Another bad day

[Safety Officer]

Stay away from old auto fuel and use the proper octane and if you change the needle clip position know what effects it has and remember cold OAT's cause even leaner running conditions.

[FastEddieB]

Yikes!

 

How was that caught?

 

Was the damage limited to that cylinder/piston?

[Safety Officer]

Loss of power and rough running. By the time you have any inkling this has happened it is already too late. Plugs are black and low compression. This was cyl. #2. It was limited to #2 and can be rebuilt.

[FlyingMonkey]

Ker-pow! Ugh.

 

How old and what octane fuel was used?

[FredG]

Since the same fuel went to all cylinders, it is interesting that only one was damaged. Did you get a good look at the others?

[FastEddieB]

Since the same fuel went to all cylinders, it is interesting that only one was damaged.

 

Good point!

 

Post hoc, ergo propter hoc?

[FredG]

Eddie, there you go again, raising the intellectual level of the discussion (this time with Latin)!

But, in a word, yes.

[FlyingMonkey]

Old fuel is automatic if you don't fly much and let the fuel sit in the plane and in the float bowls. Everything dies when a machine sits, batteries, fuel especially.

 

Really it takes about six months or more for auto gas to start getting iffy. If I let a plane sit that long without flying it I'd drain the gas into my car and refill the airplane. So I'm really wondering exactly how old that gasoline was.

 

But you are right, letting an airplane sit is the worst thing for it.

[FastEddieB]

Another option is, if you suspect your MOGAS may have sat too long and dropped below 91 octane, just top off with some 100ll and drag it back up into the acceptable range.

 

Unless you're topped off, of course - then you would have to drain some out first.

 

And the high test around here is 93 octane, so it can slide a bit and still be OK.

[FlyingMonkey]

Another option is, if you suspect your MOGAS may have sat too long and dropped below 91 octane, just top off with some 100ll and drag it back up into the acceptable range.

 

Unless you're topped off, of course - then you would have to drain some out first.

 

And the high test around here is 93 octane, so it can slide a bit and still be OK.

 

If it sits for *too* long, it starts to congeal and form varnish and gum deposits that can clog filters, injectors, or carb jets. I'd do what you say if it's six months or less, after that I'd drain it.

[procharger]

Pistons don't look like they were lean no scars on piston skirts, of course who really knows what happened, I have seen a lot of leaned out pistons,it looks like ring may have broke or top of piston gave up?????????? If none of the other cylinders or plugs look lean something broke.

[Jim]

My humble opinion is that 100LL lead buildup is the problem and stuck the rings in the defective cylinder. That or the owner put some jet fuel in the tank by accident. If I'm right about the lead, all the cylinders need to pulled and the pistons and rings cleaned.

 

Possibly relevant, page 2, http://www.tsb.gc.ca...14/a00o0214.asp

 

 

 

I keep fresh gas in my airplane, but just the same, I'd be hesitant to blame it. I've let my chainsaw sit with old gas for 3 years and it still ran fine on what was in the tank.

[Roger Lee]

Typically detonation happens in one cylinder first. The circumstances are just right to happen in one, but rarely happens in 2 or more at the same time. This looks like a typical detonation problem. I have seen more than 6 from people not following Rotax recommendations and doing their own thing. It is very costly. I talked to the Safety Officer and know one seems to know the cause yet.

 

 

Quote:

Detonation occurs when excessive heat and pressure in the combustion chamber cause the air/fuel mixture to autoignite. This produces multiple flame fronts within the combustion chamber instead of a single flame kernel. When these multiple flames collide, they do so with explosive force that produces a sudden rise in cylinder pressure accompanied by a sharp metallic pinging or knocking noise. The hammer-like shock waves created by detonation subject the head gasket, piston, rings, spark plug and rod bearings to severe overloading.

Mild or occasional detonation can occur in almost any engine and usually causes no harm. But prolonged or heavy detonation can be very damaging. So if you hear knocking or pinging when accelerating or lugging your engine, you probably have a detonation problem.

 

Try a higher octane fuel. The octane rating of a given grade of gasoline is a measure of its detonation resistance. The higher the octane number, the better able the fuel is to resist detonation.

 

"Read" your spark plugs. The wrong heat range plug can cause detonation as well as pre-ignition. If the insulators around the electrodes on your plugs appear yellowish or blistered, they may be too hot for the application.

 

Check for engine overheating. A hot engine is more likely to suffer spark knock than one which runs at normal temperature. Overheating can be caused by a low coolant level, a slipping fan clutch, too small a fan, too hot a thermostat, a bad water pump, or even a missing fan shroud. Poor heat conduction in the head and water jackets can be caused by a buildup of lime deposits or steam pockets (which can result from trapped air pockets).

 

Check for a lean fuel mixture. Rich fuel mixtures resist detonation while lean ones do not. Air leaks in vacuum lines, intake manifold gaskets, carburetor gaskets or the induction plumbing downstream of a fuel injection throttle can all admit extra air into the engine and lean out the fuel mixture. Lean mixtures can also be caused by dirty fuel injectors, carburetor jets clogged with fuel deposits or dirt, a restricted fuel filter or a weak fuel pump.

If the fuel mixture becomes too lean, "lean misfire" may occur as the load on the engine increases. This can cause a hesitation, stumble and/or rough idle problem as well.

The air/fuel ratio can also be affected by changes in altitude. As you go up in elevation, the air becomes less dense.

A carburetor that's calibrated for high altitude flying will run too lean if driven at a lower elevation. Altitude changes are generally not a problem with engines that have electronic feedback carburetors or electronic fuel injection because the oxygen and barometric pressure sensors compensate for changes in air density and fuel ratios.

 

Change your flying habits. Instead of lugging the engine, try less prop pitch.