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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."Â 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@msn.com
>
> 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@autox.team.net
> *Sent:* Saturday, January 12, 2019 11:10 PM
> *To:* Michael MacLean; healeys@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.
>
>
>
> Unsubscribe/Manage:
> http://autox.team.net/mailman/options/healeys/michaelsalter@gmail.com
>
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<p>I've set valve lash cold, then checked them warm and not seen an
appreciable difference.</p>
<p>On another note, I'm a convert on the "set the gap per the cam
builder's specs."Â Next job for the BJ8: set valve lash to 0.015"
per DWR spec.<br>
</p>
<p>Bob<br>
</p>
<div class="moz-cite-prefix">On 1/13/2019 3:23 PM, Michael Salter
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAB3i7L+hckqT__OLe1o1_4BjwSu8nDx1cYEoto9zspJCv_28Wg@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="auto">This is another subject that I often wonder
about.Â
<div dir="auto">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,Â
are they hardly any less than they were cold?</div>
<div dir="auto">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.</div>
<div dir="auto">I also appreciate that the exhaust valve stem
get really hot but ????</div>
<div dir="auto">Just wondering....</div>
<div dir="auto"><br>
</div>
<div dir="auto">M</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr">On Sun, Jan 13, 2019, 6:42 AM WILLIAM B LAWRENCE
<<a href="mailto:ynotink@msn.com";
moz-do-not-send="true">ynotink@msn.com</a>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">
<div
style="font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">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 i<span
style="font-family:Calibri,Helvetica,sans-serif;background-color:rgb(255,255,255);display:inline!important">ncreasing
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.</span></div>
<div
style="font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)"><br>
</div>
<div
style="font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">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.</div>
<div
style="font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)"><br>
</div>
<div
style="font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">Follow
the cam grinder's recommendations and you will avoid
trouble.</div>
<div
style="font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)"><br>
</div>
<div
style="font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">Bill
Lawrence</div>
<div
style="font-family:Calibri,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">BN1
#554</div>
<hr style="display:inline-block;width:98%">
<div id="m_1603937236670712738divRplyFwdMsg" dir="ltr"><font
style="font-size:11pt" face="Calibri, sans-serif"
color="#000000"><b>From:</b> Healeys <<a
href="mailto:healeys-bounces@autox.team.net";
target="_blank" rel="noreferrer"
moz-do-not-send="true">healeys-bounces@autox.team.net</a>>
on behalf of Bob Spidell <<a
href="mailto:bspidell@comcast.net"; target="_blank"
rel="noreferrer"
moz-do-not-send="true">bspidell@comcast.net</a>><br>
<b>Sent:</b> Saturday, January 12, 2019 11:10 PM<br>
<b>To:</b> Michael MacLean; <a
href="mailto:healeys@autox.team.net"; target="_blank"
rel="noreferrer"
moz-do-not-send="true">healeys@autox.team.net</a><br>
<b>Subject:</b> Re: [Healeys] Valve clearances</font>
<div>Â </div>
</div>
<div style="background-color:#ffffff">
<p>I should note the rockers are pretty noisy at 0.015;
IIRC I tightened them up just a bit.<br>
</p>
<br>
</div>
</div>
<br>
Unsubscribe/Manage: <a
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