Sometimes when lifting the rocker box, one of the pushrods sticks in the rocker arm, before dropping back down the pushrod tunnel and ending up on the rim of the follower, not down in the centre where it should be.
Best to start again from the beginning.....Pushrods out, check each for straightness and bow by rolling on a flat surface, then replace in their original positions with a dab of grease to hold them in place. Exhaust ones are longer, these are the two centre ones.
With the plugs removed you could try kicking over before you take the rocker box off, this time without the tappet covers on. Listen for the noise, it may have already been there but not noticed. Look for a rocker adjuster witness mark on one of the covers, this is a clue to a mis placed pushrod. Don't forget you have to readjust the tappets anyway, as the thickness of the gaskets positions the rocker arms in relation to the valves and camshaft.
Allow plenty of time for this job, well worth reading how other folks do it. The pushrod comb, torches, rubber bands, dental mirrors, wire hooks, witchcraft, faith, miracles all have played their part.....
Swarfy.
Additional. Gynaecological skills also useful....
