Re: Cylinder head noises

[Glenn Merrell <gmerrel@domain.elided>]

Hello Graham and All,
    Without actually hearing the noise, it is not possible to determine
what the actual problem is.  From what you describe, the noise MAY BE a
sticking tappet.  What is happening is that the tappet may be binding in
its hole.  When the valve returns to its normal closed position, the
tappet actually rises off the top of the valve.  Next rotation of the
cam forces the tappet back onto the valve and pallet with a "whack".
Oversize tappets are available, but may require machining.
    Not to cause you undue worry, but the potential for damage is this:
When the tappet sticks in the "up" position, the pallet shim is retained
on the tappet underside by oil surface tension.  The positioning of the
pallet shim is the round top hole of the valve spring collar.  If the
valves are in need of adjustment and gaps are wider than specification,
there is the potential for the pallet shim to drift out of its position
when the tappet sticks in the "up" position.  The next down stroke
compresses the valve spring collar between the shifted pallet and
tappet, releasing the valve "keepers" or split cones, releasing the
valve into the cylinder.
    There is a technical bulletin that addresses a root cause of
dropping valves in the Dolomite and Dolomite Sprint engines (similar
head design as the Stag) caused by the use of an incorrect pallet shim.
The pallet is an Austin Morris type of pallet shim having a chamfered
edge as opposed to the Triumph/BL sharp edge pallet shim.
    It is a known problem that the tappet guide wall clearance widens
with the Stag heads through normal wear, and if regular routine
maintenance like oil and filter changes were neglected, this wear occurs
more rapidly. The tappets are steel, the tappet guides are only machined
in the aluminum cylinder head.   The wear causes the tappet buckets to
bind in the tappet guide hole.
    Like Tony Hart  repeatedly stresses, there is nothing wrong with the
design of the Stag V8 that regular routine maintenance will not correct,
this includes tappet guide wear and refitting larger tappets when
needed.   But also realize that a hot carbon deposit on that cylinder
could cause pre-ignition that will also rattle that valve pair
associated with the hot spot.  This is why you should consult a
specialist before too long, and get an opinion from someone who is
regurlarly into the Stag engine.

    There have been comments made about causing undue worry by placing
information on this digest.  My opinion is that it is better to do your
preventative maintenance and have a reliable running Stag, then wait for
the expensive repair job.  Graham, you are correct, if the Stag engine
is making a noise, it is telling you something. Sometime down the road,
it will break if you ignore it.

In My Humble Opinion....

Regards,
Glenn  Merrell

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