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Ever since I installed my engine monitor a few years ago, I noticed #2 was running hotter CHT and EGT than the other cylinders (O-540, PA-28-235). I wouldn't have noticed it before, since only #6 was instrumented.
The O-540 in a 235 has a reputation for having a hot #2 CHT, but why the EGT was also elevated was a mystery. It was only 10-20 degrees hotter (CHT) most of the time.
The flexible baffles
on the 235 are attached to the cowl (bad idea Piper abandoned later), and a real pain to change. They are rough, but still intact.
We looked every time the cowl was off to make sure there were no obstructions to the airflow, nothing seen. We made sure the intake runner was not leaking, didn't find any evidence of it. Valves looked good when borescoped every annual while the spark plugs were out.
After the annual this year, #2 was running almost 50 degrees hotter. My first thought was the baffles had finally given out, the cowl off/on cycle for the annual had been their last. So I told my A/P, and he ordered new baffle material to replace them.
While I had the cowl off to measure the material, I decided to take one last look around #2 to make sure something hadn't fallen between it and #4 and was blocking the airflow. I looked very closely this time, and found what is probably the problem. The attached picture is the rear exhaust stud for #2. It is almost impossible to see. To see it, your eyes have to be at one particular spot relative to the engine, and a light has to be either behind (as this case) or in the same viewing angle as your eyes (difficult!).
If it wasn't for the engine monitor, and for my continued search for the cause of what appeared to be a 'standard' problem, this would have gotten a lot worse before it got better. At this point, we should be able to remove #2, get the studs replaced and the exhaust port cleaned up/machined, put it back on and be good to go. Another 50-100 hours, and I'd probably be looking at a new cylinder. Not to mention the risk of Carbon Monoxide in the cabin. That isn't a huge risk in Florida, the vents are all wide open all year long, but still a risk.
The usual signs of an exhaust leak weren't there - no Co2 alarm (have an good electronic one less than 6 months old in the cockpit), no white residue under the cowl, spark plugs all looked consistent with the rest.
From the amount of erosion on that stud, it's possible it was never tightened properly (or maybe overtightened) when the engine was overhauled about 300 hours ago. It's been through 20+ annuals, with at least 4 different A/P, IA's since then, so this is not a slam against my A/P. This stud is almost impossible to see, and unless you are looking intently at just the right place, you'd never see it. It is also likely in my opinion that it just 'dropped' recently. The erosion is primarily where the stud would be when fully inserted the case, so the leakage was primarily there.
In any case, even a small amount of 1500+ degree air next to the cylinder probably explains why both the EGT and CHT were elevated.
Don't ignore the small signs, even if there is a common 'reason' for them. They seldom get better on their own, and it is much better to find them on the ground!
The O-540 in a 235 has a reputation for having a hot #2 CHT, but why the EGT was also elevated was a mystery. It was only 10-20 degrees hotter (CHT) most of the time.
The flexible baffles
We looked every time the cowl was off to make sure there were no obstructions to the airflow, nothing seen. We made sure the intake runner was not leaking, didn't find any evidence of it. Valves looked good when borescoped every annual while the spark plugs were out.
After the annual this year, #2 was running almost 50 degrees hotter. My first thought was the baffles had finally given out, the cowl off/on cycle for the annual had been their last. So I told my A/P, and he ordered new baffle material to replace them.
While I had the cowl off to measure the material, I decided to take one last look around #2 to make sure something hadn't fallen between it and #4 and was blocking the airflow. I looked very closely this time, and found what is probably the problem. The attached picture is the rear exhaust stud for #2. It is almost impossible to see. To see it, your eyes have to be at one particular spot relative to the engine, and a light has to be either behind (as this case) or in the same viewing angle as your eyes (difficult!).
If it wasn't for the engine monitor, and for my continued search for the cause of what appeared to be a 'standard' problem, this would have gotten a lot worse before it got better. At this point, we should be able to remove #2, get the studs replaced and the exhaust port cleaned up/machined, put it back on and be good to go. Another 50-100 hours, and I'd probably be looking at a new cylinder. Not to mention the risk of Carbon Monoxide in the cabin. That isn't a huge risk in Florida, the vents are all wide open all year long, but still a risk.
The usual signs of an exhaust leak weren't there - no Co2 alarm (have an good electronic one less than 6 months old in the cockpit), no white residue under the cowl, spark plugs all looked consistent with the rest.
From the amount of erosion on that stud, it's possible it was never tightened properly (or maybe overtightened) when the engine was overhauled about 300 hours ago. It's been through 20+ annuals, with at least 4 different A/P, IA's since then, so this is not a slam against my A/P. This stud is almost impossible to see, and unless you are looking intently at just the right place, you'd never see it. It is also likely in my opinion that it just 'dropped' recently. The erosion is primarily where the stud would be when fully inserted the case, so the leakage was primarily there.
In any case, even a small amount of 1500+ degree air next to the cylinder probably explains why both the EGT and CHT were elevated.
Don't ignore the small signs, even if there is a common 'reason' for them. They seldom get better on their own, and it is much better to find them on the ground!
