Cam chain problems
The cam chain assembly on this bike has a life expectancy of around 24,000 miles. A random metallic top end rattle indicates problems, consistent rattle is usually the valve clearances.
First try adjusting the chains tension as described in the Honda manual thus, run the engine at tick over and release the cam chain adjuster locking nut. Loosen the locking bolt, now tighten in the reverse order. If correct tension is achieved you will hear a slight whine as the revs rise and fall.
Second if the above fails to silence the rattle, remove the 'blanking' 10mm bolt found between the front engine mounting plates. Now with a small screwdriver placed down the blanking hole repeat the Honda procedure but this time apply light pressure onto the adjuster with the screwdriver and then tighten the locking bolt. If correct tension is still not achieved, it is highly likely that either the cam chain is worn or, the adjuster has seized. Find out which as follows.
Remove the cylinder head cover. Unscrew the two 10mm bolts that hold the rear facing tensioner blade by 5mm. Release the cam chain adjuster locking nut and bolt and see if the blade jumps upward, if so, tighten the adjuster and locknut then tighten the two 10mm retainer bolts. Take care that the chain is not too tight, if so repeat the process but this time only undo the bolts by say 3mm etc. This method removes the problem of the chains backlash, present when running.
Finally if all this has failed to silence the noise, a minimum of a top end strip will be required if using a soft rivet chain replacement or a full tear down of the whole engine to replace with an endless chain (recommended by Honda).
When replacing the chain always replace the tensioner blade, tensioner guide and both tensioner dampers. The tensioner blade will have sustained the most wear & tear and I also replace the dampers as these shrink with time and can then fall out when removing or replacing the cam chain tensioner blade, usually dropping into the crankcases ... arrgh! Some also replace the springs, do check while apart that the assembly moves like a Jack in the box when the lock screw is loosened.
Service limits
Cam chain guide blade is minimum 5mm in the centre. When new 6mm raised centre and 4.5mm at each edge.
Cam chain tensioner slipper is minimum 3mm in the centre. When new 4.5mm, two grooves will be worn into this by the cam chain
Honda Part numbers
14401-333-003 Chain, cam
14501-323-000 Damper, cam chain tensioner
14545-333-000 Slipper, cam chain tensioner
14620-333-000 Guide, cam chain
90016-286-000 Bolt, tensioner setting
12391-333-000 Gasket, cylinder head cover
Tsubaki make 219T82L split cam chains with a soft rivet & DiD make endless 219T82L chains if you want to save money over Genuine Honda prices.