If you are looking for a replacement part for a John Deere tractor, you should consider purchasing a Powerblock. These are easy to install and are extremely inexpensive. These blocks have a bore of six inches and are designed to increase power. The main differences between these and the original JD power blocks are the bore size and compression ratio. A G Powerblock has a larger bore and is more powerful than the original. It will need to be installed by a machine shop if you want to use it for farming purposes.