Cam chain problems
The cam chain assembly on this bike has a life expectancy of around 20-40,000 miles. A random metallic top end rattle indicates problems, consistent rattle is usually the valve clearances.
How it works
Think of an archers bow, pressure supplied by the dual sprung adjuster presses through the hinged arm to the slipper thus bending the rear slipper in toward the cam chain.
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, 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.
Cam chain guide blade is minimum 5mm in the centre. When new 6mm raised centre and 4.5mm at each edge. After 10,000 mile this guide blade will show little or no wear at all.
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. It is this blade that sustains the most wear.
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
12391-333-000 Gasket, cylinder head cover
90016-286-000 Bolt, tensioner setting.
Dimensions of the above bolt:-
Overall length 28mm, M8 8mm, M6 15mm + 1mm at the end, 4mm between the two threads. Manufacture using 10mm hex stainless steel bar.
DiD make endless 219T82L chains if you want to save money over Genuine Honda prices. DiD also list a heavy duty 219FTS(S) DHA and 219FTH that has 5% & 11% extra tensile and 25% & 27% extra fatigue strength respectively, recommended by some of the ‘CB400F Yahoo! group’ members. The extra strength comes from its side plate design, using an oval plate rather than standard figure of eight shape. Try Orwell Motorcycles Ltd for all DID options. Also listed is a soft rivet for anyone not wanting to do a bottom end strip.
In this case use the following with great care
1 A suspected seized adjuster may be released with a suitable size of flat bottomed punch and tap with a hammer down the blanking bolt hole. The chain adjuster is now likely too tight and cam chain will whine. You will have to remove the rocker cover and the camchain slipper. Try to free the adjuster by pushing alternately on the adjuster and then the slipper end of the arm, a little light oil down the blanking bolt hole will help. If this fails try the next option after pushing the slipper end of the arm first i.e. so you have a slack chain.
2 The blanking bolt may be replaced with a hex bolt long enough to reach the adjuster. It will need a few threads ground off first, then it can be screwed in till the chain rattle is silenced and locked off with a nut. WARNING: If over tightened the chain could snap!! and or the slipper tensioner blade will wear very quickly. I personally do not recommend this and would always strip the engine.
3 A loose cam chain can damage the bottom arm and wear into the crankcases.
Finally: Are you sure it is cam chain rattle. Badly adjusted carburettors make these engines rattle/knock.