Cold seizure?

[Yenn]

I was not at the strip last weekend so missed an engine failure which resulted in an outlanding, with no damage or injury.

 

It seems the pilot was worried that his Rotax 582 engine was not giving full power, so he tied the plane to a tree and did a full power runup to check it. I have seen him do this before.

 

It seems he then waited over an hour before he went flying, did a quick taxi to the end of the runway and took off. A few pilots must have been concerned because the continued to watch him and saw him suddenly descend. A search party went out with the trailer we have for plane transportation and eventually found him about 4km away, in good spirits.

 

The pilot talked to someone at Boonah who said it was probably a cold seizure and the engine has been sent for repair.

 

When I first heard the story I was not told about the delay between the run up tied to the tree and the take off, so didn't consider a cold seizure, but that engine would have been cold.

 

Full power for a short time from cold and then a reduction to cruise seems to be a firm

 

foundation for a cold seizure. I hope I get to have a look at the pistons.

 

 

[Guest J430]

Well Ian, I guess that is a good reason to ensure your engine is at the required temperature before sticking it to it!

 

Glad to hear nothing bent broken or injured!

 

J

 

 

[robinsm]

Hi all,

 

Must be the season for 582 blow ups. Last week I had an efato at 250ft above the local aerodrome. Managed to land safely. Checked the spark plugs and found aluminium on the front spark plugs. Stripped the motor down and found that I had melted a hole in the crown of the front piston of the grey head 582. There was no problem with the rear piston. There was no indication on the gauges of any problems. The scuff marks on the piston show in the upper part of the piston skirt and are equally spaced on each quarter of the piston. No apparent damage to the bore or the head. I had just changed the main jets in the carbys from 165 to 162 in order to bring up the egt,s as they had always read 850 to 900 at cruise. The day was fairly cold, 9-11 degrees, and it was the first flight of the day for me. The fuel had been in the aircraft for about 2 weeks. Anyone have ideas why this occurred. Your input would be greatfully appreciated so I don't do this again.

 

Cheers

 

Maynard

 

 

[kfowler]

maynard are these engine two stroke if was the spark plug the right heat range if you go hotter on the heat range you melt a hole in the top of the piston above the spark plug all the best keith

 

 

[vk3auu]

Robinsm. According to Rotax specs, EGT should be 500 to 620 deg C with 650 C max. Seems like you got the mixture a bit lean if you punched a hole in the piston, so perhaps your gauge is not telling you the truth.

 

David:crying:

 

 

[robinsm]

Sorry Dave, EGT is in degrees F (range is 950 to 1150 I beleive. Sorry for the confusion. Kfowler, plugs are BR8ES as recommended by rotax for this 2 stroke. Thanks.

 

Cheers

 

Maynard

 

 

[vk3auu]

I thought that was the case. The temps seemed impossibly high if it had been centigrade. That makes me think that your gauges are reading low.

 

David

 

 

[Knighty]

Timing

 

Maynard & fellow readers

 

Have a look at the timing on the motor, egt's might read fine however other sinister things can be happening in the combustion chamber we are not aware of. However; I am sceptical if a small error in timing could melt a crown?

 

I cant remember off hand what the specs are and cant lay my hand on them at the moment because I am at work. Rotax engines need to fire X mm or thous before TDC and to do this we place a dial guage into the sparkplug hole to determine piston placement and align the CDI pickups and the triggers on the flywheel by sight. Now here is where the drama starts on the grey engines!!! The pickups are factory set however I have ovaled out the bolt holes on the pickups to make this necessary adjustment, and I might add I've worked on a few 582's experiencing the same problems as mine. You would be surprised how much the timing was out on these engines!!! I THINK that the blue top engines have the triggers already ovaled/elongated to make timing adjustments?

 

I have made my dial guage attachment out of an old spark plug by bashing out the ceramic guts and drilling/silver soldering a nut to attach a grub screw to secure the shaft on the dial guage (bloody rough bush cocky backyard mechanics!!), and works perfect and cost me bugger all.

 

Just to confirm my advice I suggest you to contact a level 2 who is Rotax 2 stroke savy. If you need a hand or the right specs give me a yell and I will post the info on the forum for all to read.

 

Also I would like to add that the engine that has the melted piston will have to have a thorough internal cleaning and thats a big job within itself, no room for rough she'll be right mechanics here!

 

Regards

 

Knighty

 

 

[Captain]

Full power for a short time from cold and then a reduction to cruise seems to be a firm foundation for a cold seizure. I hope I get to have a look at the pistons.

Ian,

 

 

 

I have experienced cold seizures in 2 stroke bike and superkart road racing and I always thought they were characterised by a nip up that was more likely to be on the sides of the pistons due to differential expansion of the piston and barrel, caused by sudden uneven heating most likely due to not enough warm up.

 

 

 

If this piston has holed, I would look first for a fuel (or maybe and icing issue thru that carby) that would make the problem more specific to the one that gave a problem.

 

 

 

On the Rotax's that I have raced, we always ran richer jets on the back cylinder too (but we were reving them to 13000 as well).

 

 

 

Regards Geoff

 

 

[Bruce Robbins]

Hi all,...................... Stripped the motor down and found that I had melted a hole in the crown of the front piston of the grey head 582. ............... Anyone have ideas why this occurred. Your input would be greatfully appreciated so I don't do this again.

Cheers

 

Maynard

Maynard,

 

Have a look on this site for a lot of Rotax info.

 

http://www.800-airwolf.com/articles.htm

 

Cheers,

 

Bruce

 

 

[Knighty]

Ian,On the Rotax's that I have raced, we always ran richer jets on the back cylinder too (but we were reving them to 13000 as well).

 

Regards Geoff

Another comment if I may please.

 

I have experienced the same on a 582 with the rear pot slightly warmer at about 75 degree's F cruise @ 5,800rpm according to the EGT. I managed to adjust this by float / fuel bowl adjustment still in accordance with manufacturers recommendation on carby fuel level. I think Rotax says that if there is more than 25-50? F degrees differnce then one must look into the problem immediately.

 

As for my twin V roadbike engine the rear carb jets are a size larger allowing a richer burn to aid cooling unlike the Harley engine running a single carby.

 

As for the timing on Maynard's beast and the piston melting if it was the timing then both pistons would/should be effected due to the CDI system firing continuously every 180 degrees of engine revolution. As for carby icing on only one carby I doubt, maybe a small bit of crap in the main jet or temporary fuel restriction on that pot going unnoticed for a minute os so at 6000rpm on climb out, especially when in a busy circuit???. I am sure I am guilty of not constantly watching the guages when aviating and especially after takeoff dodging power lines and trees (just using this for an example and to contextualise the subject at hand).

 

Looking forward to hearing the actual cause of that melted crown!!!

 

Knighty

 

 

[robinsm]

Knighty, the investigation continues, I am leaning towards fuel (

 

 

[robinsm]

forget the last, pushed the wrong button,

 

now as I was saying, I am leaning towards fuel problem, as you say, maybe a partially blocked jet, or possibly (not sure how) seperating fuel,? old fuel? etc. When I find out I will let the group know. Help and ideas greatly appreciated.

 

Thanks

 

Maynard

 

 

[Yenn]

Robinsm. Have you thought that the scuffed pistons, may not be the main factor in the engine failure, but is a sign of cold seizure. My guess is that the blown piston crown was probably due to lean mixture, poor fuel or incorrect timing. Timing doesn't alter all that much over time, unlike points ignition in 4 strokes.

 

 

[youngmic]

2c worth.

 

The scuff marks:

 

You stated that they are on equal quarters of the piston skirt, in the world of Lycomings and similar this is an indication of poor differential cooling. What you may be looking at is that the scuff marks correspond with the cylinder base nuts/bolts, and or head bolts this is an area in the circumference of the bore which exhibits more rigidity than the areas between. As the bore dimensions increase with increasing temperature this area is slower to grow and hence represents a closer cylinder bore piston skirt clearance.

 

The hole in the piston:

 

Lean or timing could either or both be a culprit. But essentially what you have is a break down of the cool boundary layer (relatively) of air on the piston crown. The temperatures that occur during the combustion event are of a magnitude much greater than the melting temperature of piston alloy. The only thing that protects and stops melting is the pistons average temperature and that thin but important boundary layer of cool(er) air. What can and does typically break through that layer is a sonic pressure front (flame front) ie. detonation or pre-ignition. Pre-ignition ie. an incandescent spot on the cylinder head or grossly advanced timing will result in very rapid failure < 1min.

 

Detonation is much much slower to destroy an engine and needs to be reasonable severe.

 

Perhaps looking at both your issues in conjunction and history we might see some idea of what happened.

 

You down size the main jet and thus increase the temperature of the combustion event. Now the front cylinder perhaps slightly and inherently leaner now has a reduced detonation margin.

 

I don't know your installation layout but if your front cylinder is cooled by the free stream as opposed to fan cooling perhaps it's possible that the cylinder temps weren't quite there yet and with the application of take off power your pistons are now rapidly heating and thus growing yet the front cylinder being free stream cooled by rather cold temperatures of the day (9'c) doesn't expand as quick as the rear and starts to scuff skirt to cylinder.

 

But so far so good it's still running but now its generating a lot of heat back into to piston (and the cylinder, but piston alloy expands quicker) with the metal to metal contact and that cooler air protecting the piston crown that isn't quite as cool and the mixture that is leaner due to a jet down size, and also the air density which is high due cold OAT thus leaner and the horsepower capability is up due to a leaner mixture and the air density being high and so therefore the heat being produced is up also.

 

Detonation might well be now occurring.

 

If your piston wasn't scuffing you could have perhaps got away with the detonation, or if you had scuffing but no detonation again you might have got away with it, but together it might all just be to much and self compounding.

 

Perhaps the guru's and regular users of these engine might shed some light on whether detonation is an audible event on these engines, it's not on Lycomings and the like. So maybe you don't hear the cry's from your engine.

 

But don't discount a partially bloked jet either.

 

Maybe food for thought.

 

M

 

 

[youngmic]

Oops.

 

Thought about this a little more and realised the 582 is water cooled.

 

So I spoke to my dad about this, he's an outboard mechanic and he pretty much ruled out cold seizure factors.

 

And when I think about it in all the years of abusing 2 strokes from outboards to motocross bikes I've never really seen cold seizure, and the small outboards are a classic for this sought of treatment, start to flat out in 2.8 seconds and it never seems to worry them. Even the big ones used to get little respect, think water skiing and motor off drifting in the middle of the river swapping skiers, refreshing beers, laughing at the last crash, then it's motor on take up slack and flat out till you bend the throttle lever, and under a huge load.

 

What he did point out is mixture and timing, some how I doubt timing was the issue in light of the other factors outlined.

 

As the old man pointed out 2 strokes are critical on mixture as the cooling issues are different to that of a 4 stroke. On a 4 stroke the heat path for piston cooling is via the rings to the bore but on a 2 stroke this is tricky as the bore has much less surface area due to the ports, so the fuel takes over to assist in cooling particularly the swirling cool fuel on the underside of the piston crown. Reduce the amount of cooling fuel and the issue can compound quickly.

 

So perhaps the principal issues as in my previous post but with out the issue of piston bore clearance due cold temps may still be a likely scenario.

 

I can see that the question arises of why just one cylinder failing and not the other, but it's not that unusual, rarely do both cylinders experience the same combustion parameters. And looking over the old mans shoulder over the years as he'd pull down another big bore 2 stroke it was rarely the case that all pistons were damaged, usually just one and perhaps another on it's way.

 

And thinking about it given this whole piston failure event happens quite quickly it's not hard to see that perhaps the other one was suffering but still before the point of visible damage and the failure of the first brought the whole proceedings to a close.

 

Good to see you pulled off the forced landing without to injury.

 

M

 

 

[robinsm]

Thanks for the help everyone. After reading your replies and doing some heavy thinking, I have come to the conclusion that the piston failure was the result of the fuel leaning out. The only change I made was to the main jets. I have a bad habit of trying to improve things when they are obviously going fine as they are. (The xair was going well, the only problem was the EGT readings being low.) Now if I had accepted those readings then I may have been ok. I do not believe the small scuff marks contributed to the failure, I think they are a result of the failure. (cold engine, pre igniting fuel = overheated and expanded piston touching cylinder walls. (as a point of interest, nothing shows on the rear piston or cylinder wall).

 

I think the lesson I have learned from this is that good performance as opposed to perfect performance is acceptable and ... leave the @#!@#*@#!! thing alone, don't fiddle!!!!! Thanks again for the help. This group is great

 

Thanks

 

Maynard

 

 

[BigPete]

The bottom line........