cpd
Well-Known Member
- Joined
- Jul 24, 2008
- Messages
- 147
I have exhausted my brain and the brains of several other engine experts with an issue im having with my Rotax 277UL (free air) so I thought I would ask you
I acquired this engine a decade ago, its hours and condition largely unknown. I cleaned it up, rebuilt its carb and mounted it up last spring with a 2.58:1 gear drive swinging a 3 blade ultraprop. static runs with stock carb jetting were fine so I attempted a short flight, 5 minutes in while running at 6000rpm with a cht of 430 and an EGT of 1050 the piston burned through on the intake side and the engine seized. (neither me or the plane were harmed thankfully).
I rebuilt the engine last October, replaced crank seals and installed a piston and cylinder from my fan cooled 277 ( a known good motor with about 80hrs run time). Now the real fun has began.
on the first break in run I had to abort early as at anything over 5k rpm the CHT quickly went pas 475deg. I built a simple cooling shroud around the head and increased the main jet size from the stock 148 to a 150 then a 152. No matter what combination of jets, needle clip positions or shroud designs I try, In an attempt to keep the CHT below 450 im jetted so rich on the main at 152 that the EGT never exceeds 900 deg at any power setting and im starting to foul plugs.
here are the particulars for my engine:
tractor configuration, free air cooled
all temps recorded in flight at 65deg OAT and 40mph airspeed
premix at 40:1
Bing 54 carb and stock exhaust.
max static rpm: 6340, in flight 6450
EGT at WOT: 850deg
CHT at WOT:400deg
EGT at 6000rpm: 900
CHT at 6000rpm: 450
EGT at 5500rpm: 950deg
CHT at 5500rpm: 440deg
EGT at 5000rpm: 900deg
CHT at 5000rpm: 425deg
EGT at 4500rpm: 800deg
CHT at 4500rpm: 375deg
I have checked and verified timing multiple times
I have pressure checked the crankcase, no leaks
I have checked piston and cylinder clearance
I have checked, checked, and rechecked gauges for accuracy
most people cant get their free air 277s to reach 375deg on a hot day and I cant keep mine at 450 or under unless I jet it so rich it doesn't want to run well, at full power the carb is aspirating fuel out the intake but she still wont stay cool. if I go to a 146 main jet to get the EGTs up to 1100deg then the CHT will skyrocket past 500deg at anything over 5000rpm.
what gives, this plane is going to miss another flying season if I cant sort this out. so please lay any and all advice on me, im going to get a priest and some holy water.
Chris
I acquired this engine a decade ago, its hours and condition largely unknown. I cleaned it up, rebuilt its carb and mounted it up last spring with a 2.58:1 gear drive swinging a 3 blade ultraprop. static runs with stock carb jetting were fine so I attempted a short flight, 5 minutes in while running at 6000rpm with a cht of 430 and an EGT of 1050 the piston burned through on the intake side and the engine seized. (neither me or the plane were harmed thankfully).
I rebuilt the engine last October, replaced crank seals and installed a piston and cylinder from my fan cooled 277 ( a known good motor with about 80hrs run time). Now the real fun has began.
on the first break in run I had to abort early as at anything over 5k rpm the CHT quickly went pas 475deg. I built a simple cooling shroud around the head and increased the main jet size from the stock 148 to a 150 then a 152. No matter what combination of jets, needle clip positions or shroud designs I try, In an attempt to keep the CHT below 450 im jetted so rich on the main at 152 that the EGT never exceeds 900 deg at any power setting and im starting to foul plugs.
here are the particulars for my engine:
tractor configuration, free air cooled
all temps recorded in flight at 65deg OAT and 40mph airspeed
premix at 40:1
Bing 54 carb and stock exhaust.
max static rpm: 6340, in flight 6450
EGT at WOT: 850deg
CHT at WOT:400deg
EGT at 6000rpm: 900
CHT at 6000rpm: 450
EGT at 5500rpm: 950deg
CHT at 5500rpm: 440deg
EGT at 5000rpm: 900deg
CHT at 5000rpm: 425deg
EGT at 4500rpm: 800deg
CHT at 4500rpm: 375deg
I have checked and verified timing multiple times
I have pressure checked the crankcase, no leaks
I have checked piston and cylinder clearance
I have checked, checked, and rechecked gauges for accuracy
most people cant get their free air 277s to reach 375deg on a hot day and I cant keep mine at 450 or under unless I jet it so rich it doesn't want to run well, at full power the carb is aspirating fuel out the intake but she still wont stay cool. if I go to a 146 main jet to get the EGTs up to 1100deg then the CHT will skyrocket past 500deg at anything over 5000rpm.
what gives, this plane is going to miss another flying season if I cant sort this out. so please lay any and all advice on me, im going to get a priest and some holy water.
Chris
