Bill is correct.

The ST 2000, 2500, and 3000 all use the same exact crank and stroke combination. That means the threads on the engines are all the same.

Only difference in the engines is the size of the main journal. The journal is the same size in the 2000 and 2500, but its slightly bigger in the 3000 to handle the larger connecting rod.

The 2000 and 2500 use the same connecting rod. The 2500 just has a bigger cylinder bore.

At first glance, all the engines appear to be the same on the outside. But if you look closely, the 3000 has a slightly taller cylinder. ST made the crankcase and connecting rod taller to reduce the amount of rotating mass on the larger engine. Still, the same stroke as the smaller 2000 and 2500 engines.

As you might have noticed, the 3000 will wind up faster when you punch the throttle. Thats because it has such a large bore, relative to the stroke. Engines with large bore and small stroke will always wind up faster than an engine with a long stroke and small bore.

The short stroke motors will usually have more top end HP and turn more RPM's, and the long stroke engine will have more low end torque, and swing a bigger prop at lower RPM's.

By the way: Does anyone know the Max RPM of the ST3000 engine? I have one and I don't want to wind it up too much.