CB750 DOHC: Ticking sound

 This is about a 1980 CB750 (DOHC).
http://mysite.verizon.net/barrettmanor/EngineTick.mp3
is a link to an mp3 I just recorded of the worrisome ticking sound it's
making.

It doesn't do it until it warms up a bit.

I've done the cam-chain auto-adjustments, although the upper chain is near
its limit.
To me this doesn't sound like what I'd expect from a loose chain though,
which I would think would be more of a continuous grating as each link
rubbed, rather than a tick per revolution.
It coming more from the #1 side, near the top, but it's hard to pin down
more than that.  If I had to guess I'd say around the #1 or #2 intake
valves.  (I even tried the old trick of listening through a tube placed at
various spots but that was no use at all.)

I've checked/set the valve clearances multiple times, and they're all
between .004 and .006" (.102 - .152mm).
I don't see any broken links in the chains, or any obvious wear marks.

Is there a minimum recommended shim thickness?  On the exhaust side I'm down
to a 260 on one valve.

With the engine out, I've turned it over by hand countless times, and
haven't spotted anything.  There's no vertical play in the piston rods.

Any suggestions on what to check next would be appreciated.
 

 

"Ticking" noises can often be traced to exhaust leakage.

However, it's usually the warm up that results in a dec-
rease, rather than the onset. But, I'd cross that off the
suspect list by having a good look there.

 

<Nods>


--
BMW K1100LT  Ducati 750SS  Honda CB400F & SH50  Triumph Street Triple
GHPOTHUF#1 chateaudotmurrayatidnetdotcom
Nothing is more dangerous than an ignoramus with a workshop manual,
a 'can-do' attitude and a cheap set of tools

 wrote:


Sounds a lot like an exhaust leak near the cylinder head. Probably a
broken exhaust gasket or a crack in the exhaust pipe.
--
RoRo

 I put in new exhaust gaskets when I put it back together a week ago, and
re-torqued the exhaust manifolds just before I made that recording.  I'll
check again though.