CHT - upwards creep on #4, 15F

[A2022]

I am beginning to notice some upwards CHT creep on #4, 15F, so I thought I would do a detailed inspection. what I found was the cylinder baffle had a .125-inch gap at the bottom. I believe it was letting the cylinder cooling air escape. I have 1100 hrs with no adjustment since new. I tightened up the safety wife a couple turns and pulled it in. I also gave the others a turn. there is still a small gap at the edge, but I don't want to mess with silicone to seal it. silicone is messy. hopefully, that is the corrective action.

after it was pulled in....

[A2022]

well, pulling cylinder #4 baffle in did not help much, maybe 3F lower. apparently, my engine is not very sensitive to baffle gaps. I should probably check my CHT temperature sensors to verify they are not drifting, but that is not the normal failure mode, so it is probably not that. I am thinking about some method to increase airflow for cylinder #4. I need another 12F reduction on CHT #4.

today's flight was smokey. the ASOS just changes from 2 to 3 miles visibility, so I took off. when airborne, I don't think I had a mile and a half. I think I passed thru some clouds but hard to tell. pretty much flew by attitude today. for landing, passing over the airport, a Saratoga was announcing taking off in the opposite direction (calm day) and said he would be turning north immediately, but he did not do that by ADSB, I could not see him. I think he was on an IFR plan with a fly runway heading out. I extended and lost sight of the airport. not many flying today. I liked it. a few bumps today, but the RV9 is a good platform for this kind of weather.

I learned when you are flying in min visibility in a mixed IFR / VFR environment, it can get complicated.

[A2022]

ACOC air discourager to possibly lower CHT #4.... I really have no idea if this will work but my thinking is the air has an easier "straight" route thru the ACOC so bend the air towards cylinder #4. this deflector is attached to my ACOC aluminum tube stiffener. it's been on there for 1100+ hrs. oil temp will probably increase but my oil runs cool. it would be nice if it works because I like two-fers.

6061 alum and vibration can cause tabs like that to fatigue, so probably better to have stainless, but this is just a test. I am looking for 12F lower on #4.


















***********

this was a failure. #4 CHT is up 4F and oil temp is up 4F but all the other cylinders were lower. it is blocking airflow to #4. I'll rotate the deflector 90 degrees and make one more test, but not looking good so far. however, it was a very nice day to fly.





************

rotated 90 degrees from previous orientation (didn't get a photo). this was also a failure. #4 was even higher. so, something NOT to do.

[A2022]

decided to bifurcate my under cowl to determine the effects. #4 still high.

OK, I'm going to need to get extreme to fix ole #4.

[A2022]

tried a couple things:

1) added air deflectors at the back wall... no beneficial effects
one of the deflectors was ABS plastic, the other was ABS plastic with 10% glass fiber, they were both fine for this short-term testing.

2) added .063-inch washer to the ACOC to increase air gap......no beneficial effects
will remove the .063-washer and return it to the original position.

I am beginning to believe airflow is not the issue and shifting my focus to the mags. not sure how only one cylinder could be high but I'll swap one mag out. is it worth chasing 15F, I don't know, but it bugs me.










*********

[A2022]

in-flight mag check showed left mag to hold higher CHT on #4 than right mag. so, I may have found the issue with the 15F upwards creep on #4. I'll swap the mag tomorrow with a freshly overhauled mag and see if that corrects the issue. I have an old I-K tech engine monitor that cycles thru the CHTs one by one. nice night to fly. I had the sky to myself.

[A2022]

I swapped the left mag with a new one, but it didn't make ANY difference. still the same 15F delta hotter on CHT #4. so, I've tried modifying the under cowl air flow, and a different mag. what's remaining is the fuel mixture to #4. perhaps my inspection of the fuel/air inlet tube was not good enough and the intake coupling needs to be changed and or the fuel mixture from the carb is slightly different. so, those will be things for the future. I do note that #4 has slightly lower compression. shined the exhaust pipes because these have been so good. nothing done in 1100+ hrs. took some photos from under there because you don't see many from that angle. nice day to be at the hangar.

air filter box and baffling look really good. nothing required since new.

compressions:
1 78
2 78
3 76
4 72