<div dir="ltr"><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">Hi Raymond,<br></div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">I have often noticed more wear on exhaust valve guides than inlets and I think that is to be expected.<br></div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">As the engine runs oil mist from within the rocker cover deposits oil on the valve stems above the guide .<br>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. <br></div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">In the case of the exhaust guide the 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 exhaust gasses is from the port up through the clearance space and into the rocker 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 stem and guide.<br></div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">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.<br><br></div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">Michael S<br></div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small">BN1 #174<br></div><div class="gmail_default" style="font-family:comic sans ms,sans-serif;font-size:small"><br><br><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Sun, Mar 29, 2015 at 3:27 AM, Austin Healey <span dir="ltr"><<a href="mailto:pajtamuvek@gmail.com" target="_blank">pajtamuvek@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">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.<div><br></div><div>g</div></div><div class="gmail_extra"><br><div class="gmail_quote"><span class="">2015-03-29 8:57 GMT+02:00 RAYMOND SMITHSON <span dir="ltr"><<a href="mailto:rjsmithson@shaw.ca" target="_blank">rjsmithson@shaw.ca</a>></span>:<br></span><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span class=""><div><div style="font-family:arial,helvetica,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. Is this a common occurrence?</div></div></div><br></span>_______________________________________________<br>
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