Engine information on popular MTD Models
MTD 2554 PRO
Original Model: Kohler CV25-69534
The original engine had a 1-1/8"x3-5/32" Shaft on it. If you buy one with a longer shaft you can either cut it off or add a bushing at the bottom to hold the pulley in place. The shortblock for the 69534 spec is the 24522264 You may have to use minor parts from your original engine to make this work for you.
MTD 990 Garden Tractor
Original Model: Briggs Single Cylinder horizontal 16 hp cast iron
This cast iron Briggs has a starter generator on it and drives of both sides of the engine.
MTD MMZ 1848
Original Model: Briggs 350777 Vanguard
When replacing the Vanguard with one of the Vanguard engines listed you may have to use minor parts from your original engine to make this work for you. NOTE: Some of these units came with a Briggs Opposed twin engine 42A707-1238. This engine is totally different than the Vanguard engine. They are not interchangeable.