Flying.eth
MEMBER
Started flying my newly refinished experimental cub. I decided to have cylinders
rehoned and new rings due to a little bit of rust on the walls. Engine came out of a certified cub with 56 hours since lycon overhaul with port and polish. Removing cylinders to check cam and followers found heavily domed pistons. Called lycon with part number and determined 10:1s with deck height shaved for another half point boost. Running one pmag set 2 ATDC and jumper in. Rear mounted seven row airflow designs cooler which is supposed to run 5-15 degrees cooler than standard seven row.
Its been cold here in Alaska and during break in with cruise prop nice low CHTs 330ish running hard and high airspeed. They actually come up when backing off to more normal cruise power settings, must be where pmag starts advancing. Averaged 12.5 gals
/hr during initial break in flights. Climbs can send hot cylinder over 400 if not careful. Switching pmag off definitely drops cht. Cruising 75% power on subsequent flights hottest cylinder can be up to 370 Which comes up at lower power settings where other one drops. Inverse at higher settings hot cylinder drops(#4) and #3 comes up. Generally around 20-30 degree difference. Oil temps only getting 120ish. Pressure barely drops if at all. Suspected gauge but felt sump and cooler at shutdown and it’s barely warm to the touch. Infrared thermometer showing it a bit over 100. Started taping off cooler and now have fully blocked. Getting 130 ish now and cooler and sump feel warm at least on shutdown. Sump measuring 130ish with thermometer. Interestingly didn’t change CHT on #4. Current thought is the Selkirk cowling. It is open around air filter and carb to lower engine with a big exit right there that has a lip for lowering pressure. Also big cheeks at 3.5 inch gap. Thinking there must be tons of cold air blasting the sump and carb. Lots of surface area cooling the oil.
Next step is to verify sender accuracy with boiling water at first oil change. I’ll also probably retard pmag a little more and/or try disconnecting manifold pressure tube. If CHTs continue to be high might have to look at carb work to get more flow.
Anyone experience anything like this? Anyone have experience with Selkirk cowl?
rehoned and new rings due to a little bit of rust on the walls. Engine came out of a certified cub with 56 hours since lycon overhaul with port and polish. Removing cylinders to check cam and followers found heavily domed pistons. Called lycon with part number and determined 10:1s with deck height shaved for another half point boost. Running one pmag set 2 ATDC and jumper in. Rear mounted seven row airflow designs cooler which is supposed to run 5-15 degrees cooler than standard seven row.
Its been cold here in Alaska and during break in with cruise prop nice low CHTs 330ish running hard and high airspeed. They actually come up when backing off to more normal cruise power settings, must be where pmag starts advancing. Averaged 12.5 gals
/hr during initial break in flights. Climbs can send hot cylinder over 400 if not careful. Switching pmag off definitely drops cht. Cruising 75% power on subsequent flights hottest cylinder can be up to 370 Which comes up at lower power settings where other one drops. Inverse at higher settings hot cylinder drops(#4) and #3 comes up. Generally around 20-30 degree difference. Oil temps only getting 120ish. Pressure barely drops if at all. Suspected gauge but felt sump and cooler at shutdown and it’s barely warm to the touch. Infrared thermometer showing it a bit over 100. Started taping off cooler and now have fully blocked. Getting 130 ish now and cooler and sump feel warm at least on shutdown. Sump measuring 130ish with thermometer. Interestingly didn’t change CHT on #4. Current thought is the Selkirk cowling. It is open around air filter and carb to lower engine with a big exit right there that has a lip for lowering pressure. Also big cheeks at 3.5 inch gap. Thinking there must be tons of cold air blasting the sump and carb. Lots of surface area cooling the oil.
Next step is to verify sender accuracy with boiling water at first oil change. I’ll also probably retard pmag a little more and/or try disconnecting manifold pressure tube. If CHTs continue to be high might have to look at carb work to get more flow.
Anyone experience anything like this? Anyone have experience with Selkirk cowl?
