Shim(s) are used to preset chain tension , then hydraulic takes up remaining slack when running. Running it with a chain out of tension spec could cause it to jump a tooth when the engine is shut down on a compression rebound cycle. There's an actual tool that tells how many shims are needed, plus checks need to be done with each cyl for the checks at TDCC but for now, take note of the slack in the front chain when it's TDCC. Top dead center compression. Rule out any other reasons for this discrepancy like worn rear guides or whatever for the rear so much looser. Turn engine counter clockwise only until rear is on TDCC. Note the slack and add shims until it matches the front for play you previously noted. Neither should be tight completely but a small slack present. Generally when slack is too much they make a rattling sound when engine is first started.
