

Bill
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