[Healeys] Valve guides

[Michael Salter]

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 at 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 at 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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-- 
*If you can't fix it with a hammer, you've got an electrical problem.*
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