HI, why are there 2 kinds of pushrods(4 steel & 4 aluminium) in my engine and can i change them to all steel as i have bought a tappet set and pushrods that only have 22,600 miles on them(my engine is at 77,700 miles)and my tappet arms are very worn(8 owners before me),iwas gonna change them at the weekend when i noticed the aluminium pusrods in the engine so i left it,also i was gonna change the injectors,injector rail and fuel pressure regulator all from the same 22,000 engine as i changed the throttle body last weekend and it has made a huge difference. any help please.

You can do, but I think you need to set the clearances to be all the same as they would be for the steel ones - the aluminium was supposed to help with them being quieter when cold or something. Certainly I've run all steel ones in some of my cars without issue and the older Fav engines used to be all steel anyway....