[Healeys] Valve clearances

[Bob Spidell]

I've set valve lash cold, then checked them warm and not seen an 
appreciable difference.

On another note, I'm a convert on the "set the gap per the cam builder's 
specs."  Next job for the BJ8: set valve lash to 0.015" per DWR spec.

Bob

On 1/13/2019 3:23 PM, Michael Salter wrote:
> This is another subject that I often wonder about.
> If the valve clearance is there to ensure that the valves are fully 
> closed when the engine is hot then why, when I check the clearances on 
> a hot engine after a dyno run, are they hardly any less than they were 
> cold?
> I can appreciate that the valve train components grow because of the 
> heat but surely the block and head and rocker shaft pedistals also 
> grow and thus there is little if any net change.
> I also appreciate that the exhaust valve stem get really hot but ????
> Just wondering....
>
> M
>
> On Sun, Jan 13, 2019, 6:42 AM WILLIAM B LAWRENCE <ynotink at msn.com 
> <mailto:ynotink at msn.com> wrote:
>
>     I disagree that valve clearances are not critical. As the engine
>     comes up to temperature the metal parts of the valve train
>     (valves, lifters, push rods, the head itself and the rocker shaft
>     towers) increase in length and the valve clearances are calculated
>     to assure that this expansion isn't allowed to affect the sealing
>     of the valves on their seats. If the valves are set too tight they
>     reach a point where they won't touch the seats and therefore won't
>     seal. Hot gases rushing through the gaps will quickly erode the
>     valves. Also increasing the duration and/or lift of the cam has
>     the effect of the  decreasing the length of the opening and
>     closing ramps on the back side of the cam This reduces the length
>     of time (dwell) the valve remains on the seat. Increasing the
>     valve clearance restores the dwell time the valve needs to
>     transfer its heat load to the cooling system through the valve
>     seat and the cylinder head. Too little dwell time or the lack of
>     proper valve sealing are two causes of burned valves.
>
>     In my own experience I installed an Isky cam with a grind a little
>     more aggressive than the 100M cam and set the clearances to 0.012"
>     per the manual. Within about 2,000 miles the exhaust valves were
>     trashed. I then took the time to read the Isky installation
>     instructions which specifically state the valve clearance needs to
>     be set to 0.018". I re-installed the head with new valves and set
>     them to Isky's spec and never had another problem with burned valves.
>
>     Follow the cam grinder's recommendations and you will avoid trouble.
>
>     Bill Lawrence
>     BN1 #554
>     ------------------------------------------------------------------------
>     *From:* Healeys <healeys-bounces at autox.team.net
>     <mailto:healeys-bounces at autox.team.net>> on behalf of Bob Spidell
>     <bspidell at comcast.net <mailto:bspidell at comcast.net>>
>     *Sent:* Saturday, January 12, 2019 11:10 PM
>     *To:* Michael MacLean; healeys at autox.team.net
>     <mailto:healeys at autox.team.net>
>     *Subject:* Re: [Healeys] Valve clearances
>
>     I should note the rockers are pretty noisy at 0.015; IIRC I
>     tightened them up just a bit.
>
>
>
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