You replace the crankshaft every overhaul? Why is that — does the wear make the engine prone to failures in some way? What about the bearings? I’d be more interested in a bearing going bad and eating its way through the crankshaft.
Jim — I am no expert, that’s for sure. But the 2-stroke engine puts out a very large amount of horsepower for it’s size/weight, and the stresses on all components are enormous. Bearings are checked at 150 hours and, if within tolerance, give a good indicator of how long the crank will last. Although any of the component parts of the crankshaft assembly can fail, rod bearing failure is very destructive, and can occur with little warning. ..sometimes only seconds. Another crankshaft anomaly which is cause for rejection of the part, though rare, is worn center main bearings. Extremely rare, is actual breakage of center axis components.
Counter-intuitively, the more you run a 2-stroke engine, the longer it will last. The worst thing you can do to a 2-stroke is let it sit. Many engines go way past 300 hours without a problem, but typically their owners will use them frequently.
Keep in mind that MANY factors affect the longevity of a 2-stroke aircraft engine, not the least of which are the choice of propeller (if moment of inertia is too great, it can chew up the engine pretty quickly), proper engine mounting with vibration isolation, and proper oil mixtures. Improper oil mixture may be the most common of all mistakes made by pilots.
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You replace the crankshaft every overhaul? Why is that — does the wear make the engine prone to failures in some way? What about the bearings? I’d be more interested in a bearing going bad and eating its way through the crankshaft.
Jim — I am no expert, that’s for sure. But the 2-stroke engine puts out a very large amount of horsepower for it’s size/weight, and the stresses on all components are enormous. Bearings are checked at 150 hours and, if within tolerance, give a good indicator of how long the crank will last. Although any of the component parts of the crankshaft assembly can fail, rod bearing failure is very destructive, and can occur with little warning. ..sometimes only seconds. Another crankshaft anomaly which is cause for rejection of the part, though rare, is worn center main bearings. Extremely rare, is actual breakage of center axis components.
Counter-intuitively, the more you run a 2-stroke engine, the longer it will last. The worst thing you can do to a 2-stroke is let it sit. Many engines go way past 300 hours without a problem, but typically their owners will use them frequently.
Keep in mind that MANY factors affect the longevity of a 2-stroke aircraft engine, not the least of which are the choice of propeller (if moment of inertia is too great, it can chew up the engine pretty quickly), proper engine mounting with vibration isolation, and proper oil mixtures. Improper oil mixture may be the most common of all mistakes made by pilots.