Motorcycle Repair: 1984 cb750 nighthawk, hydraulic tappet, piston slap

Question
QUESTION: i have a 84 nighthawk and the bike runs well except for the fact that it seems to have valve noise when it is warmed up the noise is minimal(regular honda tapping) but untill it gets up to temp i get a tapping on my intake side #1 cylinder it seems to come and go sometimes louder than others i had rebuilt the bike and it worked fine but now seems to be acting up i have the belief that it is in the tappet itself as the bike still runs smooth and nothing is loose in the head is this bike known for the tappets going bad. as there seems to be nothing wrong with the valve itself

ANSWER: Jim,

tappet problems are not common, but you may
have wear on the camshaft, tappet, shim
or camshaft holders. Also the cam chain tensioner
and chain are suspects. It doesn't take much
excess clearance to make a valve assy start
to make tapping noises. Have you checked
the oil supply to the top end? A lack of oil
or oil pressure could be a problem.
Try a sounding rod or stethescope to see if
the noise can be isolated to a specific part.
Maybe the noise is travelling from some
other part of the engine, like piston slap
for example.
Have you tried different oil viscosities
to see if the noise changes?
Some noises are bad and others don't cause much
harm except to ones ears. Check out what you
can and see if it gets any louder, to warrant
a tear down.





---------- FOLLOW-UP ----------

QUESTION: by using the stethoscope with the engine still together i am able to isolate the noise to the outer valve on the left side of the intake all others seem to be running fine and very quiet do you think that with that being said that it sounds like it might be a lack of lubrication issue which should make it either the hydraulic tappet being clogged or the oil delivery line or oil chamber on the cam cover is there anything else you could think of.

Answer
Jim,

with the noise as you described,
I suspect a bad tappet or possibly
cam wear, I can't see it being a
lubrication problem if the other tappets
are quiet, oil flow is likely okay.

I think the tappet would need to be
cleaned or replaced and cam checked
for flat spots. Some people have
had luck just by trying a different
grade of oil. Most use 10W40 cycle oil.
There is one type of pennzoil that
is supposed to help noisy tappets,
but I don't know if it has additives
that would be bad for clutch plates.

-you could take your serial number
and check with Honda for any recalls,
Some bikes in the 80's had oil passageway
problems, I can't remember if it was
honda or maybe suzuki.