tractor engine

[dai stinch]

Help i have a mf 135 tractor with a perkins ad3 152 diesel engine i started her the other day to find i had a nasty knocking sound from within the engine, my first thought was bottom end the sound comes from up higher thought it might be a blocked injector i thought ( Does any one know how to take them out safely ) not sure tho its only a 3 cylinder and sound like it not firing on all 3 ? she hasent done a lot of hours from new and only then light work mowing harrowing etc we had her from new 35 years ago, checked the sump for diesel all clear there just incase the lift pump diaphram split nice clean oil (oil changed a month ago ) would appreciate any advice or help