Orange on 582 piston crown

[Brodstol 41]

Hey all,

After moving my jet needle a notch higher in response to the outside temp getting higher, I decided to pull the plugs and inspect with just about 2 hrs after making the change. I noticed a slight orange tint on the spark plug ground electrode. I then looked inside the hole and on top of the piston I could see orange on the piston crown. Temps have been normal with water temps ranging from 170-180 degrees and egt's around the 1150-1175 range. I was wondering what could cause the orange and I came upon this article https://www.aviatorshotline.com/content/detonation-two-stroke-engines stating that the orange is due to detonation and it's a by product of the 2 stroke oil additives getting too hot. The only thing I can think of is the gas I got at the non-ethanol pumps I go to all the time had a lower octane than 92 premium.

I got the borescope out and inspected the piston along with the cylinder walls. See the pics below. I could see no wall scuffing and the piston looks intact with no cracks, melting, or any damage. I then took the y pipe off and inspected more. I could see no apparent damage and the rings move with the piston.

So my plan is to drain the fuel, fill up with 100LL premixed 50:1, install new plugs and then fly above my airport for 30-40 minutes at a safe altitude. Then I'll pull plugs and reinspect.

Let me know what you all think and if you have any insight or suggestions.

 

[Allen Sutphin 705]

From the plug indications you are running too lean, at least any RPM above idle. The idle ring looks good, the mid range seems ok to lean and 3/4 and above looks to lean. And yes you can tell all three stages from the plug.

[Brodstol 41]

Yeah I agree, it just baffles me cause last I flew in 65 degree weather @ 3000ft and have stock jetting outside of a slightly richer needle jet @ 2.74. Also looking at temps throughout the flight I know I never broke 1200 egts. I could be wrong and hopefully going back down a clip on the jet needle will richen things up on the top end. Gonna give a good look over tomorrow and then go from there. Hopefully I just dodged a bullet and no harm no foul on the lean/detonation condition.

 

[1avidflyer 1983]

One thing, is gauges can lie or at least not give an accurate reading.  Plugs say what they see.  And on that topic,  Allen, never heard of reading all three stages at once from the plug.  Please elaborate.  Not doubting you, just wanting to learn some more about it.  Thanks,  JImChuk

[TJay 1041]

I have also seen that with cheap two stroke oils never with Amsoil.

[Av8r_Sed 82]

You’re using the right fuel. Running 100LL will quickly result in lead deposits on the piston crown, rings and plug electrode. It’s OK on  cross country, but I would avoid a steady diet of it. I’d agree with the other comments. Too lean, too hot. Something is causing an incorrect EGT measurement. 

[tcj 150]

Raising the needle would richen the mid range.  The photos clearly show it is too lean.  Are you sure you raised the needle?  if you raised the clip instead of the needle it could cause the lean condition.

Edited 5 May 2020 by tcj

[akflyer 1427]

Raising the needle would richen the mid range.  The photos clearly show it is too lean.  Are you sure you raised the needle?  if you raised the clip instead of the needle it could cause the lean condition.

I agree with Tom.  If you put the clip up one you leaned out the mid range.  EGT's show a trend not an absolute, the plugs say you running lean.  EGT's can spike pretty quick if you hit a thermal or a bump and you unload the engine.  I like to keep mine closer to 105 on my gauge and that seems to keep the plugs happy as well.

 

[Brodstol 41]

I made the needle jet change because I felt like I was too rich especially since it's getting warmer out but obviously raising the clip/lowering the needle just one notch got it in a lean condition. I made the changes back to where it was and will take a flight later this afternoon. Thanks all for the feedback.

[Brodstol 41]

Flew for a half an hour, EGTS rarely if ever peaked over 1100 through all cruise RPMS at level flight, OAT was 70 degrees. The plugs were more brown and the orange is fading away from the piston crown. I'll continue to go a tad richer with the needle jet going up from 2.74 to 2.76 just to be safe.

[Allen Sutphin 705]

Starting to sound better, maybe put a hour or so on it to make sure everything stabilizes and remains close to this. Would hurt anything to go richer but be prepared to return to the 2.74 jet.  1100 EGT is in the ballpark. Fuel also has an effect on EGT's. 87 OCT runs a little hotter than 91 or 93 OCT. Never ran 100LL in a 2 stroke so don't know about it but it would surprise you to find out the OCT rating when using the auto-fuel formula.