Slam Valve Motor, supplying efficient steam engines for homeowners and professional solar installers
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Engine lifespan

Generally gasoline engines and pumps do not come with a warranty that reflects their actual lifespan. The reason is, the lifespan depends a lot on how you use it. For example, the lifespan of anything with a piston at over 1000 RPM is proportionate to 1/RPM^3. If you bought a car with an engine half the size of another, and it ran at twice the RPM to give the same horsepower, it would have 1/8 the lifespan of the other car. Small differences in RPM can relate to big differences in lifespan.

The engine lifespan predictor is based on lifespan comparisons of a number of different styles of engines. It assumes nominal quality given the technology listed, proper lubrication, no rust, and no particles entering the motor. Engine quality is generally at least a factor of 2 in service life from a lower quality motor to a higher quality motor of the same type, the spreadsheet does not account for this. Also all piston manufacturers will produce some units which have defects and will not live up to their expected service life.

Engines wear out in two ways. The rings slide on the cylinders enough times to wear a bigger gap than the rings can compensate for. This leads to poor seal and rapid degradation. This gives a lifespan which goes with 1/RPM.  The other way appears similar but has different causes. The main bearing wears, becomes loose, fails to hold the piston in the middle of the cylinder,  and causes the rings to wear faster causing a gap that cannot be sealed.  Main bearing wear relates to the forces on the main bearing and is a sum of acceleration force on the piston and torque. These factors have a strong dependence on RPM. Download the engine lifespan predictor under spreadsheet tools to see how different engine styles age at different loads and RPMs. See the 7000 RPM aluminum sleeve weed whacker face off against the 1200 RPM hardened steel Diesel generator.