Flying Dave
Active Member
We used aluminum tape on the front cylinders to help with temps. Might be worth a shot to experiment with. YMMV…
Problem solved: High CHT on #3 Cylinder
Snowbirdxx
Well-Known Member
if #4 is running hot in the climb, retard the throttle about 0.1 to 0.2 ichches of MP. Theat heps on my engine to lower the CHT.
TheFlyingMouse
Active Member
My local mechanic was kind enough to work with me to fix my cracked #4 baffle with a doubler. I also siliconed in quite a few air leaks, and we adjusted the front flexible baffles to angle upward against the cowl.
First takeoff seemed to go pretty well. The #4 did not get over 400 until about 1000 feet. Subsequent takeoffs started showing the old behavior of getting to 450. It seems marginally better (takes longer), but the tests are nowhere near scientific.
After shutting down, it was clear the front flexible baffles had popped back down again. It seems fixing this is important.
I’ll have to try reducing throttle just a hair in the climb like Thomas mentioned. If it works then I might be done messing with it after the above.
First takeoff seemed to go pretty well. The #4 did not get over 400 until about 1000 feet. Subsequent takeoffs started showing the old behavior of getting to 450. It seems marginally better (takes longer), but the tests are nowhere near scientific.
After shutting down, it was clear the front flexible baffles had popped back down again. It seems fixing this is important.
I’ll have to try reducing throttle just a hair in the climb like Thomas mentioned. If it works then I might be done messing with it after the above.
Instead of going with the Aviat #4 cylinder baffle modification I first tried putting a thick washer between that baffle and the cylinder. To accommodate this the screw holes that hold the corner of the baffle together needed to be slightly elongated. I've got about 100 hrs with this and it seems to help; my #4 isn't the hot cylinder on climb out; my #1 is.
I also removed the 2 deflectors riveted to the lower inlet baffle and put nutplates in instead of rivets. This allows me to make front deflectors of different heights and switch them out. I lowered the height in front of #2 and it didn't make a significant change (I left it anyway because it did no harm either). I also raised the height in front of #1 and again it didn't seem to make a big difference.
For what it's worth, experience with other aircraft has shown me that more cooling air comes in the left (pilots point of view) cooling intake than the right. This means that within the upper deck plenum the higher pressure air has to equalize by passing over the engine left to right. This indicates to me that having the oil cooler intake behind #4 (right side) is exactly wrong. I'm planning on moving this intake to the center. Of course this is when I both have the spare time and don't want to fly the airplane for a while (not!). That's why it's still an idea and not done.
Just information on what I've played with - not claiming to have any (good) answers.
I also removed the 2 deflectors riveted to the lower inlet baffle and put nutplates in instead of rivets. This allows me to make front deflectors of different heights and switch them out. I lowered the height in front of #2 and it didn't make a significant change (I left it anyway because it did no harm either). I also raised the height in front of #1 and again it didn't seem to make a big difference.
For what it's worth, experience with other aircraft has shown me that more cooling air comes in the left (pilots point of view) cooling intake than the right. This means that within the upper deck plenum the higher pressure air has to equalize by passing over the engine left to right. This indicates to me that having the oil cooler intake behind #4 (right side) is exactly wrong. I'm planning on moving this intake to the center. Of course this is when I both have the spare time and don't want to fly the airplane for a while (not!). That's why it's still an idea and not done.
Just information on what I've played with - not claiming to have any (good) answers.
Snowbirdxx
Well-Known Member
Tried that, No effect at all
Assuming you are referring to the moving of the oil cooler intake to the center of the rear baffle:
did you lessen the intake area and then expand it to the cooler? I'm thinking this is an integral part in having it work?
I'm pretty curious about all of this. On my Rocket I've made provisions to pick-up cooling air for the oil cooler at the very mouth of cowl. There is a 10 deg F delta between the inlet air and air feeding the oil cooler at the rear baffle. Plus I'm thinking having no "hole" in the upper plenum it would allow better pressure distribution through the cylinders. Your thoughts????
Snowbirdxx
Well-Known Member
Agreed in theory. Tried all that with different intakte Locations diametral etc.
LOWandSLOW
New Member
+1 to Flying Dave’s tape comment. I tried several different heights on #1 and #2 and finally solved this with a combo of front baffles, and a #3 factory bypass. All 4 run similarly 380-395 in cruise now, hotter in climb (full mixture). It took a lot of monkeying around but it got there.
belloypilot
Active Member
I'd be interested to know what power settings you're using when getting those CHTs in cruise. My typical cruise at 3500-5500 ASL is 23" MP, 2000 RPM and 7 gph which gets me 100 KTAS and CHTs in the 340-350 range. Those are summer numbers, with OAT in the high teens or low 20s C, and running 31" bush wheels.
harry harper
Active Member
My numbers are similar if not a bit cooler. I have done every mod Iv'e ever read about on this site including re jetting the carb..and the enigmatic "Tractor Baffle". Havent heard a peep about that mod of late.
LOWandSLOW
New Member
I’m on WIP 2100 amphib in the summer so I have to run harder or it really plows. Typically 25”/2100 and 7.8-8 gph, but only 90ktas with the drag of the floats at 2500-3500. I run a two blade hartzell trailblazer. I think the computer says that’s about 66% power. That’s at +23C to +30C at that altitude. CHT’s seem to drop about the same as OAT below that for me.
LOWandSLOW
New Member
It is wonderful when the tractor baffle fairy shows up in your hangar overnight and one of those appears.
Snowbirdxx
Well-Known Member
My #4 jug was the hottest in CHT on almost all powersettings being 30° and more above the others. EGT was never the hottest.
To solve the problen I increased the airflow around the cylinder. I pushed a 1/2 " X 1/2 " about 4.5 inch rectangular angle profile between the cylinder and the baffle. The ends of the angle towards the baffle. This widened up the space between baffle and the ribs. The angle stays there and CHT on #4 dropped by 35 deg, even more in the high power climb. Inexpensive and removable if not liked. I did not even take the top cowl off to hammer the angle in, just inboard where the mag-harness is routed through the baffle.
To solve the problen I increased the airflow around the cylinder. I pushed a 1/2 " X 1/2 " about 4.5 inch rectangular angle profile between the cylinder and the baffle. The ends of the angle towards the baffle. This widened up the space between baffle and the ribs. The angle stays there and CHT on #4 dropped by 35 deg, even more in the high power climb. Inexpensive and removable if not liked. I did not even take the top cowl off to hammer the angle in, just inboard where the mag-harness is routed through the baffle.