[A26B]

Normal occurance after timing cams AND after removing the manual chain tensioners.

As you rotate the cams via crankshaft, there comes a point where camshafts don't have very much tension from compressed valve springs. Likewise, there are certain points in the rotation that have a significant amount of valve spring pressure working against the camshaft (and corresponding tension on the secondary timing chain).

As the camshaft continues to rotate the open valve(s) pass over the lobe nose(s) and spring pressure accelerates cam rotation to that place in the rotation where there is much less spring pressure against the camshaft, and the chain slack is jerked tight. Thats the "slap" you hear. It's because the hydraulic tensioners are not pressurized from engine oil, only a bit of tensioner spring pressure.

With 4 cams experiencing the same thing at different points in engine/cam rotation, there will be several chain slaps as you rotate manually.

This is the same thing that you hear on startup, for that brief moment until engine oil pressure builds and the chain tensioner exerts pressure against the slack chain.

It's a tad difficult to explain in words. If you recall placing the camshaft down into the journals in the head, there is that spot where it nearly lays flat, hence not much valve spring compression. As the cam rotates into that position, from high spring pressure, is when the "slap" happens.