OS 46 FX - weak - worn? How to tell
06-24-2003, 09:02 PM
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OS 46 FX - weak - worn? How to tell
Recent symptoms - bearings feel a little rough, but I never got any grey or brown exhaust oil - always clear. I haven't pulled the bearings yet, but from the case, they look ok. Suddenly started sagging in flight at higher powers (started and idled fine), until wouldn't run at power any more. Feels like the connecting rod is loose either at the crankshaft or the wrist pin. There's minor scoring of the liner as well.
Which would be the prime cause for loss of power - con-rod wear or cylinder wear (bearings are still free)? How would I measure the rod/pin wear without a micrometer?
Thanks in advance!!
Keefer
Which would be the prime cause for loss of power - con-rod wear or cylinder wear (bearings are still free)? How would I measure the rod/pin wear without a micrometer?
Thanks in advance!!
Keefer
06-25-2003, 02:30 PM
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OS 46 FX - weak - worn? How to tell
On most model engines, the main sign that they're wearing out is that the idle and acceleration starts to go. That's the earliest sign that the compression seal is worn. Top RPM will eventually start to go, too. Some modelers get a bit more life to an engine by adding oil to their fuel. This helps the seal, but is only a very temporary solution.
Bearing roughness is usually caused by corrosion. You may not have much visible, but you'll likely find small pits in the bearing race and the balls. This would account for the roughness.
Corrosion on bearings usually winds up being strewn through the rest of the engine. Rust is iron oxide, which is a dandy abrasive, and will contribute greatly to a worn piston/cylinder fit.
The connecting rod to crankpin fit is usually something to worry about on really, really, old or well-used engines. If the fit gets larger than .006"-.008", then you're starting to have enough slop to worry about. Usually, though, you can only see oil squeeze and not actual movement of the crankpin in the rod end. Many people see oil squeeze and think it's movement. You have to look carefully, it can be a bit deceptive. Any visible movement means you have to actually check the clearance.
Bearing roughness is usually caused by corrosion. You may not have much visible, but you'll likely find small pits in the bearing race and the balls. This would account for the roughness.
Corrosion on bearings usually winds up being strewn through the rest of the engine. Rust is iron oxide, which is a dandy abrasive, and will contribute greatly to a worn piston/cylinder fit.
The connecting rod to crankpin fit is usually something to worry about on really, really, old or well-used engines. If the fit gets larger than .006"-.008", then you're starting to have enough slop to worry about. Usually, though, you can only see oil squeeze and not actual movement of the crankpin in the rod end. Many people see oil squeeze and think it's movement. You have to look carefully, it can be a bit deceptive. Any visible movement means you have to actually check the clearance.
