Belt drive conversion kit. Replaces the chain drive with quiet, low maintenance cog belt system. Before purchase please view the conversion video here. Requires grinding an additional flat into the crankshaft. OR - you can send your compressor in and we will do the upgrade work for you - there is a $50 shop fee, you pay for the parts and shipping both ways - (contact us via email in this case: firstname.lastname@example.org ). If you decide to have us upgrade both the drive AND the pistons, there is only one $50 for both.