The 12.5hp is no longer available, but an 18hp is the same physical size. If the new engine you buy does not have a 9 amp or larger alternator, you will have to change it over from your original engine. You may have to use the flywheel from your original engine since it is thicker than the newer 18hp flywheels. If you do have to change it, the shrould will also need to be changed.
