Old 12-10-2017, 04:04 AM
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Originally Posted by alloyboy View Post
It comes from industry. If and when the life of a motor is estimated then the two stroke will typically have a lesser estimated life than will a four stroke.

Take a look at BRP Rotax, the sister company of BRP Evinrude. They (Rotax) make airplane motors. Two strokes and four strokes. In aviation, an estimated life for the motor is usually provided. Rotax suggests the life of their two stroke motors to be much less, in hours, than they suggest for their four stroke motors.

This is not to say that two strokes will not exceed the life of some four strokes. Some two strokes will outlive the life of some four strokes. All things being equal however, the average life, in operational hours, of a four stroke will exceed the average life, in operational hours, of a two stroke. The pressurized oiling system of a four stroke is probably the major part of the increased life.
There is quite a difference in those engines, the 2 stroke has a very high output for its weight, about 85 % of the hp at 50% of the weight. Build it to the same hp per lb as the 4stroke for a valid comparison.