Re: Cylinder head noises

["K.G. Nicholson" <kgn@domain.elided>]

Thank you for your comments regarding possible causes for the tapping in my
cylinder head. Your explanation sounds very plausible to me.  This is a little
alarming since the heads were rebuilt by Stag specialists 9000 miles ago and
the oil and filter have been changed every 3000 miles.  I suppose one tappet
bore may be little worn and this is causing the "sticking" for a couple of
minutes while the engine is cold. I will remove the camshaft and look for some
suspect bores but suspect that the head will have to come off for a proper
inspection.  

Regards 

Graham Nicholson
For Tony Gee and Partners

On Thu, 8 Oct 1998, Glenn Merrell wrote:

> 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
> 
> "Keep Your Stag Cool, Install a NEW Composite Cowl Today"
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> Triumph Stag Register USA VP
> membership inquiry's to:
> Mike Wattam <101714.1343@domain.elided>
> 
> 
> 
> 
>