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--089e013d1e0e83b7a0051271126a
Hi Raymond,
I have often noticed more wear on exhaust valve guides than inlets and I
think that is to be expected.
As the engine runs oil mist from within the rocker cover deposits oil on
the valve stems above the guide .
As you know Healey engines do not have "umbrella" style valve seals so, in
the case of the inlet valve, there is a natural flow of air, in minute
quantities, down that gap because the air pressure in the intake port is
typically considerably lower than that in the rocker cover. This flow of
air draws oil down into the clearance space between the guide and the stem
and so provides excellent lubrication.
In the case of the exhaust guide the opposite is the case.
There is typically a slightly higher pressure in the exhaust port, called
exhaust back pressure, so the flow of hot exhaust gasses is from the port
up through the clearance space and into the rocker cover.
As a consequence of this flow direction little or no oil from the rocker
cover makes its way down the exhaust guide to lubricate the stem and guide.
Fortunately, as any machinist will tell you, cast iron contains a lot of
free carbon flakes so is to some degree self lubricating. As a result of
this carbon wear is kept to a minimum and usually only becomes apparent in
very high mileage engines.
Michael S
BN1 #174
On Sun, Mar 29, 2015 at 3:27 AM, Austin Healey <pajtamuvek@gmail.com> wrote:
> Exhaust guides usually wear out faster. They might have been replaced at a
> point, while inlets were considered ok at that time. Just an idea.
>
> g
>
> 2015-03-29 8:57 GMT+02:00 RAYMOND SMITHSON <rjsmithson@shaw.ca>:
>
>> Wow,
>> Here I thought it was a simple question. I'm aware of the difference
>> between bronze and cast iron guides. What I was interested in was was the
>> substantial difference in wear between the intake and exhaust guides, both
>> of which are cast iron. Is this a common occurrence?
>>
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>>
>
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--
*If you can't fix it with a hammer, you've got an electrical problem.*
--089e013d1e0e83b7a0051271126a
Content-Transfer-Encoding: quoted-printable
<div dir=3D"ltr"><div class=3D"gmail_default" style=3D"font-family:comic sa=
ns ms,sans-serif;font-size:small">Hi Raymond,<br></div><div class=3D"gmail_=
default" style=3D"font-family:comic sans ms,sans-serif;font-size:small">I h=
ave often noticed more wear on exhaust valve guides than inlets and I think=
that is to be expected.<br></div><div class=3D"gmail_default" style=3D"fon=
t-family:comic sans ms,sans-serif;font-size:small">As the engine runs oil m=
ist from within the rocker cover deposits oil on the valve stems above the =
guide .<br>As you know Healey engines do not have "umbrella" styl=
e valve seals so, in the case of the inlet valve, there is a natural flow o=
f air, in minute quantities, down that gap=20
because the air pressure in the intake port is typically considerably=20
lower than that in the rocker cover. This flow of air draws oil down into t=
he clearance space between the guide and the stem and so provides excellent=
lubrication. <br></div><div class=3D"gmail_default" style=3D"font-family:c=
omic sans ms,sans-serif;font-size:small">In the case of the exhaust guide t=
he opposite is the case. <br>There is typically a slightly higher pressure =
in the exhaust port, called exhaust back pressure, so the flow of hot exhau=
st gasses is from the port up through the clearance space and into the rock=
er cover. <br>As a consequence of this flow direction little or no oil from=
the rocker cover makes its way down the exhaust guide to lubricate the ste=
m and guide.<br></div><div class=3D"gmail_default" style=3D"font-family:com=
ic sans ms,sans-serif;font-size:small">Fortunately, as any machinist will t=
ell you, cast iron contains a lot of free carbon flakes so is to some degre=
e self lubricating. As a result of this carbon wear is kept to a minimum an=
d usually only becomes apparent in very high mileage engines.<br><br></div>=
<div class=3D"gmail_default" style=3D"font-family:comic sans ms,sans-serif;=
font-size:small">Michael S<br></div><div class=3D"gmail_default" style=3D"f=
ont-family:comic sans ms,sans-serif;font-size:small">BN1 #174<br></div><div=
class=3D"gmail_default" style=3D"font-family:comic sans ms,sans-serif;font=
-size:small"><br><br><br></div></div><div class=3D"gmail_extra"><br><div cl=
ass=3D"gmail_quote">On Sun, Mar 29, 2015 at 3:27 AM, Austin Healey <span di=
r=3D"ltr"><<a href=3D"mailto:pajtamuvek@gmail.com"; target=3D"_blank">paj=
tamuvek@gmail.com</a>></span> wrote:<br><blockquote class=3D"gmail_quote=
" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><=
div dir=3D"ltr">Exhaust guides usually wear out faster. They might have bee=
n replaced at a point, while inlets were considered ok at that time. Just a=
n idea.<div><br></div><div>g</div></div><div class=3D"gmail_extra"><br><div=
class=3D"gmail_quote"><span class=3D"">2015-03-29 8:57 GMT+02:00 RAYMOND S=
MITHSON <span dir=3D"ltr"><<a href=3D"mailto:rjsmithson@shaw.ca"; target=
=3D"_blank">rjsmithson@shaw.ca</a>></span>:<br></span><blockquote class=
=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padd=
ing-left:1ex"><span class=3D""><div><div style=3D"font-family:arial,helveti=
ca,sans-serif;font-size:10pt;color:#000000">Wow,<div>Here I thought it was =
a simple question. I'm aware of the difference between bronze and cast =
iron guides. What I was interested in was was the substantial difference in=
wear between the intake and exhaust guides, both of which are cast iron. I=
s this a common occurrence?</div></div></div><br></span>___________________=
____________________________<br>
nk">http://www.team.net/donate.html</a><br>
Archive: <a href=3D"http://www.team.net/archive"; target=3D"_blank">http://w=
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.team.net/forums</a><br>
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ions/healeys/pajtamuvek@gmail.com</a><br>
<br>
<br></blockquote></div><br></div>
<br>_______________________________________________<br>
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<br></blockquote></div><br><br clear=3D"all"><br>-- <br><div class=3D"gmail=
_signature"><div dir=3D"ltr"><div><div dir=3D"ltr"><i><font><span style=3D"=
color:black">If you can't fix it with a hammer, you've got an elect=
rical problem.</span></font></i><br><br><div></div><div></div><div></div></=
div></div></div></div>
</div>
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