Knocking or tapping is not shims.

[mcsdex2]

7

 

[mcsdex2]

6

 

[projectSHO89]

Yep, your tensioners are worn out. Might as well order the new ones.

Steve

 

[mcsdex2]

5

 

[Yamaha V6]

Order new chains as well - if the tensioners are gone, the chains will have been "yanked" stretched out a bit. The slapping is the chain on the chain guide as the cam lobe goes beyond in-line with the valve, and the valve spring pushes the intake cam lobe past, and the slack becomes taught, pulling the exhaust cam along for the ride. Picture a string you hold in your hand with a few inches of slack; then pull your hands apart, making the string tight - this is the movement that causes the chain to move upward quickly & strike the chain guide. Over time with the string, you'll weaken it & it'll break; with the chains, they'll stretch out, and new tensioners may not eliminate the 'clack'.

Good luck & have fun getting them in there. Be sure you align the cam sprockets correctly for proper exhaust cam timing.