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I've been fighting a problem that is still baffling me, and I hope others have had / solved this issue. I throw myself at the mercy of the group to save me from the inferno!
The Airplane:
At present (all previous cowl/baffle history notwithstanding and no longer applicable)...
I have a stock 1940 closed nose cowl. I HAD a stock lower cowl with the very small lip. When the problems started I added a 3" wide hinged movable lip on the back of the stock bottom cowl (Po' Boy cowl flap), with a push-pull cable in the cockpit.
I have a properly sealed, well repaired, refurbished and pretty darn good set of stock Taylorcraft cooling baffles.
The seals against the cowl are way better than most.
The Reynolds Aviation STC has been installed (crumpled aluminum foil to fill large gaps in the baffling against the engine). There are no enormous holes.
The hoses on the intake tubes from the carb spider to the cylinders are average. Small cracks, no huge holes. I reinstalled them with a little Lubriplate grease, so they should be reasonably well sealed.
The engine runs just like a little A-65 should, all things considered. None of the spark plugs are white-hot or burned out. It makes plenty of power and runs smoothly.
The mag timing was recently set to the correct value. It is not advanced.
I installed a four probe Westach CHT, brand new and TSO'd, with a four position selector switch. The leads are spark-plug-washer type, not bayonet.
I boiled the one suspect CHT probe in water... after installation on the airplane... and read 210F on the gauge.
I installed thermax brand color change thermometer "dots" at six places on the cylinder head to verify the surface temps.
I even built a little fairing around the exhaust pipe to prevent high pressure air from coming in the cowl from below and opposing the cooling flow. This fairing would actually try to pull air out of the cowl, helping the flow.
The Problem:
On a full power takeoff, the #1 cylinder CHT climbs immediately to 450F by the time I am downwind abeam of the tower (less than a minute after starting the takeoff. CHT before takeoff (after taxi and runup) is 300F to 325F.
The other day I was having some spark plug problems and did a long runup, two or three times longer than normal. On takeoff, the CHT on #1 cyl. jumped to 475F by the departure end of the runway. I had to reduce power and limp around the pattern at 500 feet and land. The CHT came down normally on final.
The OTHER three cylinders run 40 to 60 degrees cooler across the board.
The stick on temperature dots reveal that the hottest part of the cylinder (between the lower spark plug and the exhaust valve) turns the color of a 435F dot black, meaning that the surface temp. at that location gets above 435. The other temperature dots at other locations show varying cooler temps as would be expected. The intake side fins do not get up to 340F to turn the color of the lowest temperature dot.
The Po' Boy cowl flap does not help more than a few degrees. It is marginally effective under all conditions, almost not enough to read on the gauge.
OIL temperatures are normal. On takeoff they run 140 to 170F depending on OAT. After a 10 or 15 minute climb at 75 or 80% throttle the oil temp will come up to 200 or 205F... I am fairly happy with the oil temps.
The Brain Twister:
On a new design airplane, I would just assume the cowling inlet and outlet areas are out of whack. I'd assume it was a poor design and just saw/poke/bend/twist the cowling until I got more airflow OUT of the cowl and more air through the number 1 cylinder. But Taylorcrafts have been flying for a while on this same cowl design. I also don't want to hack up a cowling unless it is needed. Under any other circumstance I would put louvers or a reverse scoop in the cowl near the hot cylinder and pull more air out where it was needed. But I haven't seen or heard of anyone else having the same problem as I'm having.
Has anyone else had this problem with one cylinder running REALLY hot? I know that the book says an A-65 cylinder redlines at 525F. I have pulled the plug LONG before it ever got that hot. That's just too damn hot no matter what the book says.
So... anyone here have relevant experience with CHT's and hot-running T-crafts that might reveal the cause of this problem? Several people said that an intake tube leak would make one cylinder run hot... but the spark plug is the same color as the others.
The Airplane:
At present (all previous cowl/baffle history notwithstanding and no longer applicable)...
I have a stock 1940 closed nose cowl. I HAD a stock lower cowl with the very small lip. When the problems started I added a 3" wide hinged movable lip on the back of the stock bottom cowl (Po' Boy cowl flap), with a push-pull cable in the cockpit.
I have a properly sealed, well repaired, refurbished and pretty darn good set of stock Taylorcraft cooling baffles.
The seals against the cowl are way better than most.
The Reynolds Aviation STC has been installed (crumpled aluminum foil to fill large gaps in the baffling against the engine). There are no enormous holes.
The hoses on the intake tubes from the carb spider to the cylinders are average. Small cracks, no huge holes. I reinstalled them with a little Lubriplate grease, so they should be reasonably well sealed.
The engine runs just like a little A-65 should, all things considered. None of the spark plugs are white-hot or burned out. It makes plenty of power and runs smoothly.
The mag timing was recently set to the correct value. It is not advanced.
I installed a four probe Westach CHT, brand new and TSO'd, with a four position selector switch. The leads are spark-plug-washer type, not bayonet.
I boiled the one suspect CHT probe in water... after installation on the airplane... and read 210F on the gauge.
I installed thermax brand color change thermometer "dots" at six places on the cylinder head to verify the surface temps.
I even built a little fairing around the exhaust pipe to prevent high pressure air from coming in the cowl from below and opposing the cooling flow. This fairing would actually try to pull air out of the cowl, helping the flow.
The Problem:
On a full power takeoff, the #1 cylinder CHT climbs immediately to 450F by the time I am downwind abeam of the tower (less than a minute after starting the takeoff. CHT before takeoff (after taxi and runup) is 300F to 325F.
The other day I was having some spark plug problems and did a long runup, two or three times longer than normal. On takeoff, the CHT on #1 cyl. jumped to 475F by the departure end of the runway. I had to reduce power and limp around the pattern at 500 feet and land. The CHT came down normally on final.
The OTHER three cylinders run 40 to 60 degrees cooler across the board.
The stick on temperature dots reveal that the hottest part of the cylinder (between the lower spark plug and the exhaust valve) turns the color of a 435F dot black, meaning that the surface temp. at that location gets above 435. The other temperature dots at other locations show varying cooler temps as would be expected. The intake side fins do not get up to 340F to turn the color of the lowest temperature dot.
The Po' Boy cowl flap does not help more than a few degrees. It is marginally effective under all conditions, almost not enough to read on the gauge.
OIL temperatures are normal. On takeoff they run 140 to 170F depending on OAT. After a 10 or 15 minute climb at 75 or 80% throttle the oil temp will come up to 200 or 205F... I am fairly happy with the oil temps.
The Brain Twister:
On a new design airplane, I would just assume the cowling inlet and outlet areas are out of whack. I'd assume it was a poor design and just saw/poke/bend/twist the cowling until I got more airflow OUT of the cowl and more air through the number 1 cylinder. But Taylorcrafts have been flying for a while on this same cowl design. I also don't want to hack up a cowling unless it is needed. Under any other circumstance I would put louvers or a reverse scoop in the cowl near the hot cylinder and pull more air out where it was needed. But I haven't seen or heard of anyone else having the same problem as I'm having.
Has anyone else had this problem with one cylinder running REALLY hot? I know that the book says an A-65 cylinder redlines at 525F. I have pulled the plug LONG before it ever got that hot. That's just too damn hot no matter what the book says.
So... anyone here have relevant experience with CHT's and hot-running T-crafts that might reveal the cause of this problem? Several people said that an intake tube leak would make one cylinder run hot... but the spark plug is the same color as the others.
She said she had no idea what CHT was, all she has had for temps for the last 61 years is oil temp. Settles that. Course we have changed a few cylinders along the way : Just for cheap information, O.T.
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