Detonation Inspection

[RVG8tor]

Okay I am going to get the knuckle head award on this one. I was on my third flight of the day, ( good weather in the NW so I wanted to get as much testing done as possible), The is hour 20 on the engine.

At the end of the flight I decide to do a few touch an go. After the first one on downwind I want to bring the prop back a bit for noise reduction but I am still climbing so I don't touch the throttle which is WOT. I pull but don't hear the usual sound so instinctively I pull more then engine gets rough and backfires.

I pull the throttle back and in doing so I see that instead of the prop I was pulling the mixture back. I shove it to full rich and every thing seems normal. I fly one more pattern and land and no abnormal indications from my engine.

I downloaded my data from the EFIS and the event was just under 30 seconds. My CHT never changed but the EGT went from 1350 to 1495 on the hottest (#1 it reads hotter than the others) The other cylinder EGT maxed out in the 1440-1460 range.

So if I understand things correctly I more than likely had a detonation event, so what do I look for to make sure the engine is okay. Post flight inspection shows nothing abnormal. It is good weather again here today and I want to fly again but I feel like I need to do something more to make sure I did not damage anything. At a minimum I want to look in the spark plug holes, I don't have a bore scope but I have a snake camera. I figure I can see damage to the top of the piston and anything abnormal on the bit of the piston walls that I can see.

So any advice from someone experienced with engines or any recommendations on how to proceed. Any prompt replies are appreciated. Since it would be good to get some hours in on the good weather day we will have today.

I did learn the deluxe throttle quad and flying with gloves on requires a bit more attention to detail when adjusting levers!

[airguy]

I don't read anything in your description that says anything to me other than normal leaning (with too much % power) which puts you in the "red box". This doesn't automatically mean detonation, just that you are in the danger zone. Detonation is characterized by a runaway CHT which you didn't see.

Even a full-on detonation event is not going to trash an engine in a few seconds.

[DEWATSON]

Mike,

You didn't hurt a thing....don't give it another thought.

[schristo@mac.com]

This is a non event...

[49clipper]

You most likely have nothing wrong in your engine. But, if you really need to look, detonation is usually shown around the top edges of the piston. But, it takes a while for that to show. It would look like corossion or eating away at the edge of the piston. For a brief moment of this, you will not see any damage. I see it when I rebuild engines, but they have hundreds of hours on them. These engines can run in light (underline light) detonation for hundreds of hours before anything bad usually happens. it can lead to preignition which of course is detrimental to the engine in mere seconds.
Jim

[RVG8tor]

As usual I am making this out to be more than it needs to be. I will take a look inside and then go fly again. Looking at the data the throttle was back to a normal position with in about 10 seconds but it took 30 seconds for the EGT to peak and come back down.

This is a relief, i was reading about detonation and had convinced myself I must have done this.

Cheers

[RVbySDI]

As has been stated, you made an error that briefly leaned the engine into an area of POTENTIAL DANGER but not necessarily ACTUAL DAMAGE.

Just to clarify a point. One key to understanding the difference: you stated in your description that your CHT's "never changed". Detonation is a cylinder heat issue (CHT) NOT an exhaust gas heat issue (EGT). Watching your EGT's rise drastically for a few seconds then pushing the mixture knob rich when discovered did nothing to your engine of any consequence. When leaning your engine you want to observe the EGT temps while making the big mixture pull (BMP) because of the extremely fast reactionary time of that EGT reading. This allows you to be in control of the event before something gets out of hand. However, if detonation were to occur, it will be the CHT readings that will give it away. Paying attention to the CHT readings is the important observation point for maintaining control over whether you are dancing with disaster with detonation or not.

Live Long and Prosper!
Steve

[DanH]

Another good example of why Lycoming should publish the FAR-required detonation survey results. In the vacuum, we get the Red Box.

Mike, you'll find some of the detonation survey data for the angle valve IO-360 here:

http://www.vansairforce.com/communit...7&postcount=81

Specific to your question, the first chart indicates zero detonation at WOT and 2700 RPM. Two caveats; data was taken with timing at 20 BTDC, and the parallel valve combustion chamber may net a different result.

Obviously I prefer data, but my belief here is like the others....a non-event.

[rv8ch]

Hi Mike,

Totally unrelated to this thread, but I just wanted to send you a short "thanks" for your blog - lots of very useful information on there!

Regards,
Mickey

[JonJay]

I sat with a major fuel component supplier and key sponsor to the often cited and highly regarded engine operation guru's (names omitted on purpose) at Osh a few years ago. He said it was highly unlikely that you could cause detonation on the four cylinder lycomings or clones even if you tried. (Normal configuration properly timed).
I will throw out my challenge again to anyone who can find an example of a detonation event occurring as a result of pilot error. Thus far, none have come forward.
I am not saying we should not be mindful of how we operate our engines or be careless but accidental mixture pulls happen all the time and nobody has hurt anything that I have been aware of. Not saying it has not happened but....