The Winton two-stroke diesel engines used in the "Zephyr" power units and early EMC designs, while a breakthrough in locomotive power, were an immature technology. Some of their early reliability problems were mitigated with changes to individual parts such as pistons; other solutions had to wait for a differently designed engine. For example, the first generation of pistons in the Winton engine only had about 50,000 miles of useful life, later extended to about 100,000 miles. GM's next generation diesel engine had pistons with a useful life of over 500,000 miles. The problems were most acute under the operating conditions of locomotive, rather than stationary or marine, use. Even with the problems of the Winton 201A, their maintenance regime was significantly lower than for steam locomotives.