A rattling or grinding noise coming from the mid-center and/or top of the engine most often indicates loose cam chains. The noise is more audible at lower engine RPM, or during deceleration.

The noise is caused when the cam lobes flip over on the rocker arms. The rattling or grinding sound happens because the chain goes loose between the sprockets or on the tension side of the chain.

Honda has revised the design of the cam chain tensioners to provide more tension arm travel, more tension, and an improved locking mechanism. The revisions were due to finding that the tensioner was running out of travel and not tightening a cam chain that was still within length spec. The best way to determine if you have loose cam chains is to physically inspect them.

With the valve covers and alternator cover removed and beginning at TDC 1-3, rotate the engine with the alternator bolt for two complete revolutions. Stop at each 90° interval, and check the tightness of the chain just below the uppermost surface of the chain guide. The chain should be snug against the guide at all of the intervals. If at any interval the chain is loose, you can benefit from installing the updated cam chain tensioner assemblies. Installing the revised tensioners works to tighten the cam chain in most circumstances. There are a few instances where the chain is stretched past the wear limit, or is looser in one spot than others due to uneven stretch. The corrective action would be to replace the cam chains and install the revised tensioner assemblies.