So after i replaced my engine, timing chains and guides, phasers, it dropped a valve and damaged the head and cylinder wall. I still have the block from the original engine but no main caps. question is can i use the main caps from one 5.4 in another 5.4. Im on a tight budget and cant afford another engine.

 

Possibly. The caps would have to be machined to fit and have to be align bored on the different block. I'm speaking from knowledge gained working on a 1972 Pontiac 455. Your engine may be different? On the 455, the cap was ground on the ends to make it a tighter fit and then align bored through all of the caps.

 

Please do not take this as fact. I believe you can, but they must be retained in the same physical position in the block, front to rear.