Geek1945
Well-Known Member
Hello 2 Stroke Aviation Guru's,
I'm concerned about 2 stroke engines suddenly stoppages in-flight. After examining several failed cranks it would appear these factors are major players; lack of lubrication at operating speed, bearing failures (oil quality, caged vs. loose full fill bearings, WOT operation above rated limit, design specifications compromised to accommodate ease of assembly of bearings)
It is my understanding it is better to slightly unload the engine so full RPM is achieved unlike a 4 stroke engine?
Usually bearing failure is a result of lubrication failure, yet in the Personal Watercraft (PWC) situation with oil metering pumps these crankshaft bearing failures continues to occur. It would appear once an oil filter clogs it is either bypassed or no action is taken. Now either the oil pump is failing to deliver adequate lubrication or the bearings are not properly spec's. For initial lubrication testing my intent is to use 32:1 fuel/synthetic oil mix and reconfigure the oil pump range to supply oil from 3K minimum to 6.5K at full throttle. This should provide >24:1 (more oil mix at full throttle).
I have searched for high quality ABEC bearings from brand name OEM's for replacement.
Roller and Cage Assemblies
http://www.ntnamericas.com/en/websi...oller_bearings_handbook_cat_9013-e_lowres.pdf
Unfortunately neither caged nor loose needle bearings are available in hi-precision grades although ceramic are available.
Ceramic Ball Bearings
Microblue Racing | The competition will be tough. We've got what you need to win!
An examination of failed cranks reveals out-of-round needles from rod pounding and loss of polished surfaces. This is what appears to be happening with most PWC crankshaft bearing failures. Several bearings dowel pins were missing and shim stock was used to secure bearings.
I'm older than water so I was taught to shellac all paper fiber gaskets to prevent migration of air into intakes are new gaskets impervious to leakage? Something must be done to mitigate these failures rather than '2 strokes always live short lives'.
In an effort to reduce/eliminate piston related problems, use MSO2 skirt wear/underside for oil shedding and ceramic crown coatings for heat insulation. My research has failed to find similar bearing coatings, so added oiling at higher speeds seems a viable option. Would enlarging crankcase oil bleeder holes be a viable option? Naturally this additional oil may require more frequent de-carbonizing yet anyone using synthetic should experience less carbon build-up?
BTW carbon can be easily disposed of using paint remover w/methylcloride (wear gloves it burns skin and will discolor aluminum), the process should be stopped when a wooden stick shows loosen carbon. Exhaust plumbing can be rinsed with water once removed from engine.
Reading engineering technical literature on needle bearings my options are caged which OEM uses or loose full fill. Now cage = speed @ higher bearing loading whereas loose = lower speed @ lower bearing loading. Now I'm wondering which bearing configuration provides the best performance with longest MTBO? Actually crank dis-assembly is acceptable ONCE doing the repair again is insanity especially pressing the crankshaft apart/reassembly. Cylinder wear out should occur BEFORE crank failure. The engine is a Suzuki 2 stroke 639cc liquid cooled twin 64HP @ 6500RPM de-rated <50HP to in aircraft application.
Reviewing porting procedures seems to have a beneficial effect, especially chamfering cylinder ports to prevent rings from catching squared edges. Has anyone done a porting job, and what were your experiences?
It would seem installations of O2 sensors would be the best way to determine A/F ratio what are your thoughts on this?
I have also observed inconsistent cylinder cooling which may be caused by a thermostat failing to meter/modulate coolant flow in PWC cold water. Would additional distributed inlets lead to more equal cylinder temperatures? How about reverse flow cooling hot heads first? Has anyone wrapped insulating material on the exhaust system?
Has anyone used Iridium spark plugs to reduce fouling? How about using copper braid on spark plug leads to reduce RFI?
Finally I was wondering if a catalytic converter would make a good muffler while cleaning 2 strokes dirty exhaust.
Thanks for reading this, and I'll be waiting for your recommendations. Ed
I'm concerned about 2 stroke engines suddenly stoppages in-flight. After examining several failed cranks it would appear these factors are major players; lack of lubrication at operating speed, bearing failures (oil quality, caged vs. loose full fill bearings, WOT operation above rated limit, design specifications compromised to accommodate ease of assembly of bearings)
It is my understanding it is better to slightly unload the engine so full RPM is achieved unlike a 4 stroke engine?
Usually bearing failure is a result of lubrication failure, yet in the Personal Watercraft (PWC) situation with oil metering pumps these crankshaft bearing failures continues to occur. It would appear once an oil filter clogs it is either bypassed or no action is taken. Now either the oil pump is failing to deliver adequate lubrication or the bearings are not properly spec's. For initial lubrication testing my intent is to use 32:1 fuel/synthetic oil mix and reconfigure the oil pump range to supply oil from 3K minimum to 6.5K at full throttle. This should provide >24:1 (more oil mix at full throttle).
I have searched for high quality ABEC bearings from brand name OEM's for replacement.
Roller and Cage Assemblies
http://www.ntnamericas.com/en/websi...oller_bearings_handbook_cat_9013-e_lowres.pdf
Unfortunately neither caged nor loose needle bearings are available in hi-precision grades although ceramic are available.
Ceramic Ball Bearings
Microblue Racing | The competition will be tough. We've got what you need to win!
An examination of failed cranks reveals out-of-round needles from rod pounding and loss of polished surfaces. This is what appears to be happening with most PWC crankshaft bearing failures. Several bearings dowel pins were missing and shim stock was used to secure bearings.
I'm older than water so I was taught to shellac all paper fiber gaskets to prevent migration of air into intakes are new gaskets impervious to leakage? Something must be done to mitigate these failures rather than '2 strokes always live short lives'.
In an effort to reduce/eliminate piston related problems, use MSO2 skirt wear/underside for oil shedding and ceramic crown coatings for heat insulation. My research has failed to find similar bearing coatings, so added oiling at higher speeds seems a viable option. Would enlarging crankcase oil bleeder holes be a viable option? Naturally this additional oil may require more frequent de-carbonizing yet anyone using synthetic should experience less carbon build-up?
BTW carbon can be easily disposed of using paint remover w/methylcloride (wear gloves it burns skin and will discolor aluminum), the process should be stopped when a wooden stick shows loosen carbon. Exhaust plumbing can be rinsed with water once removed from engine.
Reading engineering technical literature on needle bearings my options are caged which OEM uses or loose full fill. Now cage = speed @ higher bearing loading whereas loose = lower speed @ lower bearing loading. Now I'm wondering which bearing configuration provides the best performance with longest MTBO? Actually crank dis-assembly is acceptable ONCE doing the repair again is insanity especially pressing the crankshaft apart/reassembly. Cylinder wear out should occur BEFORE crank failure. The engine is a Suzuki 2 stroke 639cc liquid cooled twin 64HP @ 6500RPM de-rated <50HP to in aircraft application.
Reviewing porting procedures seems to have a beneficial effect, especially chamfering cylinder ports to prevent rings from catching squared edges. Has anyone done a porting job, and what were your experiences?
It would seem installations of O2 sensors would be the best way to determine A/F ratio what are your thoughts on this?
I have also observed inconsistent cylinder cooling which may be caused by a thermostat failing to meter/modulate coolant flow in PWC cold water. Would additional distributed inlets lead to more equal cylinder temperatures? How about reverse flow cooling hot heads first? Has anyone wrapped insulating material on the exhaust system?
Has anyone used Iridium spark plugs to reduce fouling? How about using copper braid on spark plug leads to reduce RFI?
Finally I was wondering if a catalytic converter would make a good muffler while cleaning 2 strokes dirty exhaust.
Thanks for reading this, and I'll be waiting for your recommendations. Ed
